On Mon, Apr 19, 2010 at 03:38:54PM +0200, José Fonseca wrote: > On Mon, 2010-04-19 at 06:22 -0700, Keith Whitwell wrote: > > On Mon, 2010-04-19 at 06:07 -0700, Marek Olšák wrote: > > > Unfortunately, this is supported only on r500 (i.e. not r300 nor r400) > > > and only when the DRM version is >=2.3.0 (i.e. kernel 2.6.34). Please, > > > can we make it an optional feature? > > > > Are you sure about this? It seems to be a long-time DX9 (and earlier?) > > requirement. > > > > I'm sure it can be made optional, though - if a state tracker absolutely > > required it & didn't want to implement a workaround, it could just fail > > to initialize on such drivers. > > Positive index bias are trivial to implement on any hardware. > > One way of implementing negative index bias would be by programing the > hardware with an artificially lower offset: > > + - - - - - - - - - - +---------------------+ > : index_bias*stride | real vertex buffer | > + - - - - - - - - - - +---------------------+ > ^ > | > pass this to hardware > > but the hardware would need to have builtin support for vertex buffer > max/min index checking, to ensure only vertices inside the real range > are read. Also, the DRM would need to support these relocation with > negative offsets, and make sure that the start offset doesn't wrap > around vram start. > > If the above doesn't work, then is just a matter of reading the index > buffer, make a copy of with with the right indices and use it instead. > > Actually, a mixture of the above can be used. > > So there is really no excuse to not support this feature unless it is > perceived to be useless. > > A big user of this extension would be wine, but I've checked their > source code and they don't use it yet. Actually, they just set negative > vertex buffers offsets as a unsigned and pray that the two's complement > arithmetic inside the GL driver just works. > > This feature is really used by D3D software, e.g. Google Earth on D3D. > > Jose >
The way we communicate command stream (CS) with the kernel, doesn't allow for negative offset. The positive offset can't still be achieve. Cheers, Jerome _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
