版本記錄

前言

OpenGL ES圖形庫項目中一直也沒用過，最近也想學(xué)著使用這個圖形庫，感覺還是很有意思，也就自然想著好好的總結(jié)一下焰络，希望對大家能有所幫助。
1. OpenGL 圖形庫使用（一） —— 概念基礎(chǔ)
2. OpenGL 圖形庫使用（二） —— 渲染模式符喝、對象闪彼、擴(kuò)展和狀態(tài)機(jī)
3. OpenGL 圖形庫使用（三） —— 著色器、數(shù)據(jù)類型與輸入輸出
4. OpenGL 圖形庫使用（四） —— Uniform及更多屬性
5. OpenGL 圖形庫使用（五） —— 紋理
6. OpenGL 圖形庫使用（六） —— 變換
7. OpenGL 圖形庫的使用（七）—— 坐標(biāo)系統(tǒng)之五種不同的坐標(biāo)系統(tǒng)（一）
8. OpenGL 圖形庫的使用（八）—— 坐標(biāo)系統(tǒng)之3D效果（二）
9. OpenGL 圖形庫的使用（九）—— 攝像機(jī)（一）
10. OpenGL 圖形庫的使用（十）—— 攝像機(jī)（二）
11. OpenGL 圖形庫的使用（十一）—— 光照之顏色
12. OpenGL 圖形庫的使用（十二）—— 光照之基礎(chǔ)光照
13. OpenGL 圖形庫的使用（十三）—— 光照之材質(zhì)
14. OpenGL 圖形庫的使用（十四）—— 光照之光照貼圖

投光物

我們目前使用的光照都來自于空間中的一個點(diǎn)协饲。它能給我們不錯的效果畏腕，但現(xiàn)實(shí)世界中，我們有很多種類的光照囱稽，每種的表現(xiàn)都不同郊尝。將光投射(Cast)到物體的光源叫做投光物(Light Caster)。在這一節(jié)中战惊，我們將會討論幾種不同類型的投光物流昏。學(xué)會模擬不同種類的光源是又一個能夠進(jìn)一步豐富場景的工具。

我們首先將會討論定向光(Directional Light)吞获，接下來是點(diǎn)光源(Point Light)况凉，它是我們之前學(xué)習(xí)的光源的拓展，最后我們將會討論聚光(Spotlight)各拷。在下一節(jié)中我們將討論如何將這些不同種類的光照類型整合到一個場景之中刁绒。

平行光

當(dāng)一個光源處于很遠(yuǎn)的地方時，來自光源的每條光線就會近似于互相平行烤黍。不論物體和/或者觀察者的位置知市，看起來好像所有的光都來自于同一個方向。當(dāng)我們使用一個假設(shè)光源處于無限遠(yuǎn)處的模型時速蕊，它就被稱為定向光嫂丙，因為它的所有光線都有著相同的方向，它與光源的位置是沒有關(guān)系的规哲。

定向光非常好的一個例子就是太陽跟啤。太陽距離我們并不是無限遠(yuǎn)，但它已經(jīng)遠(yuǎn)到在光照計算中可以把它視為無限遠(yuǎn)了唉锌。所以來自太陽的所有光線將被模擬為平行光線隅肥，我們可以在下圖看到：

因為所有的光線都是平行的，所以物體與光源的相對位置是不重要的袄简，因為對場景中每一個物體光的方向都是一致的腥放。由于光的位置向量保持一致，場景中每個物體的光照計算將會是類似的痘番。

我們可以定義一個光線方向向量而不是位置向量來模擬一個定向光捉片。著色器的計算基本保持不變平痰，但這次我們將直接使用光的direction向量而不是通過direction來計算lightDir向量粤策。

struct Light {
    // vec3 position; // 使用定向光就不再需要了
    vec3 direction;

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};
...
void main()
{
  vec3 lightDir = normalize(-light.direction);
  ...
}

注意我們首先對light.direction向量取反矮冬。我們目前使用的光照計算需求一個從片段至光源的光線方向，但人們更習(xí)慣定義定向光為一個從光源出發(fā)的全局方向别伏。所以我們需要對全局光照方向向量取反來改變它的方向莹规，它現(xiàn)在是一個指向光源的方向向量了赔蒲。而且，記得對向量進(jìn)行標(biāo)準(zhǔn)化良漱，假設(shè)輸入向量為一個單位向量是很不明智的舞虱。

最終的lightDir向量將和以前一樣用在漫反射和鏡面光計算中。

為了清楚地展示定向光對多個物體具有相同的影響母市，我們將會再次使用坐標(biāo)系統(tǒng)章節(jié)最后的那個箱子派對的場景矾兜。如果你錯過了派對，我們先定義了十個不同的箱子位置患久，并對每個箱子都生成了一個不同的模型矩陣椅寺，每個模型矩陣都包含了對應(yīng)的局部-世界坐標(biāo)變換：

for(unsigned int i = 0; i < 10; i++)
{
    glm::mat4 model;
    model = glm::translate(model, cubePositions[i]);
    float angle = 20.0f * i;
    model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
    lightingShader.setMat4("model", model);

    glDrawArrays(GL_TRIANGLES, 0, 36);
}

同時，不要忘記定義光源的方向（注意我們將方向定義為從光源出發(fā)的方向蒋失，你可以很容易看到光的方向朝下）返帕。

lightingShader.setVec3("light.direction", -0.2f, -1.0f, -0.3f);

