Fwd: Wined3d/OpenGL question

[James Trotter]

---------- Forwarded message ----------
From: James Trotter 
Date: Apr 4, 2006 8:16 PM
Subject: Re: Wined3d/OpenGL question
To: Jason Green

On 4/4/06, Jason Green  wrote:
> I may be barking up the wrong tree here, but I'm trying to debug the
> cause of a 502 error ( GL_INVALID_OPERATION ) from glDrawElements() in
> drawprim.c (line 1251).  This is for Civilization 4 using both
> hardware vertex & pixel shaders.  I've only noticed this error when it
> is passed GL_TRIANGLES with a large number of vertices.
>
> Here's a sample output with a little extra debugging info, and cleaned
> up a little:
>
> trace:d3d_draw:primitiveToGl TRIANGLES
> trace:d3d_draw:drawPrimitiveDrawStrided begin number of indices6144,
> number of vertices1156
> trace:d3d_draw:drawPrimitiveDrawStrided end number of indices6144,
> number of vertices1156
> ...
> trace:d3d_draw:drawPrimitiveDrawStrided Using pixel shader
> trace:d3d_draw:drawPrimitiveDrawStrided
> glBindProgramARB(GL_FRAGMENT_PROGRAM_ARB, pixelShader->prgId); call ok
> drawprim.c / 1846
> trace:d3d_draw:drawPrimitiveDrawStrided
> glEnable(GL_FRAGMENT_PROGRAM_ARB); call ok drawprim.c / 1850
> trace:d3d_draw:drawStridedFast (0x7fd98890) : glElements(4, 6144, 0, ...)
> fixme:d3d_draw:drawStridedFast >>>>>>>>>>>>>>>>> 502 from
> glDrawRangeElements @ drawprim.c / 1251
>
> Often, a series of these errors will result in an unhandled exception
> in libglcore.so.1 (nvidia binary 8178 driver for a 6600GT, 2.6.16.1
> kernel).
>
> I read up on the glDrawElements() function and it refered to the
> GetIntegerv() function for GL_MAX_ELEMENTS_VERTICES.   When I call
> that function, it returns 4096, and the number of vertices that it's
> trying to pass is larger than that.  I've tried doing a min() of the
> max and the actual # of vertices, but the results are the same.
>
> So, the question is:  Could this be one of the causes of the graphical
> glitches I'm seeing?  I can toy around with these functions all day,
> but I don't really understand them all that well.  Does that routine
> need to be reworked to split up a D3DPT_TRIANGLELIST into multiple
> calls if the calculated number of vertices/indices is too high for the
> user's graphics card?  Or, am I way off base thinking this has any
> bearing on my real issues?
>
> Thanks,
> Jason

GL_MAX_ELEMENTS_VERTICES and GL_MAX_ELEMENTS_INDICES are just performance
hints, and not actual limits to how many vertices or indices that the driver
can handle.

From
http://pyopengl.sourceforge.net/documentation/manual/glDrawRangeElements.3G....
:

"Implementations denote recommended maximum amounts of vertex and index
data, which may be queried by calling glGet with argument
GL_MAX_ELEMENTS_VERTICES and GL_MAX_ELEMENTS_INDICES. If end - start + 1 is
greater than the value of GL_MAX_ELEMENTS_VERTICES, or if count is greater
than the value of GL_MAX_ELEMENTS_INDICES, then the call may operate at
reduced performance. There is no requirement that all vertices in the range
[start,end] be referenced. However, the implementation may partially process
unused vertices, reducing performance from what could be achieved with an
optimal index set."

Also,

"GL_INVALID_OPERATION is generated if glDrawRangeElements is executed
between the execution of glBegin and the corresponding glEnd."