why glReadPixels method always get RGB(0, 0, 0)

Question

I try to implement color picking in Android OpenGL ES.

Here I get the coordinate:

public boolean onTouchEvent(MotionEvent e) {
   float x = e.getX();
   float y = e.getY();
   ...

Here I want to get the pixel information on click:

public void processPick(GL10 gl){
    ByteBuffer pixel = ByteBuffer.allocate(4);
    pixel.order(ByteOrder.nativeOrder());
    gl.glReadPixels((int)clickPosX, (int)clickPosY, 1, 1, GL10.GL_RGB, GL10.GL_UNSIGNED_BYTE, pixel);
    byte[] b = new byte[3];
    pixel.get(b);
    Log.d("buffer", b[0] + ",  "+b[1]+", "+b[2]);
}

But actually I always get RGB(0, 0, 0), what's wrong? How to set color and pick color correctly?

Anyone can help me? Thanks!

Answer 1

Try this: gl.glReadPixels((int)clickPosX, (int)clickPosY, 1, 1, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, pixel); byte[] b = new byte[4];