[Mesa-dev] [PATCH V2 07/12] i965: Add FS backend for builtin gl_SamplePosition

[Eric Anholt]

Anuj Phogat <anuj.phogat at gmail.com> writes:

> V2:
>    - Update comments.
>    - Make changes to support simd16 mode.
>    - Add compute_pos_offset variable in brw_wm_prog_key.
>    - Add variable uses_omask in brw_wm_prog_data.
>
> Signed-off-by: Anuj Phogat <anuj.phogat at gmail.com>

> +fs_reg *
> +fs_visitor::emit_samplepos_setup(ir_variable *ir)
> +{
> +   assert(brw->gen >= 6);
> +   assert(ir->type == glsl_type::vec2_type);
> +
> +   this->current_annotation = "compute sample position";
> +   fs_reg *reg = new(this->mem_ctx) fs_reg(this, ir->type);
> +   fs_reg pos = *reg;
> +   fs_reg int_sample_x = fs_reg(this, glsl_type::int_type);
> +   fs_reg int_sample_y = fs_reg(this, glsl_type::int_type);
> +
> +   /* WM will be run in MSDISPMODE_PERSAMPLE. So, only one of SIMD8 or SIMD16
> +    * mode will be enabled.
> +    *
> +    * From the Ivy Bridge PRM, volume 2 part 1, page 344:
> +    * R31.1:0         Position Offset X/Y for Slot[3:0]
> +    * R31.3:2         Position Offset X/Y for Slot[7:4]
> +    * .....
> +    *
> +    * The X, Y sample positions come in as bytes in  thread payload. So, read
> +    * the positions using vstride=16, width=8, hstride=2.
> +    */
> +   struct brw_reg sample_pos_reg =
> +      stride(retype(brw_vec1_grf(c->sample_pos_reg, 0),
> +                    BRW_REGISTER_TYPE_B), 16, 8, 2);
> +
> +   emit(MOV(int_sample_x, fs_reg(sample_pos_reg)));
> +   /* Compute gl_SamplePosition.x */
> +   compute_sample_position(pos, int_sample_x);
> +   pos.reg_offset += dispatch_width / 8;

I noticed this during a brief glance at the series: You're incrementing
pos's reg_offset by 2 in the dispatch_width == 16 case, but afaik
ir->type is just a vec2.  If you want to access the second half of a
vec2 GRF, that's just pos.reg_offset++ regardless of whether you're in 8
or 16 mode.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 835 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20131029/f13689b0/attachment.pgp>