Help end child hunger
Jan 022012

Very Simple OpenGL Information Lib – OpenGL has a rich set of functions to query its state. It is possible to get information on just about anything, from which shaders are attached to a program, to the values of uniforms, or the properties of the textures currently bound.

However, it is also true, that to get some of this information a lot of code is required. When debugging, we end up writing code to access this and that information over and over again.

This lib attempts to provide all the information with a minimal effort to the developer, for textures, buffers, GLSL programs, shaders, and variables, and a few more items.

Dec 152011

One of the bugs reported in here has been corrected. The uniform buffer data size is now reported correctly.

The other two bugs remain, unfortunately. Querying the primitive counter still gives zero, and glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB) still crashes the application.

Dec 092011

VSML has been renamed to VSMathLib. Too many libs in the pipeline to keep naming them with a single letter :-)

The M stood for Matrix, yet as now the library also contains vector operations, I think the new name fits better with the content.

Another addition is the availability of the normal and projection-view-model matrices. These are commonly used in shaders, and it doesn’t make sense to keep computing it for every vertex.

Finally, the lib now works with the VSShaderLib to provide a more general method for uniform variable settings.

Bug reports are most welcome.

Dec 052011

Shaders are the core of the rendering process. OpenGL core profile requires us to provide our own shaders, no more fixed function.

Using shaders means more flexibility, but it also implies more work. This is where this lib steps in.

VSShaderLib was designed to make our life easier. It allows to create programs, load shaders from files, associate vertex attribute names with locations, and work with uniforms, including uniforms in named blocks. It also provides access to the info logs.

Nov 072011

I don’t know where to put this. I’ve tried the AMD forum but got no reply. So here goes:

I’ve only tested this on Windows 7 64 bits. Anyone with different/same results on same or other systems?

 – ARB Debug Output Extension

When not in debug mode the following instruction causes an Access Violation in Visual Studio:


This only occurs when not in Debug OpenGL context  and it does not cause any problem with nVidia hardware.

I’ve not tried it with Linux yet.


– Uniform Buffers

Consider a uniform block declared as follows:

layout (std140) uniform Matrices {

	mat4 modelviewMatrix;
	mat4 projModelViewMatrix;
	mat3 normalMatrix[2];

This is what I get when I use glGetActiveUniformsiv to retrieve info on the block:

Matrices, Binding: 2 Datasize: 320 ActiveUniforms: 3
Referenced by: TessEval  Shader(s)
modelviewMatrix 1 16 mat4 0
normalMatrix 2 16 mat3 128
projModelViewMatrix 1 16 mat4 64

The data for each uniform is size, matrix stride, type and offset.

My problem lies with the size of the buffer. AMD’s driver claims, as shown above, that the size is 320, but in reality it is 224 (nVidia reports the right value), considering the reported matrix stride of 16. The math is pretty simple:

16×4 = 64 bytes for each 4×4 matrix times 2 = 128

16×3 = 48 bytes for each 3×3 matrix times 2 = 96

Total = 128 + 96 = 224.

Strangely enough,  if I define the normalMatrix as an array with 3 mat3 (so one more than previously), I get a reported data size of 464.

I’ve tested several possibilities to set one of the mat3 without success. With nVidia it works OK . The only difference in the information reported, besides the data size, is the name of the normalMatrix uniform, that nVidia chooses to call it normalMatrix[0].


– Querying the primitive counter

I always get zero! Again works nicely in nVidia.