我們一直將光的位置和位置向量定義為vec3，但一些人會喜歡將所有的向量都定義為vec4篙挽。當(dāng)我們將位置向量定義為一個vec4時荆萤，很重要的一點(diǎn)是要將w分量設(shè)置為1.0，這樣變換和投影才能正確應(yīng)用铣卡。然而链韭，當(dāng)我們定義一個方向向量為vec4的時候，我們不想讓位移有任何的效果（因為它僅僅代表的是方向）煮落，所以我們將w分量設(shè)置為0.0梧油。

方向向量就會像這樣來表示：vec4(0.2f, 1.0f, 0.3f, 0.0f)。這也可以作為一個快速檢測光照類型的工具：你可以檢測w分量是否等于1.0州邢，來檢測它是否是光的位置向量；w分量等于0.0褪子，則它是光的方向向量量淌，這樣就能根據(jù)這個來調(diào)整光照計算了：

if(lightVector.w == 0.0) // 注意浮點(diǎn)數(shù)據(jù)類型的誤差
  // 執(zhí)行定向光照計算
else if(lightVector.w == 1.0)
  // 根據(jù)光源的位置做光照計算（與上一節(jié)一樣）

你知道嗎：這正是舊OpenGL（固定函數(shù)式）決定光源是定向光還是位置光源(Positional Light Source)的方法，并根據(jù)它來調(diào)整光照嫌褪。

如果你現(xiàn)在編譯程序呀枢，在場景中自由移動，你就可以看到好像有一個太陽一樣的光源對所有的物體投光笼痛。你能注意到漫反射和鏡面光分量的反應(yīng)都好像在天空中有一個光源的感覺嗎裙秋？它會看起來像這樣：

你可以在這里找到程序的所有代碼琅拌。

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb_image.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    // build and compile shaders
    // -------------------------
    Shader lightingShader("5.1.light_casters.vs", "5.1.light_casters.fs");
    Shader lampShader("5.1.lamp.vs", "5.1.lamp.fs");

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        // positions          // normals           // texture coords
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f
    };
    // positions all containers
    glm::vec3 cubePositions[] = {
        glm::vec3( 0.0f,  0.0f,  0.0f),
        glm::vec3( 2.0f,  5.0f, -15.0f),
        glm::vec3(-1.5f, -2.2f, -2.5f),
        glm::vec3(-3.8f, -2.0f, -12.3f),
        glm::vec3( 2.4f, -0.4f, -3.5f),
        glm::vec3(-1.7f,  3.0f, -7.5f),
        glm::vec3( 1.3f, -2.0f, -2.5f),
        glm::vec3( 1.5f,  2.0f, -2.5f),
        glm::vec3( 1.5f,  0.2f, -1.5f),
        glm::vec3(-1.3f,  1.0f, -1.5f)
    };
    // first, configure the cube's VAO (and VBO)
    unsigned int VBO, cubeVAO;
    glGenVertexArrays(1, &cubeVAO);
    glGenBuffers(1, &VBO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindVertexArray(cubeVAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    // second, configure the light's VAO (VBO stays the same; the vertices are the same for the light object which is also a 3D cube)
    unsigned int lightVAO;
    glGenVertexArrays(1, &lightVAO);
    glBindVertexArray(lightVAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    // note that we update the lamp's position attribute's stride to reflect the updated buffer data
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // load textures (we now use a utility function to keep the code more organized)
    // -----------------------------------------------------------------------------
    unsigned int diffuseMap = loadTexture(FileSystem::getPath("resources/textures/container2.png").c_str());
    unsigned int specularMap = loadTexture(FileSystem::getPath("resources/textures/container2_specular.png").c_str());

    // shader configuration
    // --------------------
    lightingShader.use();
    lightingShader.setInt("material.diffuse", 0);
    lightingShader.setInt("material.specular", 1);


    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // be sure to activate shader when setting uniforms/drawing objects
        lightingShader.use();
        lightingShader.setVec3("light.direction", -0.2f, -1.0f, -0.3f);
        lightingShader.setVec3("viewPos", camera.Position);

        // light properties
        lightingShader.setVec3("light.ambient", 0.2f, 0.2f, 0.2f);
        lightingShader.setVec3("light.diffuse", 0.5f, 0.5f, 0.5f);
        lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);

        // material properties
        lightingShader.setFloat("material.shininess", 32.0f);

        // view/projection transformations
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        lightingShader.setMat4("projection", projection);
        lightingShader.setMat4("view", view);

        // world transformation
        glm::mat4 model;
        lightingShader.setMat4("model", model);

        // bind diffuse map
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, diffuseMap);
        // bind specular map
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, specularMap);

        // render the cube
        // glBindVertexArray(cubeVAO);
        // glDrawArrays(GL_TRIANGLES, 0, 36);*/

