Question

So my glReadPixel call:

  glPixelStorei(GL_PACK_ALIGNMENT, 1);
  GLfloat lebuf[128 * 128 * 4];
  glReadPixels(0, 0, 128, 128, GL_RGBA, GL_FLOAT, lebuf);

just puts 1.0 values in the lebuf array. This is just after finishing drawing the page, and the resultant result is a “white” image.

checking the GL errors indicate that there’s nothing wrong.

what could have possibly gone wrong?

Answer 1

Make sure glReadBuffer(GL_FRONT) is set before glReadPixels. If it is not, you could be reading from a different buffer, such as the back buffer when double buffering.

And of course, ensure that your capture area – 128×128 – is not all white.