GLES20.glReadPixels在Android中全为零 [英] GLES20.glReadPixels gets all zero in android

问题描述

大家好，我希望屏幕可以显示我们触摸过的像素的颜色，然后按如下所示使用GLES20.glReadPixels.如logcat所示，无论我在哪里单击，它始终读取0 0 0 0.我还根据屏幕的宽度和高度更改了索引，但仍然得到全零.我知道这样做应该很容易，但是我真的不知道如何解决它.有人可以帮我吗?非常感谢！

Hello guys~I want the screen can show what color of the pixel we touched, then I use GLES20.glReadPixels as follow. As shown on logcat, it always reads 0 0 0 0 no matter where I clicked. I also changed index according to width and height of the screen, but still getting all zeros. I know it should be very easy to do that, but I really have no idea on how to solve it. Can anybody give me a hand? Thank you so much!

public String getFace(float angleX, float angleY, float positionX, float positionY){
    String toast = "other";
    int tempX = Math.round(positionX);
    int tempY = Math.round(positionY);
    ByteBuffer ss = ByteBuffer.allocate(4);
    ss.order(ByteOrder.nativeOrder());
    GLES20.glFlush();

    //Get Screen's width and height
    DisplayMetrics displaymetrics = new DisplayMetrics();
    ((Activity) getContext()).getWindowManager()
            .getDefaultDisplay()
            .getMetrics(displaymetrics);
    int height = displaymetrics.heightPixels;
    int width = displaymetrics.widthPixels;
    int X = tempX;
    int Y = height-tempY;

  //Here it's
    GLES20.glReadPixels(X, Y, 1, 1, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, ss);
    byte b[] = new byte[4];
    ss.get(b);
    String key = "" + b[0] + " " + b[1] + " " + b[2] + " " + b[3];
    Log.d("Color: ", key);
    ss.rewind();
    Log.d("DEBUG", "X:"+ X + " Y:" + Y);
    Log.d("DEBUG", "w:"+ width + " h:" + height);
        if (key = ' 1 0 0 1') {
            toast = "Face Red";
        } else {
            toast = "other";
        }

    return toast;
}

推荐答案

现在，我知道问题出在哪里！由于我有一个MyRenderer.java，它是当前的OpenGL上下文.而且glReadPixels()仅在当前存在OpenGL上下文的情况下有效！上面的代码在我的MyGLSurfaceView.java中，该代码负责辅助线程，因此这就是glReadPixels()不读取任何内容的原因.

Now, I know where the problem is! Since I have a MyRenderer.java which is the current OpenGL context. And glReadPixels() only works if there is a current OpenGL context! Code above was in my MyGLSurfaceView.java which take care of a secondary thread, so that's why glReadPixels() reads nothing.

解决方案使用的是GLSurfaceView.queueEvent()，它可以转发到渲染线程.我们现在可以在Renderer.java中编写glReadPixels()，并从中读取结果.

Solution is using the GLSurfaceView.queueEvent() which forward to rendering thread. We can write glReadPixels() in Renderer.java now, and read result from that.

这是一个示例，引用了在此处输入链接描述

This is an example referred to enter link description here

 class MyGLSurfaceView extends GLSurfaceView {

 private MyRenderer mMyRenderer;

 public void start() {
     mMyRenderer = ...;
     setRenderer(mMyRenderer);
 }

 public boolean onKeyDown(int keyCode, KeyEvent event) {
     if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
         queueEvent(new Runnable() {
             // This method will be called on the rendering
             // thread:
             public void run() {
                 mMyRenderer.handleDpadCenter();
             }});
         return true;
     }
     return super.onKeyDown(keyCode, event);
 }
 }

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