I've built some test files.
The attached archive contains:
- withoutshader.osg: a 20x20x20 3D grid of cubes
- withshader_0.osg: the same grid but with a basic shader in the root
node (no uniforms)
- withshader_1.osg: the same grid but with a basic shader in the root
node (1 uniforms)
- withshader_10.osg: the same grid but with a basic shader in the root
node (10 uniforms)
- withshader_20.osg: the same grid but with a basic shader in the root
node (20 uniforms)
- withshader_30.osg: the same grid but with a basic shader in the root
node (30 uniforms)
- withshader_100.osg: the same grid but with a basic shader in the root
node (100 uniforms)
The uniform are defined in the root node (with the shader).
On my machine (Core2 duo 6400 + GeForce 7900GTX + OSG 1.2):
- withoutshader.osg: 25.7 fps
- withshader_0.osg: 23.2 fps
- withshader_1.osg: 23.1 fps
- withshader_10.osg: 22.3 fps
- withshader_20.osg: 21.2 fps
- withshader_30.osg: 20.1 fps
- withshader_100.osg: 11.7 fps
Lionel Lagarde wrote:
Hi Robert,
The uniform values are not changing per drawables. They are fixed in
the root
state set (it contains also the shader program).
None of the children of the root node define uniforms (nor shader)
But, per-drawable, the PerContextProgram::apply function is called for
each
uniform registered in the root node.
Robert Osfield wrote:
Hi Loinel,
High number of uniforms will be the bottleneck, changing uniforms in
OpenGL is relatively expensive. If you shader parameter various
changing per drawable then use vertex attributes rather than uniforms.
Robert.
On 6/11/07, Lionel Lagarde <[EMAIL PROTECTED]> wrote:
It's seems that nobody has this problem.
High number of drawables + high number of uniforms = bad performances
Lionel Lagarde wrote:
> Hi,
>
> Problem description:
> We have a scene with a lot of drawables (>1500). The stateset of the
> root of the
> scene graph contains a shader program.
>
> When we increase the number of uniform variables used by the shader,
> the application performance drop down.
>
> A little debugging session after, it appears that for each drawable
> that has a stateset
> defined, the uniform variables are applied.
>
> They are not really applied, (their modifiedCount has not changed)
but
> the
> osg::Program::PerContextProgram (line 163) do a "find" on a std::map
> (std::string -> GLint)
> to retrieve the uniform location.
>
> It seems that it is this access to the std::map that cause the
> performance drop.
>
> Does someone has encountered this problem ?
> Is there a way to disable the uniform application for each
drawables ?
>
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> osg-users@openscenegraph.net
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>
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