On 10/26/2013 01:33 PM, Kenneth Graunke wrote:
> ARB_transform_feedback3 allows applications to insert blank space
> between interleaved varyings by adding fake 1, 2, 3, or 4-component
> varyings named gl_SkipComponents[1234].
>
> Mesa's core data structures don't explicitly track these, instead simply
> tracking the buffer offset for each real varying. If there is padding
> due to gl_SkipComponents, these will not be contiguous.
>
> Our hardware takes the specification quite literally. Instead of
> specifying offsets for each varying, it assumes they're all contiguous
> and requires you to program fake varyings for each "hole".
>
> This patch adds support for emitting SO_DECL structures for these holes.
> Although we've lost the information about exactly how the application
> specified their padding (i.e. gl_SkipComponents2, gl_SkipComponents2
> vs. a single gl_SkipComponents4), it shouldn't matter. We just need to
> emit the right amount of space. This patch emits the minimal number of
> hole SO_DECL structures.
>
> Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.roman...@intel.com>
> ---
> src/mesa/drivers/dri/i965/gen7_sol_state.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/gen7_sol_state.c
> b/src/mesa/drivers/dri/i965/gen7_sol_state.c
> index b9debdb..6be658f 100644
> --- a/src/mesa/drivers/dri/i965/gen7_sol_state.c
> +++ b/src/mesa/drivers/dri/i965/gen7_sol_state.c
> @@ -140,9 +140,28 @@ gen7_upload_3dstate_so_decl_list(struct brw_context *brw,
> SO_DECL_REGISTER_INDEX_SHIFT;
> decl |= component_mask << SO_DECL_COMPONENT_MASK_SHIFT;
>
> - /* This assert should be true until GL_ARB_transform_feedback_instanced
> - * is added and we start using the hole flag.
> + /* Mesa doesn't store entries for gl_SkipComponents in the Outputs[]
> + * array. Instead, it simply increments DstOffset for the following
> + * input by the number of components that should be skipped.
> + *
> + * Our hardware is unusual in that it requires us to program SO_DECLs
> + * for fake "hole" components, rather than simply taking the offset
> + * for each real varying. Each hole can have size 1, 2, 3, or 4; we
> + * program as many size = 4 holes as we can, then a final hole to
> + * accomodate the final 1, 2, or 3 remaining.
> */
> + int skip_components =
> + linked_xfb_info->Outputs[i].DstOffset - next_offset[buffer];
> +
> + next_offset[buffer] += skip_components;
> +
> + while (skip_components >= 4) {
> + so_decl[decls++] = SO_DECL_HOLE_FLAG | 0xf;
> + skip_components -= 4;
> + }
> + if (skip_components > 0)
> + so_decl[decls++] = SO_DECL_HOLE_FLAG | ((1 << skip_components) - 1);
> +
> assert(linked_xfb_info->Outputs[i].DstOffset == next_offset[buffer]);
>
> next_offset[buffer] += components;
>
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