[Mesa-dev] [RFC PATCH 06/10] i965/Gen4-5: Set clip flags from clip distances

[Paul Berry]

On 3 August 2013 19:59, Chris Forbes <chrisf at ijw.co.nz> wrote:

> Signed-off-by: Chris Forbes <chrisf at ijw.co.nz>
> ---
>  src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 25
> ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> index f80777b..c0b5ccd 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
> @@ -2625,7 +2625,6 @@ vec4_visitor::emit_psiz_and_flags(struct brw_reg reg)
>        dst_reg header1 = dst_reg(this, glsl_type::uvec4_type);
>        dst_reg header1_w = header1;
>        header1_w.writemask = WRITEMASK_W;
> -      GLuint i;
>
>        emit(MOV(header1, 0u));
>
> @@ -2637,18 +2636,22 @@ vec4_visitor::emit_psiz_and_flags(struct brw_reg
> reg)
>          emit(AND(header1_w, src_reg(header1_w), 0x7ff << 8));
>        }
>
> -      current_annotation = "Clipping flags";
> -      for (i = 0; i < key->nr_userclip_plane_consts; i++) {
> -        vec4_instruction *inst;
> -         gl_varying_slot slot = (prog_data->vue_map.slots_valid &
> VARYING_BIT_CLIP_VERTEX)
> -            ? VARYING_SLOT_CLIP_VERTEX : VARYING_SLOT_POS;
> +      if (key->userclip_active) {
> +         current_annotation = "Clipping flags";
> +         dst_reg temp = dst_reg(this, glsl_type::uint_type);
> +         dst_reg temp2 = dst_reg(this, glsl_type::uint_type);
>
> -        inst = emit(DP4(dst_null_f(), src_reg(output_reg[slot]),
> -                         src_reg(this->userplane[i])));
> -        inst->conditional_mod = BRW_CONDITIONAL_L;
> +         emit(CMP(temp, src_reg(output_reg[VARYING_SLOT_CLIP_DIST0]),
> src_reg(0.0f), BRW_CONDITIONAL_L));
> +         emit(AND(temp2, src_reg(temp), src_reg(0x0fu)));
>

I don't think this works.  From the i965 PRM (
https://01.org/linuxgraphics/sites/default/files/documentation/965_g35_vol_4_subsystem_core_1.pdf),
page 425:

"Destination operand can be a GRF, an MRF or a null register. If it is not
null, for the enabled channels, the LSB of the result in the destination
channel contains the flag value for the channel. The other bits are
undefined."

You're making use of the lower 4 bits of the result, 3 of which are
undefined.

I believe you can achieve the effect you want by reading from the "flag"
register, though you'll have to do some bit swizzling to unpack the values
you want, since the flag register stores the result of the comparison for
vertex 0 in its lower nibble and the result of the comparison for vertex 1
in its lower nibble.


>
> -        inst = emit(OR(header1_w, src_reg(header1_w), 1u << i));
> -        inst->predicate = BRW_PREDICATE_NORMAL;
> +         emit(CMP(temp, src_reg(output_reg[VARYING_SLOT_CLIP_DIST1]),
> src_reg(0.0f), BRW_CONDITIONAL_L));
> +         emit(AND(temp, src_reg(temp), src_reg(0x0fu)));
> +         emit(SHL(temp, src_reg(temp), src_reg(4)));
> +         emit(OR(temp2, src_reg(temp2), src_reg(temp)));
> +
> +         /* mask just the enabled planes */
> +         emit(AND(temp2, src_reg(temp2),
> src_reg(ctx->Transform.ClipPlanesEnabled)));
> +         emit(OR(header1_w, src_reg(header1_w), src_reg(temp2)));
>        }
>
>        /* i965 clipping workaround:
> --
> 1.8.3.4
>
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