        // render containers
        glBindVertexArray(cubeVAO);
        for (unsigned int i = 0; i < 10; i++)
        {
            // calculate the model matrix for each object and pass it to shader before drawing
            glm::mat4 model;
            model = glm::translate(model, cubePositions[i]);
            float angle = 20.0f * i;
            model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
            lightingShader.setMat4("model", model);

            glDrawArrays(GL_TRIANGLES, 0, 36);
        }


        // a lamp object is weird when we only have a directional light, don't render the light object
        // lampShader.use();
        // lampShader.setMat4("projection", projection);
        // lampShader.setMat4("view", view);
        // model = glm::mat4();
        // model = glm::translate(model, lightPos);
        // model = glm::scale(model, glm::vec3(0.2f)); // a smaller cube
        // lampShader.setMat4("model", model);

        // glBindVertexArray(lightVAO);
        // glDrawArrays(GL_TRIANGLES, 0, 36);


        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteVertexArrays(1, &lightVAO);
    glDeleteBuffers(1, &VBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}


// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}

點(diǎn)光源

定向光對于照亮整個場景的全局光源是非常棒的，但除了定向光之外我們也需要一些分散在場景中的點(diǎn)光源(Point Light)摘刑。點(diǎn)光源是處于世界中某一個位置的光源进宝，它會朝著所有方向發(fā)光，但光線會隨著距離逐漸衰減枷恕。想象作為投光物的燈泡和火把党晋，它們都是點(diǎn)光源。

在之前的教程中徐块，我們一直都在使用一個（簡化的）點(diǎn)光源未玻。我們在給定位置有一個光源，它會從它的光源位置開始朝著所有方向散射光線胡控。然而扳剿，我們定義的光源模擬的是永遠(yuǎn)不會衰減的光線，這看起來像是光源亮度非常的強(qiáng)昼激。在大部分的3D模擬中庇绽，我們都希望模擬的光源僅照亮光源附近的區(qū)域而不是整個場景。

如果你將10個箱子加入到上一節(jié)光照場景中癣猾，你會注意到在最后面的箱子和在燈面前的箱子都以相同的強(qiáng)度被照亮敛劝，并沒有定義一個公式來將光隨距離衰減。我們希望在后排的箱子與前排的箱子相比僅僅是被輕微地照亮纷宇。

衰減

隨著光線傳播距離的增長逐漸削減光的強(qiáng)度通常叫做衰減(Attenuation)夸盟。隨距離減少光強(qiáng)度的一種方式是使用一個線性方程。這樣的方程能夠隨著距離的增長線性地減少光的強(qiáng)度像捶，從而讓遠(yuǎn)處的物體更暗上陕。然而，這樣的線性方程通常會看起來比較假拓春。在現(xiàn)實(shí)世界中释簿，燈在近處通常會非常亮，但隨著距離的增加光源的亮度一開始會下降非撑鹈В快庶溶，但在遠(yuǎn)處時剩余的光強(qiáng)度就會下降的非常緩慢了。所以懂鸵，我們需要一個不同的公式來減少光的強(qiáng)度偏螺。

在這里d代表了片段距光源的距離。接下來為了計算衰減值匆光，我們定義3個（可配置的）項：常數(shù)項Kc套像、一次項Kl和二次項Kq。

• 常數(shù)項通常保持為1.0终息，它的主要作用是保證分母永遠(yuǎn)不會比1小夺巩，否則的話在某些距離上它反而會增加強(qiáng)度贞让，這肯定不是我們想要的效果。
• 一次項會與距離值相乘柳譬，以線性的方式減少強(qiáng)度喳张。
• 二次項會與距離的平方相乘，讓光源以二次遞減的方式減少強(qiáng)度征绎。二次項在距離比較小的時候影響會比一次項小很多蹲姐，但當(dāng)距離值比較大的時候它就會比一次項更大了。

由于二次項的存在人柿，光線會在大部分時候以線性的方式衰退柴墩，直到距離變得足夠大，讓二次項超過一次項凫岖，光的強(qiáng)度會以更快的速度下降江咳。這樣的結(jié)果就是，光在近距離時亮度很高哥放，但隨著距離變遠(yuǎn)亮度迅速降低歼指，最后會以更慢的速度減少亮度。下面這張圖顯示了在100的距離內(nèi)衰減的效果：

你可以看到光在近距離的時候有著最高的強(qiáng)度甥雕，但隨著距離增長踩身，它的強(qiáng)度明顯減弱，并緩慢地在距離大約100的時候強(qiáng)度接近0社露。這正是我們想要的挟阻。

1. 選擇正確的值

但是，該對這三個項設(shè)置什么值呢峭弟？正確地設(shè)定它們的值取決于很多因素：環(huán)境附鸽、希望光覆蓋的距離、光的類型等瞒瘸。在大多數(shù)情況下坷备，這都是經(jīng)驗的問題，以及適量的調(diào)整情臭。下面這個表格顯示了模擬一個（大概）真實(shí)的省撑，覆蓋特定半徑（距離）的光源時，這些項可能取的一些值俯在。第一列指定的是在給定的三項時光所能覆蓋的距離丁侄。這些值是大多數(shù)光源很好的起始點(diǎn)，它們由Ogre3D的Wiki所提供：

