🚀 go-pugleaf

Shuky Rosinger <rosinger@numbat.cs.rmit.edu.au> writes:

| Hi all,
| 
| I am having a very hard time drawing pixel data with glDrawPixels onto
| an OpenGL scene. I use glDrawPixels with GL_RGB, GL_UNSIGNED_BYTE. The
| image is retrieved with XGetImage.
| 
| The resulting image in the OpenGL scene is somehow not synchronized (has
| the effect of a TV has bad horizontal sync or vertical sync).

A few things to check:

1) Pixel data has a default per-row alignment of 4 bytes; hence RGB data
might be misaligned per-row, giving the image a "sheared" appearence.
Try setting:

	glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

2) The format returned by XGetImage may not be what you expect - always
check the red_mask, green_mask, and blue_mask fields to see the pixel
layout.  You may have to reformat the data.  I would expect a 16-bit
drawable to return data in 2 bytes per pixel, so you'll have to extract
and expand the data to fit unsigned byte RGB format.
--
Michael I. Gold     Silicon Graphics Inc.     http://reality.sgi.com/gold 
And my mama cried,  "Nanook a no no! Don't be a naughty eskimo! Save your
money, don't go to the show!"  Well I turned around and I said, "Ho! Ho!"