I'd say it's a spec bug. ARB_texture_buffer_range should say that the offset should be a multiple of an element size, but it doesn't. The question is, what should the element size be? One component or the whole pixel?
Marek On Wed, Nov 5, 2014 at 9:08 PM, Roland Scheidegger <srol...@vmware.com> wrote: > Trying to fix some bug due to alignment issues in llvmpipe's vertex > fetch, I came across some issue with ARB_texture_buffer_range. > Namely, it looks like the offsets specified there are always in bytes, > regardless the actual format (hence, as long as the > TEXTURE_BUFFER_OFFSET_ALIGNMENT is 1, it would be allowed to have an > offset of 15 bytes for a rgba32f format for instance making all fetches > quite unaligned). > However in gallium we actually have first_elem and last_elem parameters > in the sampler views which are specified in number of elements (so takes > the format into account), which is what d3d10 does and the state tracker > translates to that apparently. IMHO d3d10 makes way more sense there > because that way the necessary alignment scales automatically depending > on the format (so, if the format is 2x16bit for instance you'd need 4 > byte alignment for the offset, and only need 16 bytes alignment for > 4x32bit, ensuring all lookups are always aligned). This means that 15 > byte offset in the example above is completely untranslatable. > But if I see that right, OpenGL doesn't work like that, meaning > effectively gallium drivers (and I doubt most other drivers neither) > cannot actually claim to support TEXTURE_BUFFER_OFFSET_ALIGNMENT lower > than 16, even if they'd only need that for 4x32bit formats. Though most > gallium drivers indeed claim 1 right now. > Looks quite messy... > > Roland > _______________________________________________ > mesa-dev mailing list > mesa-dev@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/mesa-dev _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
