Taking screenshot of Android OpenGL

Question

Hello,

I'm fighting from some time with taking a screenshot of Android OpenGL.

The code I found is as follows:

nt size = width * height;
    ByteBuffer buf = ByteBuffer.allocateDirect(size * 4);
    buf.order(ByteOrder.nativeOrder());
    glContext.glReadPixels(0, 0, width, height, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, buf);
    int data[] = new int[size];
    buf.asIntBuffer().get(data);
    buf = null;
    Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    bitmap.setPixels(data, size-width, -width, 0, 0, width, height);
    data = null;

    short sdata[] = new short[size];
    ShortBuffer sbuf = ShortBuffer.wrap(sdata);
    bitmap.copyPixelsToBuffer(sbuf);
    for (int i = 0; i < size; ++i) {
        //BGR-565 to RGB-565
        short v = sdata[i];
        sdata[i] = (short) (((v&0x1f) << 11) | (v&0x7e0) | ((v&0xf800) >> 11));
    }
    sbuf.rewind();
    bitmap.copyPixelsFromBuffer(sbuf);

    try {
        FileOutputStream fos = new FileOutputStream("/sdcard/screeshot.png");
        bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
        fos.flush();
        fos.close();
    } catch (Exception e) {
        // handle
    }

I tried also a code from that site link text

In each case the result is a png file which is completely black. I found there is some problem with glReadPixels method but I don't know how to bypass it. Any guidance will very helpfull.

Thank You in advance, Gordon

Answer 1

Got it!

My mistake was that I was remembering GL context in the class variable. In order to take a screenshot I have to use the gl context passed to the OnDraw in the class implementing GLSurfaceView.Renderer interface. I simply use my code in the "if" clause and everything works as expected. Hope that remark would help anyone.

Best regards, Gordon