原文：https://developer.android.com/training/graphics/opengl/touch.html#angle
示例代碼
Making objects move according to a preset program like the rotating triangle is useful for getting some attention, but what if you want to have users interact with your OpenGL ES graphics? The key to making your OpenGL ES application touch interactive is expanding your implementation of GLSurfaceView to override the onTouchEvent() to listen for touch events.
讓一個三角形轉(zhuǎn)動看起來很屌，但是怎么才能讓用戶和OpenGL ES圖形進(jìn)行交互？方法就是重寫GLSurfaceView的onTouchEvent() 方法來處理用戶點擊事件石洗。
This lesson shows you how to listen for touch events to let users rotate an OpenGL ES object.
這一節(jié)講解如何根據(jù)點擊事件來旋轉(zhuǎn)OpenGL ES圖形吱殉。
Setup a Touch Listener
設(shè)置點擊監(jiān)聽器
In order to make your OpenGL ES application respond to touch events, you must implement the onTouchEvent() method in your GLSurfaceView class. The example implementation below shows how to listen for MotionEvent.ACTION_MOVE events and translate them to an angle of rotation for a shape.
為了讓OpenGL ES應(yīng)用能夠響應(yīng)你的點擊事件目溉，你必須實現(xiàn)GLSurfaceView的onTouchEvent()方法。下面的例子展示如何把MotionEvent.ACTION_MOVE事件轉(zhuǎn)化為圖形旋轉(zhuǎn)的角度。
private final float TOUCH_SCALE_FACTOR = 180.0f / 320;
private float mPreviousX;
private float mPreviousY;
@Override
public boolean onTouchEvent(MotionEvent e) {
// MotionEvent reports input details from the touch screen
// and other input controls. In this case, you are only
// interested in events where the touch position changed.
float x = e.getX();
float y = e.getY();
switch (e.getAction()) {
case MotionEvent.ACTION_MOVE:
float dx = x - mPreviousX;
float dy = y - mPreviousY;
// reverse direction of rotation above the mid-line
if (y > getHeight() / 2) {
dx = dx * -1 ;
}
// reverse direction of rotation to left of the mid-line
if (x < getWidth() / 2) {
dy = dy * -1 ;
}
mRenderer.setAngle(
mRenderer.getAngle() +
((dx + dy) * TOUCH_SCALE_FACTOR));
requestRender();
}
mPreviousX = x;
mPreviousY = y;
return true;
}
Notice that after calculating the rotation angle, this method calls requestRender() to tell the renderer that it is time to render the frame. This approach is the most efficient in this example because the frame does not need to be redrawn unless there is a change in the rotation. However, it does not have any impact on efficiency unless you also request that the renderer only redraw when the data changes using the setRenderMode() method, so make sure this line is uncommented in the renderer:
注意，每次計算好角度之后都要調(diào)用一次requestRender() 方法告訴renderer該重繪了依鸥。這是最高效的方法，因為沒有改變角度就沒有必要重繪悼沈。（下面這句不翻了贱迟，看不懂??）確保setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
public MyGLSurfaceView(Context context) {
...
// Render the view only when there is a change in the drawing data
setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY);
}
Expose the Rotation Angle
傳遞旋轉(zhuǎn)角度
The example code above requires that you expose the rotation angle through your renderer by adding a public member. Since the renderer code is running on a separate thread from the main user interface thread of your application, you must declare this public variable as volatile. Here is the code to declare the variable and expose the getter and setter pair:
上面的代碼還需要你在renderer中建立一個public變量姐扮，用來傳遞旋轉(zhuǎn)角度。因為renderer的代碼是在另一個線程中運行衣吠，而不是UI線程茶敏，所以這個變量必須設(shè)為volatile(UI線程中獲取了旋轉(zhuǎn)角度，繪制線程中調(diào)用這個角度）缚俏。如下：
public class MyGLRenderer implements GLSurfaceView.Renderer {
...
public volatile float mAngle;
public float getAngle() {
return mAngle;
}
public void setAngle(float angle) {
mAngle = angle;
}
}
Apply Rotation
旋轉(zhuǎn)
To apply the rotation generated by touch input, comment out the code that generates an angle and add mAngle, which contains the touch input generated angle:
加上以下代碼惊搏，將點擊產(chǎn)生的角度加到矩陣中。
public void onDrawFrame(GL10 gl) {
...
float[] scratch = new float[16];
// Create a rotation for the triangle
// long time = SystemClock.uptimeMillis() % 4000L;
// float angle = 0.090f * ((int) time);
Matrix.setRotateM(mRotationMatrix, 0, mAngle, 0, 0, -1.0f);
// Combine the rotation matrix with the projection and camera view
// Note that the mMVPMatrix factor *must be first* in order
// for the matrix multiplication product to be correct.
Matrix.multiplyMM(scratch, 0, mMVPMatrix, 0, mRotationMatrix, 0);
// Draw triangle
mTriangle.draw(scratch);
}
When you have completed the steps described above, run the program and drag your finger over the screen to rotate the triangle:
完成之后忧换，運行程序恬惯，用手指轉(zhuǎn)動三角形。
