[Mesa-dev] [PATCH 00/10] glsl: Implement varying packing.

Paul Berry stereotype441 at gmail.com
Wed Dec 12 10:51:08 PST 2012

On 12 December 2012 10:21, Paul Berry <stereotype441 at gmail.com> wrote:

> On 12 December 2012 09:09, Marek Olšák <maraeo at gmail.com> wrote:
>> R300 and R400 support 4 texture indirections (as defined by
>> ARB_fragment_program). Adding ALU instructions before the first TEX
>> instruction increases the number of texture indirections by 1, which
>> might make some shaders not be executable on the hardware at all.
>> I think this optimization should be disabled on drivers where the
>> texture indirection limit is too low.
>> Marek
> Hmm, I see.  Follow up question:
> My patches implement varying packing in two ways: (a) within a composite
> varying (such as a matrix or array varying) and (b) between varyings.
> Disabling (b) on some drivers would be pretty simple.  Disabling (a) would
> be more of a pain, because it would require there to be two paths to handle
> transform feedback, one that understands how to do feedback for packed
> varyings, and one that understands how to do feedback for unpacked
> varyings.  I was kind of hoping we could avoid that.  Do you think it would
> be adequate to disable just (b) on R300 and R400, or do you think we have
> to disable both (a) and (b) on R300 and R400?

Come to think of it, do R300 and R400 support transform feedback at all?
If not, then this would be a lot easier.
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