From dfd8b92a5b33fbe58240e43d2c0b252db09d9151 Mon Sep 17 00:00:00 2001
From: Dipshet <264011288+Dipshet@users.noreply.github.com>
Date: Wed, 15 Jul 2026 02:03:35 +0200
Subject: [PATCH] D3D12: Fix CONSTANT_ALPHA blend factors collapsing onto
 constant RGB

The D3D12 PipelineBlendFactor enum had no constant-alpha entry, so the Xenos
CONSTANT_ALPHA and ONE_MINUS_CONSTANT_ALPHA blend factors (14, 15) were mapped
onto the constant-COLOR kBlendFactor / kInvBlendFactor - i.e. D3D12 BLEND_FACTOR
/ INV_BLEND_FACTOR, which use the blend constant's RGB rather than its alpha.

Aircraft ground shadow blends with dst = ONE_MINUS_CONSTANT_ALPHA and aSTANT_ALPHA blend factors collapsing onto
blend constant of (0.03, 0.04, 0.04, 0.30): it wants 1 - 0.30 = 0.70 (scale the
background down -> darken), but got 1 - (0.03,0.04,0.04) ~= 0.97 (barely scaled)
with the white source added on top, so the shadow BRIGHTENED instead of
darkening - the "white shadow" bug. Vulkan has the distinct
ONE_MINUS_CONSTANT_ALPHA factor and renders it correctly.

Add kBlendFactorAlpha / kInvBlendFactorAlpha to the enum, route factors 14/15 to
them in both the colour and alpha maps, and map them to D3D12 ALPHA_FACTOR /
INV_ALPHA_FACTOR. Verified fixed on both the RTV and ROV render-target paths.
---
 .../rex/graphics/d3d12/pipeline_cache.h       |  8 ++++++-
 .../src/graphics/d3d12/pipeline_cache.cpp     | 21 ++++++++++++-------
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/thirdparty/rexglue-sdk/include/rex/graphics/d3d12/pipeline_cache.h b/thirdparty/rexglue-sdk/include/rex/graphics/d3d12/pipeline_cache.h
index 7a9d6a29..b56c4bac 100644
--- a/thirdparty/rexglue-sdk/include/rex/graphics/d3d12/pipeline_cache.h
+++ b/thirdparty/rexglue-sdk/include/rex/graphics/d3d12/pipeline_cache.h
@@ -165,6 +165,12 @@ class PipelineCache {
     kBlendFactor,
     kInvBlendFactor,
     kSrcAlphaSat,
+    // Constant blend factor using the constant's ALPHA broadcast to RGB (D3D12
+    // ALPHA_FACTOR / INV_ALPHA_FACTOR). Distinct from kBlendFactor, which uses
+    // the constant's RGB - the Xenos CONSTANT_ALPHA / ONE_MINUS_CONSTANT_ALPHA
+    // factors map here, not onto the RGB ones.
+    kBlendFactorAlpha,
+    kInvBlendFactorAlpha,
   };
 
   // Update PipelineDescription::kVersion if anything is changed!
@@ -219,7 +225,7 @@ class PipelineCache {
 
     PipelineRenderTarget render_targets[xenos::kMaxColorRenderTargets];
 
-    static constexpr uint32_t kVersion = 0x20210425;
+    static constexpr uint32_t kVersion = 0x20260715;
   });
 
   REXPACKEDSTRUCT(PipelineStoredDescription, {
diff --git a/thirdparty/rexglue-sdk/src/graphics/d3d12/pipeline_cache.cpp b/thirdparty/rexglue-sdk/src/graphics/d3d12/pipeline_cache.cpp
index 3dfb0dcc..4d821996 100644
--- a/thirdparty/rexglue-sdk/src/graphics/d3d12/pipeline_cache.cpp
+++ b/thirdparty/rexglue-sdk/src/graphics/d3d12/pipeline_cache.cpp
@@ -1509,10 +1509,10 @@ bool PipelineCache::GetCurrentStateDescription(
         /* 12 */ PipelineBlendFactor::kBlendFactor,
         // ONE_MINUS_CONSTANT_COLOR
         /* 13 */ PipelineBlendFactor::kInvBlendFactor,
-        // CONSTANT_ALPHA
-        /* 14 */ PipelineBlendFactor::kBlendFactor,
-        // ONE_MINUS_CONSTANT_ALPHA
-        /* 15 */ PipelineBlendFactor::kInvBlendFactor,
+        // CONSTANT_ALPHA - uses the constant's ALPHA, not RGB.
+        /* 14 */ PipelineBlendFactor::kBlendFactorAlpha,
+        // ONE_MINUS_CONSTANT_ALPHA - uses 1 - constant ALPHA, not 1 - RGB.
+        /* 15 */ PipelineBlendFactor::kInvBlendFactorAlpha,
         /* 16 */ PipelineBlendFactor::kSrcAlphaSat,
     };
     // Like kBlendFactorMap, but with color modes changed to alpha. Some
@@ -1534,10 +1534,10 @@ bool PipelineCache::GetCurrentStateDescription(
         /* 12 */ PipelineBlendFactor::kBlendFactor,
         // ONE_MINUS_CONSTANT_COLOR
         /* 13 */ PipelineBlendFactor::kInvBlendFactor,
-        // CONSTANT_ALPHA
-        /* 14 */ PipelineBlendFactor::kBlendFactor,
-        // ONE_MINUS_CONSTANT_ALPHA
-        /* 15 */ PipelineBlendFactor::kInvBlendFactor,
+        // CONSTANT_ALPHA - uses the constant's ALPHA, not RGB.
+        /* 14 */ PipelineBlendFactor::kBlendFactorAlpha,
+        // ONE_MINUS_CONSTANT_ALPHA - uses 1 - constant ALPHA, not 1 - RGB.
+        /* 15 */ PipelineBlendFactor::kInvBlendFactorAlpha,
         /* 16 */ PipelineBlendFactor::kSrcAlphaSat,
     };
     // While it's okay to specify fewer render targets in the pipeline state
@@ -2981,6 +2981,11 @@ ID3D12PipelineState* PipelineCache::CreateD3D12Pipeline(
         D3D12_BLEND_DEST_ALPHA,    D3D12_BLEND_INV_DEST_ALPHA,
         D3D12_BLEND_BLEND_FACTOR,  D3D12_BLEND_INV_BLEND_FACTOR,
         D3D12_BLEND_SRC_ALPHA_SAT,
+        // kBlendFactorAlpha / kInvBlendFactorAlpha - the constant's alpha
+        // broadcast to RGB, for the Xenos CONSTANT_ALPHA / ONE_MINUS_CONSTANT_ALPHA
+        // factors (previously collapsed onto the RGB BLEND_FACTOR, which darkened
+        // shadows the wrong way - they brightened instead of subtracting).
+        D3D12_BLEND_ALPHA_FACTOR,  D3D12_BLEND_INV_ALPHA_FACTOR,
     };
     // 8 entries for safety since 3 bits from the guest are passed directly.
     static const D3D12_BLEND_OP kBlendOpMap[] = {