nir/lower_wpos_center: support adding sample position to fragment coordinate
According to section 14.6 of the Vulkan specification: "When sample shading is enabled, the x and y components of FragCoord reflect the location of the sample corresponding to the shader invocation." So add a boolean parameter to the lowering pass to select this behavior when we need it. Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
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@ -2518,7 +2518,7 @@ typedef struct nir_lower_wpos_ytransform_options {
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bool nir_lower_wpos_ytransform(nir_shader *shader,
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const nir_lower_wpos_ytransform_options *options);
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bool nir_lower_wpos_center(nir_shader *shader);
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bool nir_lower_wpos_center(nir_shader *shader, const bool for_sample_shading);
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typedef struct nir_lower_drawpixels_options {
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int texcoord_state_tokens[5];
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@ -39,11 +39,14 @@
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* hardware which provides an integer pixel center. Vulkan mandates that
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* the pixel center must be half-integer, and also that the coordinate
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* system's origin must be upper left. This means that there's no need
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* for a uniform - we can always just add a constant.
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* for a uniform - we can always just add a constant. In the case that
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* sample shading is enabled, Vulkan expects FragCoord to include sample
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* positions.
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*/
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static void
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add_half_to_fragcoord(nir_builder *b, nir_intrinsic_instr *intr)
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update_fragcoord(nir_builder *b, nir_intrinsic_instr *intr,
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const bool for_sample_shading)
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{
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nir_ssa_def *wpos = &intr->dest.ssa;
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@ -51,14 +54,27 @@ add_half_to_fragcoord(nir_builder *b, nir_intrinsic_instr *intr)
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b->cursor = nir_after_instr(&intr->instr);
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if (!for_sample_shading) {
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wpos = nir_fadd(b, wpos, nir_imm_vec4(b, 0.5f, 0.5f, 0.0f, 0.0f));
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} else {
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nir_ssa_def *spos =
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nir_load_system_value(b, nir_intrinsic_load_sample_pos, 0);
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wpos = nir_fadd(b, wpos,
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nir_vec4(b,
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nir_channel(b, spos, 0),
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nir_channel(b, spos, 1),
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nir_imm_float(b, 0.0f),
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nir_imm_float(b, 0.0f)));
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}
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nir_ssa_def_rewrite_uses_after(&intr->dest.ssa, nir_src_for_ssa(wpos),
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wpos->parent_instr);
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}
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static bool
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lower_wpos_center_block(nir_builder *b, nir_block *block)
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lower_wpos_center_block(nir_builder *b, nir_block *block,
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const bool for_sample_shading)
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{
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bool progress = false;
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@ -73,7 +89,7 @@ lower_wpos_center_block(nir_builder *b, nir_block *block)
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var->data.location == VARYING_SLOT_POS) {
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/* gl_FragCoord should not have array/struct derefs: */
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assert(dvar->deref.child == NULL);
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add_half_to_fragcoord(b, intr);
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update_fragcoord(b, intr, for_sample_shading);
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progress = true;
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}
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}
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@ -84,7 +100,7 @@ lower_wpos_center_block(nir_builder *b, nir_block *block)
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}
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bool
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nir_lower_wpos_center(nir_shader *shader)
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nir_lower_wpos_center(nir_shader *shader, const bool for_sample_shading)
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{
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bool progress = false;
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nir_builder b;
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@ -96,7 +112,8 @@ nir_lower_wpos_center(nir_shader *shader)
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nir_builder_init(&b, function->impl);
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nir_foreach_block(block, function->impl) {
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progress = lower_wpos_center_block(&b, block) || progress;
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progress = lower_wpos_center_block(&b, block, for_sample_shading) ||
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progress;
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}
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nir_metadata_preserve(function->impl, nir_metadata_block_index |
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nir_metadata_dominance);
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@ -158,7 +158,7 @@ anv_shader_compile_to_nir(struct anv_device *device,
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nir_var_shader_in | nir_var_shader_out | nir_var_system_value);
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if (stage == MESA_SHADER_FRAGMENT)
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NIR_PASS_V(nir, nir_lower_wpos_center);
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NIR_PASS_V(nir, nir_lower_wpos_center, false);
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/* Now that we've deleted all but the main function, we can go ahead and
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* lower the rest of the constant initializers.
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