你可以看到朝巫，常數(shù)項Kc在所有的情況下都是1.0。一次項Kl為了覆蓋更遠(yuǎn)的距離通常都很小石景，二次項Kq甚至更小劈猿。嘗試對這些值進(jìn)行實(shí)驗拙吉，看看它們在你的實(shí)現(xiàn)中有什么效果。在我們的環(huán)境中揪荣，32到100的距離對大多數(shù)的光源都足夠了筷黔。

2. 實(shí)現(xiàn)衰減

為了實(shí)現(xiàn)衰減，在片段著色器中我們還需要三個額外的值：也就是公式中的常數(shù)項仗颈、一次項和二次項佛舱。它們最好儲存在之前定義的Light結(jié)構(gòu)體中。注意我們使用上一節(jié)中計算lightDir的方法挨决，而不是上面定向光部分的请祖。

struct Light {
    vec3 position;  

    vec3 ambient;
    vec3 diffuse;
    vec3 specular;

    float constant;
    float linear;
    float quadratic;
};

然后我們將在OpenGL中設(shè)置這些項：我們希望光源能夠覆蓋50的距離，所以我們會使用表格中對應(yīng)的常數(shù)項脖祈、一次項和二次項：

lightingShader.setFloat("light.constant",  1.0f);
lightingShader.setFloat("light.linear",    0.09f);
lightingShader.setFloat("light.quadratic", 0.032f);

在片段著色器中實(shí)現(xiàn)衰減還是比較直接的：我們根據(jù)公式計算衰減值肆捕，之后再分別乘以環(huán)境光、漫反射和鏡面光分量盖高。

我們?nèi)孕枰街芯喙庠吹木嚯x慎陵，還記得我們是怎么計算一個向量的長度的嗎？我們可以通過獲取片段和光源之間的向量差喻奥，并獲取結(jié)果向量的長度作為距離項席纽。我們可以使用GLSL內(nèi)建的length函數(shù)來完成這一點(diǎn)：

float distance    = length(light.position - FragPos);
float attenuation = 1.0 / (light.constant + light.linear * distance + 
                light.quadratic * (distance * distance));

接下來，我們將包含這個衰減值到光照計算中撞蚕，將它分別乘以環(huán)境光润梯、漫反射和鏡面光顏色。

我們可以將環(huán)境光分量保持不變诈豌，讓環(huán)境光照不會隨著距離減少仆救，但是如果我們使用多于一個的光源，所有的環(huán)境光分量將會開始疊加矫渔，所以在這種情況下我們也希望衰減環(huán)境光照彤蔽。簡單實(shí)驗一下，看看什么才能在你的環(huán)境中效果最好庙洼。

ambient  *= attenuation; 
diffuse  *= attenuation;
specular *= attenuation;

如果你運(yùn)行程序的話顿痪，你會獲得這樣的結(jié)果：

你可以看到，只有前排的箱子被照亮的油够，距離最近的箱子是最亮的蚁袭。后排的箱子一點(diǎn)都沒有照亮，因為它們離光源實(shí)在是太遠(yuǎn)了石咬。你可以在這里找到程序的代碼揩悄。

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb_image.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

// lighting
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
        glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    // build and compile our shader zprogram
    // ------------------------------------
    Shader lightingShader("5.2.light_casters.vs", "5.2.light_casters.fs");
    Shader lampShader("5.2.lamp.vs", "5.2.lamp.fs");

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        // positions          // normals           // texture coords
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f
    };
    // positions all containers
    glm::vec3 cubePositions[] = {
        glm::vec3( 0.0f,  0.0f,  0.0f),
        glm::vec3( 2.0f,  5.0f, -15.0f),
        glm::vec3(-1.5f, -2.2f, -2.5f),
        glm::vec3(-3.8f, -2.0f, -12.3f),
        glm::vec3( 2.4f, -0.4f, -3.5f),
        glm::vec3(-1.7f,  3.0f, -7.5f),
        glm::vec3( 1.3f, -2.0f, -2.5f),
        glm::vec3( 1.5f,  2.0f, -2.5f),
        glm::vec3( 1.5f,  0.2f, -1.5f),
        glm::vec3(-1.3f,  1.0f, -1.5f)
    };
    // first, configure the cube's VAO (and VBO)
    unsigned int VBO, cubeVAO;
    glGenVertexArrays(1, &cubeVAO);
    glGenBuffers(1, &VBO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindVertexArray(cubeVAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    // second, configure the light's VAO (VBO stays the same; the vertices are the same for the light object which is also a 3D cube)
    unsigned int lightVAO;
    glGenVertexArrays(1, &lightVAO);
    glBindVertexArray(lightVAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    // note that we update the lamp's position attribute's stride to reflect the updated buffer data
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // load textures (we now use a utility function to keep the code more organized)
    // -----------------------------------------------------------------------------
    unsigned int diffuseMap = loadTexture(FileSystem::getPath("resources/textures/container2.png").c_str());
    unsigned int specularMap = loadTexture(FileSystem::getPath("resources/textures/container2_specular.png").c_str());

    // shader configuration
    // --------------------
    lightingShader.use();
    lightingShader.setInt("material.diffuse", 0);
    lightingShader.setInt("material.specular", 1);


