Display Lists and Not Display Lists

Graphics and GPU Programming Programming

Started by Geometrian July 10, 2007 03:03 PM

6 comments, last by Nathan Baum 16 years, 9 months ago

Geometrian

1,813

Author

July 10, 2007 03:03 PM

Hi, I have some code:

glLoadIdentity()
glTranslatef(-0.129, 0.197, -0.5)
glCallList(4)
glTranslatef(-0.127, 0.0, 0.0)
glColor4f(1.0, 1.0, 1.0, 0.5)
size = 0.008
if timeleft > 19.5:
    timeleft = 19.5
glBegin(GL_QUADS)
glVertex3f(0.0*size, -1.0*size, 0)
glVertex3f(timeleft*size, -1.0*size, 0)
glVertex3f(timeleft*size, 1.0*size, 0)
glVertex3f(0.0*size, 1.0*size, 0)
glEnd()
glColor4f(1.0, 1.0, 1.0, 1.0)

but if I comment out glCallList(4), the quad is not drawn! Why not? Here's the code for display list 4:

size = .01
glGenLists(1)
glNewList(4, GL_COMPILE)
glBindTexture(GL_TEXTURE_2D, textures[0])
glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, selfSurface.get_width(), selfSurface.get_height(), 0,
              GL_RGBA, GL_UNSIGNED_BYTE, selfData )
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)
glBegin(GL_QUADS)
glTexCoord2f(0.0, 0.0); glVertex3f(-12.9636*size, -1.0*size, 0.0)
glTexCoord2f(1.0, 0.0); glVertex3f(12.9636*size, -1.0*size, 0.0)
glTexCoord2f(1.0, 1.0); glVertex3f(12.9636*size, 1.0*size, 0.0)
glTexCoord2f(0.0, 1.0); glVertex3f(-12.9636*size, 1.0*size, 0.0)
glEnd();
glEndList()

[size="1"]And a Unix user said rm -rf *.* and all was null and void...|There's no place like 127.0.0.1|The Application "Programmer" has unexpectedly quit. An error of type A.M. has occurred.
[size="2"]

pieslice

194

July 10, 2007 03:20 PM

Do you mean the latter quad, since commenting out glCallList(4) will of course disable the rendering of the quad you've compiled to the drawlist 4?

If you mean the latter quad, it seems to have no texture coordinates, so you should disable the GL_TEXTURE_2D (I assume you have it enabled since your call list quad has texture coordinates) before rendering it.
When you render the call list quad, the texture coordinate for every vertex of the secondary quad is same which was the last texture coordinate for the call list quad, and if the texturing is enabled the whole quad will be textured with one texel and it becomes visible. If you disable the call list quad, and draw the secondary quad, every texture coordinate will be most likely 0,0 if you haven't set any texture coordinates previously.

Geometrian

1,813

Author

July 10, 2007 03:22 PM

Yes, the latter quad; the one whose drawing code was not commented out.

pieslice

194

July 10, 2007 03:28 PM

See modified post, I tried to figure out something.

Geometrian

1,813

Author

July 10, 2007 03:37 PM

THAT WORKS! Thanks! (Note that one must add "glEnable(GL_TEXTURE_2D)" after the quad has been rendered!) This also fixes some issues I've been having with color.

zix99

205

July 10, 2007 03:40 PM

In creating your list, you are also uploading the date for the texture. You should not be doing this, it will cause speed problems later, and may or may not be causing your current problem.

I think that's your problem. The texture isn't being uploaded (all the calls in the compiling of the display list arent' actually called until you call glCallList, so the texture is never uploaded when you comment out the list call).

Hope that helps
~Zix

[Edited by - zix99 on July 10, 2007 4:40:33 PM]

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Geometrian

1,813

Author

July 10, 2007 04:06 PM

The problem was already solved, but yes, I know what you are talking about. strangely enough, the other way makes it run slower!

Nathan Baum

1,027

July 10, 2007 08:28 PM

Quote:Original post by Geometrian
The problem was already solved, but yes, I know what you are talking about. strangely enough, the other way makes it run slower!

Looks like this depends upon your GL implementation and what you're doing in the display list. On my system, using display lists incurs a slight but constant penalty. Using them for setting up textures is quite a bit slower than just using texture names, but using them for setting up other kinds of state (e.g. matrices, shaders, lighting) is a little bit faster than setting that state up manually, although of course it's faster if you can avoid setting the state at all.

Display Lists and Not Display Lists

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