[PD] [GEM-dev] gem : using texture for vertex position

[chris clepper]

You are most likely turning on software rendering by accessing the texture
in the vertex shader.

Textures are uploaded as 8 bit per component which is the standard for
images and video.  Changing this to 32 bit floats is extremely inefficient.
There might be a way to specify the GPU storage to be 32 bit float, but
typically the driver would do the conversion slowly and not the GPU.

Render to texture using gemframebuffer with a 'format FLOAT' message will
give a float texture to read from in the shaders.  I see that you filed a
bug that this object does not work on your machine though.  Maybe you can
try another?

You could try changing the code in pix_texture and recompiling.  Change the
format from GL_UNSIGNED_BYTE to GL_FLOAT to see if that works and speeds it
up.  The uploaded texture will not contain the right values since the GPU
expects a float and the image is still 8 bit.

I probably won't have time to work on this for a few weeks, but I want to
get the framebuffer working better.

On 9/9/07, cyrille henry <cyrille.henry at la-kitchen.fr> wrote:
>
> hello,
>
> i'm tring to do more physics on the GPU, and i'm facing some problems.
> simulation results can be compute on texture (just like the wave example i
> send month ago), so now i'd like to use this texture to move vertex.
>
> if i acces to a texture with a vertex shader just like on a fragment
> shader, then it's very slow.
> (cpu is at 100%)
>
> i found that :
> "vertex textures must be 32-bit-per-component textures, floating point,
> and they can't use any filtering mode except nearest filtering."
>
> i tryed "quality 0" to pix_texture in order to have the nearest filtering
> mode, but i'm not sure about the 32 bit per component texture.
> is it the default on Gem?
> if no, is it possible to change it?
>
> anyone already have an exemple how to use a texture to displace vertex?
>
>
> thanks
>
> cyrille
>
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