    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // be sure to activate shader when setting uniforms/drawing objects
        lightingShader.use();
        lightingShader.setVec3("light.position", lightPos);
        lightingShader.setVec3("viewPos", camera.Position);

        // light properties
        lightingShader.setVec3("light.ambient", 0.2f, 0.2f, 0.2f);
        lightingShader.setVec3("light.diffuse", 0.5f, 0.5f, 0.5f);
        lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);
        lightingShader.setFloat("light.constant", 1.0f);
        lightingShader.setFloat("light.linear", 0.09f);
        lightingShader.setFloat("light.quadratic", 0.032f);

        // material properties
        lightingShader.setFloat("material.shininess", 32.0f);

        // view/projection transformations
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        lightingShader.setMat4("projection", projection);
        lightingShader.setMat4("view", view);

        // world transformation
        glm::mat4 model;
        lightingShader.setMat4("model", model);

        // bind diffuse map
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, diffuseMap);
        // bind specular map
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, specularMap);

        // render containers
        glBindVertexArray(cubeVAO);
        for (unsigned int i = 0; i < 10; i++)
        {
            // calculate the model matrix for each object and pass it to shader before drawing
            glm::mat4 model;
            model = glm::translate(model, cubePositions[i]);
            float angle = 20.0f * i;
            model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
            lightingShader.setMat4("model", model);

            glDrawArrays(GL_TRIANGLES, 0, 36);
        }


         // also draw the lamp object
         lampShader.use();
         lampShader.setMat4("projection", projection);
         lampShader.setMat4("view", view);
         model = glm::mat4();
         model = glm::translate(model, lightPos);
         model = glm::scale(model, glm::vec3(0.2f)); // a smaller cube
         lampShader.setMat4("model", model);

         glBindVertexArray(lightVAO);
         glDrawArrays(GL_TRIANGLES, 0, 36);


        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteVertexArrays(1, &lightVAO);
    glDeleteBuffers(1, &VBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}

點(diǎn)光源就是一個能夠配置位置和衰減的光源。它是我們光照工具箱中的又一個光照類型鬼悠。

聚光

我們要討論的最后一種類型的光是聚光(Spotlight)删性。聚光是位于環(huán)境中某個位置的光源亏娜，它只朝一個特定方向而不是所有方向照射光線。這樣的結(jié)果就是只有在聚光方向的特定半徑內(nèi)的物體才會被照亮蹬挺，其它的物體都會保持黑暗维贺。聚光很好的例子就是路燈或手電筒。

OpenGL中聚光是用一個世界空間位置巴帮、一個方向和一個切光角(Cutoff Angle)來表示的溯泣，切光角指定了聚光的半徑（譯注：是圓錐的半徑不是距光源距離那個半徑）。對于每個片段榕茧，我們會計算片段是否位于聚光的切光方向之間（也就是在錐形內(nèi)）垃沦，如果是的話，我們就會相應(yīng)地照亮片段雪猪。下面這張圖會讓你明白聚光是如何工作的：

• LightDir：從片段指向光源的向量栏尚。
• SpotDir：聚光所指向的方向。
• Phi?：指定了聚光半徑的切光角只恨。落在這個角度之外的物體都不會被這個聚光所照亮译仗。
• Thetaθ：LightDir向量和SpotDir向量之間的夾角。在聚光內(nèi)部的話θθ值應(yīng)該比?值小官觅。

所以我們要做的就是計算LightDir向量和SpotDir向量之間的點(diǎn)積（還記得它會返回兩個單位向量夾角的余弦值嗎纵菌？），并將它與切光角?值對比休涤。你現(xiàn)在應(yīng)該了解聚光究竟是什么了咱圆，下面我們將以手電筒的形式創(chuàng)建一個聚光。

手電筒

手電筒(Flashlight)是一個位于觀察者位置的聚光功氨，通常它都會瞄準(zhǔn)玩家視角的正前方序苏。基本上說捷凄，手電筒就是普通的聚光忱详，但它的位置和方向會隨著玩家的位置和朝向不斷更新。

所以跺涤，在片段著色器中我們需要的值有聚光的位置向量（來計算光的方向向量）匈睁、聚光的方向向量和一個切光角。我們可以將它們儲存在Light結(jié)構(gòu)體中：

struct Light {
    vec3  position;
    vec3  direction;
    float cutOff;
    ...
};

接下來我們將合適的值傳到著色器中：

lightingShader.setVec3("light.position",  camera.Position);
lightingShader.setVec3("light.direction", camera.Front);
lightingShader.setFloat("light.cutOff",   glm::cos(glm::radians(12.5f)));

你可以看到桶错，我們并沒有給切光角設(shè)置一個角度值航唆，反而是用角度值計算了一個余弦值，將余弦結(jié)果傳遞到片段著色器中院刁。這樣做的原因是在片段著色器中糯钙，我們會計算LightDir和SpotDir向量的點(diǎn)積，這個點(diǎn)積返回的將是一個余弦值而不是角度值，所以我們不能直接使用角度值和余弦值進(jìn)行比較超营。為了獲取角度值我們需要計算點(diǎn)積結(jié)果的反余弦鸳玩，這是一個開銷很大的計算。所以為了節(jié)約一點(diǎn)性能開銷演闭，我們將會計算切光角對應(yīng)的余弦值，并將它的結(jié)果傳入片段著色器中颓帝。由于這兩個角度現(xiàn)在都由余弦角來表示了，我們可以直接對它們進(jìn)行比較而不用進(jìn)行任何開銷高昂的計算吕座。

