Tracking down a native crash in glDrawArrays

OpenGL Development
#1

I’m getting a native crash in glDrawArrays and was wondering if anyone had any cunning ways of tracking it down.

It only appears to happen when I mix both textured and non-textured geometry in one frame (sprites and wireframe drawing). Individually the two shaders work fine, but not when both are used.

All params to draw arrays look fine - a reasonable amount of vertices (2804 vertices taking 67296 bytes). Changing the order of drawing still crashes, and trying to bind fixed-function at the end of the frame still causes a crash.

All drawing is regular vertex arrays, no VBOs. No FBOs either. I suspect I’ve left some dangling pointer or something inside GL state, but can’t figure out what it could be. Any suggestions for what to look at?

#2

Maybe, in the case were you have mixed textured/untextured geometry, you accidently leave texcoord arrays enabled when not specifying them, for the untextured geometry.

#3

Hmm, possibly. I’m actually using ARBVertexProgram.glEnableVertexAttribArrayARB() rather than using the fixed function tex coord/etc. arrays, but I might still have something active…

#4

Ah, I think I have it: http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=15603

glEnableVertexAttribArrayARB is global state, not per-active-program state, which is what I was thinking. Going to be awkward to fix without reworking the whole structure though. :S

#5

That clearly explains the crashes. It’s quite an important fix too, so you’d have to rewrite the whole structure anyway.

#6

The way “around this” is to use VAOs, which encapsulate these attributes in a bindable object.

#7

Yeah, part of my problem was that I designed this stuff with VBOs and VAOs in mind, but I haven’t got around to doing anything fancier than regular vertex arrays. Still, it was an easy fix in the end.

How widespread are VAOs these days? I suspect that since they’re GL3.0 I probably can’t rely on them existing so I’ll still need a fallback path.

#8

The extension is supported by DirectX 9 cards, which equals a Geforce 6000 series card. That was 7 generations ago.
Source: http://feedback.wildfiregames.com/report/opengl/feature/GL_ARB_vertex_array_object

#9

FYI: VBOs are just like VAs, with regards to the array states being global.