Hi,
[email protected] wrote:
Hi everyone,
I would like to use osg PPU to compute very accurate data, about ten
number behind the comma, to avoid numerical errors.
I don't think you will reach this with single precision floating point.
So I used 32 bits textures for the render to texture :
texture2D->setInternalFormat(GL_RGBA32F_ARB);
texture2D->setSourceFormat(GL_RGBA);
texture2D->setSourceType(GL_FLOAT);
texture2D->setWrap(osg::Texture2D::WRAP_S,osg::Texture2D::CLAMP_TO_BORDER);
texture2D->setWrap(osg::Texture2D::WRAP_T,osg::Texture2D::CLAMP_TO_BORDER);
texture2D->setWrap(osg::Texture2D::WRAP_R,osg::Texture2D::CLAMP_TO_BORDER);
texture2D->setFilter(osg::Texture2D::MIN_FILTER, osg::Texture2D::NEAREST);
texture2D->setFilter(osg::Texture2D::MAG_FILTER,osg::Texture2D::NEAREST);
But I noticed, by exemple, when I put the value 0.012024048 in one
shader (gl_FragColor = vec(0.012024048, 0.012024048, 0.012024048, 1.0);),
the value read in the next shader becomes 0.012023926.
I checked the values twice, once with the glsl Devil debugger, once with
an UnitOutCapture.
What video card do you have?
Is there a way to have more precision for my data ?
Two options maybe:
1) Double precision float path. You will have to first get hardware that
supports it and I think you will probably have to look at CUDA. I'm not
sure which cards do this, have a look at the CUDA documentation. Other
problem is that I don't know of double precision floating point texture
formats that will work easily with OSG.
2) If your data can be split (ito precision) across multiple colour
channels you might be able to do some arithmetic in shaders yourself.
See also here:
http://www.gpgpu.org/wiki/FAQ
I don't have much experience with either of 2 options above, so if
someone else has some concrete info I would also be interested.
rgds
jp
Thanks in advance,
Josselin.
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