接下來就是計算θθ值瘪板，并將它和切光角?對比侮攀，來決定是否在聚光的內(nèi)部：

float theta = dot(lightDir, normalize(-light.direction));

if(theta > light.cutOff) 
{       
  // 執(zhí)行光照計算
}
else  // 否則，使用環(huán)境光兰英，讓場景在聚光之外時不至于完全黑暗
  color = vec4(light.ambient * vec3(texture(material.diffuse, TexCoords)), 1.0);

我們首先計算了lightDir和取反的direction向量（取反的是因為我們想讓向量指向光源而不是從光源出發(fā)）之間的點(diǎn)積撇叁。記住要對所有的相關(guān)向量標(biāo)準(zhǔn)化。

你可能奇怪為什么在if條件中使用的是 > 符號而不是 < 符號畦贸。theta不應(yīng)該比光的切光角更小才是在聚光內(nèi)部嗎陨闹？這并沒有錯，但不要忘記角度值現(xiàn)在都由余弦值來表示的薄坏。一個0度的角度表示的是1.0的余弦值趋厉，而一個90度的角度表示的是0.0的余弦值，你可以在下圖中看到：

你現(xiàn)在可以看到胶坠，余弦值越接近1.0君账，它的角度就越小。這也就解釋了為什么theta要比切光值更大了涵但。切光值目前設(shè)置為12.5的余弦杈绸，約等于0.9978，所以在0.9979到1.0內(nèi)的theta值才能保證片段在聚光內(nèi)矮瘟，從而被照亮瞳脓。

運(yùn)行程序劫侧，你將會看到一個聚光写妥，它僅會照亮聚光圓錐內(nèi)的片段珍特。看起來像是這樣的：

你可以在這里獲得全部源碼嗜桌。

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb_image.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    // build and compile our shader zprogram
    // ------------------------------------
    Shader lightingShader("5.3.light_casters.vs", "5.3.light_casters.fs");
    Shader lampShader("5.3.lamp.vs", "5.3.lamp.fs");

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        // positions          // normals           // texture coords
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f
    };
    // positions all containers
    glm::vec3 cubePositions[] = {
        glm::vec3( 0.0f,  0.0f,  0.0f),
        glm::vec3( 2.0f,  5.0f, -15.0f),
        glm::vec3(-1.5f, -2.2f, -2.5f),
        glm::vec3(-3.8f, -2.0f, -12.3f),
        glm::vec3( 2.4f, -0.4f, -3.5f),
        glm::vec3(-1.7f,  3.0f, -7.5f),
        glm::vec3( 1.3f, -2.0f, -2.5f),
        glm::vec3( 1.5f,  2.0f, -2.5f),
        glm::vec3( 1.5f,  0.2f, -1.5f),
        glm::vec3(-1.3f,  1.0f, -1.5f)
    };
    // first, configure the cube's VAO (and VBO)
    unsigned int VBO, cubeVAO;
    glGenVertexArrays(1, &cubeVAO);
    glGenBuffers(1, &VBO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindVertexArray(cubeVAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    // second, configure the light's VAO (VBO stays the same; the vertices are the same for the light object which is also a 3D cube)
    unsigned int lightVAO;
    glGenVertexArrays(1, &lightVAO);
    glBindVertexArray(lightVAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    // note that we update the lamp's position attribute's stride to reflect the updated buffer data
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // load textures (we now use a utility function to keep the code more organized)
    // -----------------------------------------------------------------------------
    unsigned int diffuseMap = loadTexture(FileSystem::getPath("resources/textures/container2.png").c_str());
    unsigned int specularMap = loadTexture(FileSystem::getPath("resources/textures/container2_specular.png").c_str());

    // shader configuration
    // --------------------
    lightingShader.use();
    lightingShader.setInt("material.diffuse", 0);
    lightingShader.setInt("material.specular", 1);


    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // be sure to activate shader when setting uniforms/drawing objects
        lightingShader.use();
        lightingShader.setVec3("light.position", camera.Position);
        lightingShader.setVec3("light.direction", camera.Front);
        lightingShader.setFloat("light.cutOff", glm::cos(glm::radians(12.5f)));
        lightingShader.setVec3("viewPos", camera.Position);

        // light properties
        lightingShader.setVec3("light.ambient", 0.1f, 0.1f, 0.1f);
        // we configure the diffuse intensity slightly higher; the right lighting conditions differ with each lighting method and environment.
        // each environment and lighting type requires some tweaking to get the best out of your environment.
        lightingShader.setVec3("light.diffuse", 0.8f, 0.8f, 0.8f);
        lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);
        lightingShader.setFloat("light.constant", 1.0f);
        lightingShader.setFloat("light.linear", 0.09f);
        lightingShader.setFloat("light.quadratic", 0.032f);

