Re: [Mesa3d-dev] Floating point texture support (enabling GPGPU applications)

[Brian P. <br...@vm...>]

Christian Buchner wrote:
> Hi,
> 
> I've been looking into using 32 bit floating point textures as render
> targets ( for example by creating an FBO with a 32 bit RGBA texture ).
> On further research I found that the extension "ARB_texture_float" is
> not currently provided by Mesa. I do run Mesa HEAD using a GEM enabled
> Linux kernel and the latest i915 XOrg and DRM drivers (all HEAD
> releases).
> 
> Are there any plans to support floating point textures in Mesa in the
> future? These are really important for GPGPU (general purpose
> computing) because in combination with fragment shaders these can be
> used to perform single precision floating point arithmetics.
> 
> After enabling the extension I found that the i915 DRI driver was not
> yet able to map floating point texture types to a hardware ID. I know
> that the Intel 950GMA core is well capable of using floating point
> textures, as for example on an Intel Mac Mini running MAC OS X Leopard
> I am successfully running fragment shaders on these textures.
> 
> So I am having two issues that I would like to resolve
> 
> a) the fact that Mesa doesn't currently support the GL_RGBA32F_ARB
> internalFormat when creating textures (and frame buffer objects)
> 
> b) the i915 driver (and probably all other Mesa DRI drivers for that
> matter) do not yet handle GL_RGBA32F_ARB the texture format.
> 
> I`ve partially solved the first problem by patching Mesa accordingly
> but now I've hit a snag with the DRI driver.
> 
> Looking into the i915_reg.h header file I find references to page
> numbers in some hardware manual, however it is not clearly stated
> which manual was used. There are unfortunately no defines for hardware
> IDs matching floating point textures defined in this header file.
> 
> So I downloaded the 915G and 945GM chipset manuals from the Intel
> developer site, but the page numbers given in the header files do not
> match those I looked up in these Intel documents. Would anyone here
> know which developer manual describes the graphics registers of the
> 950GMA graphics core - in particular for the texture stages? If I can
> get hold of that manual I might try to add the missing texture
> capabilities myself (being a fearless hacker...)
> 
> Is there a separate mailing list for the Intel 3D drivers in Mesa?

If you read the "IP Status" section of the GL_ARB_texture_float spec 
(http://www.opengl.org/registry/specs/ARB/texture_float.txt) you'll see 
the reason why Mesa doesn't support this extension yet.

Perhaps a work-around similar to what's done for s3tc texture 
compression would be the way forward...

-Brian