[Vulkan] Remove UB-based independent blend logic

On Vulkan, unlike Direct3D, not writing to a color target in the fragment shader produces an undefined result.

src/xenia/gpu/spirv_shader_translator.cc

@@ -1270,19 +1270,16 @@ void SpirvShaderTranslator::StartFragmentShaderBeforeMain() {
       "xe_out_fragment_data_2",
       "xe_out_fragment_data_3",
   };
-  uint32_t fragment_data_outputs_written =
+  uint32_t color_targets_remaining = current_shader().writes_color_targets();
-      current_shader().writes_color_targets() &
+  uint32_t color_target_index;
-      ~GetSpirvShaderModification().pixel.color_outputs_disabled;
+  while (xe::bit_scan_forward(color_targets_remaining, &color_target_index)) {
-  for (uint32_t i = 0; i < xenos::kMaxColorRenderTargets; ++i) {
+    color_targets_remaining &= ~(UINT32_C(1) << color_target_index);
-    if (!(fragment_data_outputs_written & (uint32_t(1) << i))) {
+    spv::Id output_fragment_data_rt = builder_->createVariable(
-      continue;
+        spv::NoPrecision, spv::StorageClassOutput, type_float4_,
-    }
+        kFragmentDataNames[color_target_index]);
-    spv::Id output_fragment_data_rt =
+    output_fragment_data_[color_target_index] = output_fragment_data_rt;
-        builder_->createVariable(spv::NoPrecision, spv::StorageClassOutput,
-                                 type_float4_, kFragmentDataNames[i]);
-    output_fragment_data_[i] = output_fragment_data_rt;
     builder_->addDecoration(output_fragment_data_rt, spv::DecorationLocation,
-                            int(i));
+                            int(color_target_index));
     // Make invariant as pixel shaders may be used for various precise
     // computations.
     builder_->addDecoration(output_fragment_data_rt, spv::DecorationInvariant);

src/xenia/gpu/spirv_shader_translator.h

@@ -46,11 +46,6 @@ class SpirvShaderTranslator : public ShaderTranslator {
     struct PixelShaderModification {
       // Dynamically indexable register count from SQ_PROGRAM_CNTL.
       uint32_t dynamic_addressable_register_count : 8;
-      // Color outputs removed from the shader to implement a zero color write
-      // mask when independent blending (and thus independent write masks) is
-      // not supported without switching to a render pass with some attachments
-      // actually excluded.
-      uint32_t color_outputs_disabled : 4;
     } pixel;
     uint64_t value = 0;
 

src/xenia/gpu/vulkan/vulkan_pipeline_cache.cc

@@ -141,33 +141,6 @@ VulkanPipelineCache::GetCurrentPixelShaderModification(
           shader.GetDynamicAddressableRegisterCount(
               sq_program_cntl.ps_num_reg)));
 
-  const ui::vulkan::VulkanProvider& provider =
-      command_processor_.GetVulkanProvider();
-  const VkPhysicalDeviceFeatures& device_features = provider.device_features();
-  if (!device_features.independentBlend) {
-    // Since without independent blending, the write mask is common for all
-    // attachments, but the render pass may still include the attachments from
-    // previous draws (to prevent excessive render pass changes potentially
-    // doing stores and loads), disable writing to render targets with a
-    // completely empty write mask by removing the output from the shader.
-    // Only explicitly excluding render targets that the shader actually writes
-    // to, for better pipeline storage compatibility between devices with and
-    // without independent blending (so in the usual situation - the shader
-    // doesn't write to any render targets disabled via the color mask - no
-    // explicit disabling of shader outputs will be needed, and the disabled
-    // output mask will be 0).
-    uint32_t color_targets_remaining = shader.writes_color_targets();
-    uint32_t color_target_index;
-    while (xe::bit_scan_forward(color_targets_remaining, &color_target_index)) {
-      color_targets_remaining &= ~(uint32_t(1) << color_target_index);
-      if (!(normalized_color_mask &
-            (uint32_t(0b1111) << (4 * color_target_index)))) {
-        modification.pixel.color_outputs_disabled |= uint32_t(1)
-                                                     << color_target_index;
-      }
-    }
-  }
-
   return modification;
 }