        // material properties
        lightingShader.setFloat("material.shininess", 32.0f);

        // view/projection transformations
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        lightingShader.setMat4("projection", projection);
        lightingShader.setMat4("view", view);

        // world transformation
        glm::mat4 model;
        lightingShader.setMat4("model", model);

        // bind diffuse map
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, diffuseMap);
        // bind specular map
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, specularMap);

        // render containers
        glBindVertexArray(cubeVAO);
        for (unsigned int i = 0; i < 10; i++)
        {
            // calculate the model matrix for each object and pass it to shader before drawing
            glm::mat4 model;
            model = glm::translate(model, cubePositions[i]);
            float angle = 20.0f * i;
            model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
            lightingShader.setMat4("model", model);

            glDrawArrays(GL_TRIANGLES, 0, 36);
        }


        // again, a lamp object is weird when we only have a spot light, don't render the light object
        // lampShader.use();
        // lampShader.setMat4("projection", projection);
        // lampShader.setMat4("view", view);
        // model = glm::mat4();
        // model = glm::translate(model, lightPos);
        // model = glm::scale(model, glm::vec3(0.2f)); // a smaller cube
        // lampShader.setMat4("model", model);

        // glBindVertexArray(lightVAO);
        // glDrawArrays(GL_TRIANGLES, 0, 36);


        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteVertexArrays(1, &lightVAO);
    glDeleteBuffers(1, &VBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}

但這仍看起來有些假悯辙，主要是因為聚光有一圈硬邊针贬。當(dāng)一個片段遇到聚光圓錐的邊緣時桦他，它會完全變暗，沒有一點(diǎn)平滑的過渡垃瞧。一個真實(shí)的聚光將會在邊緣處逐漸減少亮度脉幢。

平滑/軟化邊緣

為了創(chuàng)建一種看起來邊緣平滑的聚光嫌松，我們需要模擬聚光有一個內(nèi)圓錐(Inner Cone)和一個外圓錐(Outer Cone)液走。我們可以將內(nèi)圓錐設(shè)置為上一部分中的那個圓錐育灸，但我們也需要一個外圓錐，來讓光從內(nèi)圓錐逐漸減暗瓦哎，直到外圓錐的邊界。

為了創(chuàng)建一個外圓錐犯助，我們只需要再定義一個余弦值來代表聚光方向向量和外圓錐向量（等于它的半徑）的夾角剂买。然后，如果一個片段處于內(nèi)外圓錐之間坐慰，將會給它計算出一個0.0到1.0之間的強(qiáng)度值结胀。如果片段在內(nèi)圓錐之內(nèi)糟港，它的強(qiáng)度就是1.0，如果在外圓錐之外強(qiáng)度值就是0.0耸别。

我們可以用下面這個公式來計算這個值：

這里?(Epsilon)是內(nèi)（?）和外圓錐（γ）之間的余弦值差（?=??γ）慈迈。最終的I值就是在當(dāng)前片段聚光的強(qiáng)度痒留。

很難去表現(xiàn)這個公式是怎么工作的，所以我們用一些實(shí)例值來看看：

你可以看到恤磷，我們基本是在內(nèi)外余弦值之間根據(jù)θθ插值扫步。如果你仍不明白發(fā)生了什么，不必?fù)?dān)心游岳，只需要記住這個公式就好了吭历，在你更聰明的時候再回來看看。

我們現(xiàn)在有了一個在聚光外是負(fù)的朗若，在內(nèi)圓錐內(nèi)大于1.0的哭懈，在邊緣處于兩者之間的強(qiáng)度值了遣总。如果我們正確地約束(Clamp)這個值容达，在片段著色器中就不再需要if-else了花盐，我們能夠使用計算出來的強(qiáng)度值直接乘以光照分量：

float theta     = dot(lightDir, normalize(-light.direction));
float epsilon   = light.cutOff - light.outerCutOff;
float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);    
...
// 將不對環(huán)境光做出影響，讓它總是能有一點(diǎn)光
diffuse  *= intensity;
specular *= intensity;
...

注意我們使用了clamp函數(shù)熙揍，它把第一個參數(shù)約束(Clamp)在了0.0到1.0之間诈嘿。這保證強(qiáng)度值不會在[0, 1]區(qū)間之外淳梦。

確定你將outerCutOff值添加到了Light結(jié)構(gòu)體之中爆袍，并在程序中設(shè)置它的uniform值弦疮。下面的圖片中胁塞，我們使用的內(nèi)切光角是12.5，外切光角是17.5：

啊扰才，這樣看起來就好多了衩匣。稍微對內(nèi)外切光角實(shí)驗一下生百，嘗試創(chuàng)建一個更能符合你需求的聚光置侍。你可以在這里找到程序的源碼蜡坊。

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb_image.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path);
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    // build and compile our shader zprogram
    // ------------------------------------
    Shader lightingShader("5.4.light_casters.vs", "5.4.light_casters.fs");
    Shader lampShader("5.4.lamp.vs", "5.4.lamp.fs");

    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    float vertices[] = {
        // positions          // normals           // texture coords
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f
    };
    // positions all containers
    glm::vec3 cubePositions[] = {
        glm::vec3( 0.0f,  0.0f,  0.0f),
        glm::vec3( 2.0f,  5.0f, -15.0f),
        glm::vec3(-1.5f, -2.2f, -2.5f),
        glm::vec3(-3.8f, -2.0f, -12.3f),
        glm::vec3( 2.4f, -0.4f, -3.5f),
        glm::vec3(-1.7f,  3.0f, -7.5f),
        glm::vec3( 1.3f, -2.0f, -2.5f),
        glm::vec3( 1.5f,  2.0f, -2.5f),
        glm::vec3( 1.5f,  0.2f, -1.5f),
        glm::vec3(-1.3f,  1.0f, -1.5f)
    };
    // first, configure the cube's VAO (and VBO)
    unsigned int VBO, cubeVAO;
    glGenVertexArrays(1, &cubeVAO);
    glGenBuffers(1, &VBO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glBindVertexArray(cubeVAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    // second, configure the light's VAO (VBO stays the same; the vertices are the same for the light object which is also a 3D cube)
    unsigned int lightVAO;
    glGenVertexArrays(1, &lightVAO);
    glBindVertexArray(lightVAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    // note that we update the lamp's position attribute's stride to reflect the updated buffer data
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // load textures (we now use a utility function to keep the code more organized)
    // -----------------------------------------------------------------------------
    unsigned int diffuseMap = loadTexture(FileSystem::getPath("resources/textures/container2.png").c_str());
    unsigned int specularMap = loadTexture(FileSystem::getPath("resources/textures/container2_specular.png").c_str());

    // shader configuration
    // --------------------
    lightingShader.use();
    lightingShader.setInt("material.diffuse", 0);
    lightingShader.setInt("material.specular", 1);


    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // be sure to activate shader when setting uniforms/drawing objects
        lightingShader.use();
        lightingShader.setVec3("light.position", camera.Position);
        lightingShader.setVec3("light.direction", camera.Front);
        lightingShader.setFloat("light.cutOff", glm::cos(glm::radians(12.5f)));
        lightingShader.setFloat("light.outerCutOff", glm::cos(glm::radians(17.5f)));
        lightingShader.setVec3("viewPos", camera.Position);

        // light properties
        lightingShader.setVec3("light.ambient", 0.1f, 0.1f, 0.1f);
        // we configure the diffuse intensity slightly higher; the right lighting conditions differ with each lighting method and environment.
        // each environment and lighting type requires some tweaking to get the best out of your environment.
        lightingShader.setVec3("light.diffuse", 0.8f, 0.8f, 0.8f);
        lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);
        lightingShader.setFloat("light.constant", 1.0f);
        lightingShader.setFloat("light.linear", 0.09f);
        lightingShader.setFloat("light.quadratic", 0.032f);

        // material properties
        lightingShader.setFloat("material.shininess", 32.0f);

        // view/projection transformations
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
        glm::mat4 view = camera.GetViewMatrix();
        lightingShader.setMat4("projection", projection);
        lightingShader.setMat4("view", view);

        // world transformation
        glm::mat4 model;
        lightingShader.setMat4("model", model);

        // bind diffuse map
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, diffuseMap);
        // bind specular map
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, specularMap);

        // render containers
        glBindVertexArray(cubeVAO);
        for (unsigned int i = 0; i < 10; i++)
        {
            // calculate the model matrix for each object and pass it to shader before drawing
            glm::mat4 model;
            model = glm::translate(model, cubePositions[i]);
            float angle = 20.0f * i;
            model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f));
            lightingShader.setMat4("model", model);

            glDrawArrays(GL_TRIANGLES, 0, 36);
        }

        // again, a lamp object is weird when we only have a spot light, don't render the light object
        // lampShader.use();
        // lampShader.setMat4("projection", projection);
        // lampShader.setMat4("view", view);
        // model = glm::mat4();
        // model = glm::translate(model, lightPos);
        // model = glm::scale(model, glm::vec3(0.2f)); // a smaller cube
        // lampShader.setMat4("model", model);

        // glBindVertexArray(lightVAO);
        // glDrawArrays(GL_TRIANGLES, 0, 36);


        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &cubeVAO);
    glDeleteVertexArrays(1, &lightVAO);
    glDeleteBuffers(1, &VBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path)
{
    unsigned int textureID;
    glGenTextures(1, &textureID);

    int width, height, nrComponents;
    unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
    if (data)
    {
        GLenum format;
        if (nrComponents == 1)
            format = GL_RED;
        else if (nrComponents == 3)
            format = GL_RGB;
        else if (nrComponents == 4)
            format = GL_RGBA;

        glBindTexture(GL_TEXTURE_2D, textureID);
        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        stbi_image_free(data);
    }
    else
    {
        std::cout << "Texture failed to load at path: " << path << std::endl;
        stbi_image_free(data);
    }

    return textureID;
}

這樣的手電筒/聚光類型的燈光非常適合恐怖游戲汉规，結(jié)合定向光和點(diǎn)光源针史，環(huán)境就會開始被照亮了啄枕。在下一節(jié)的教程中，我們將會結(jié)合我們至今討論的所有光照和技巧智润。

后記

未完窟绷，待續(xù)~~~