From 6b28e6870e5a0b0c3e630264915b367d1d4a6f8a Mon Sep 17 00:00:00 2001
From: Evan Hemsley <2342303+thatcosmonaut@users.noreply.github.com>
Date: Tue, 5 May 2026 12:55:16 -0700
Subject: [PATCH] GPU: D3D12 stencil plane transition (#15519)

(cherry picked from commit fee8c94b5c7211dd04349470a6ff333f07ac0d99)
---
 src/gpu/d3d12/SDL_gpu_d3d12.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/gpu/d3d12/SDL_gpu_d3d12.c b/src/gpu/d3d12/SDL_gpu_d3d12.c
index 21050f39f1..b5a6e50f1e 100644
--- a/src/gpu/d3d12/SDL_gpu_d3d12.c
+++ b/src/gpu/d3d12/SDL_gpu_d3d12.c
@@ -1792,6 +1792,16 @@ static inline Uint32 D3D12_INTERNAL_CalcSubresource(
     return mipLevel + (layer * numLevels);
 }
 
+static inline Uint32 D3D12_INTERNAL_CalcSubresourceWithPlane(
+    Uint32 mipLevel,
+    Uint32 layer,
+    Uint32 planeSlice,
+    Uint32 numLevels,
+    Uint32 arraySize)
+{
+    return mipLevel + (layer * numLevels) + (planeSlice * numLevels * arraySize);
+}
+
 static void D3D12_INTERNAL_ResourceBarrier(
     D3D12CommandBuffer *commandBuffer,
     D3D12_RESOURCE_STATES sourceState,
@@ -1848,6 +1858,27 @@ static void D3D12_INTERNAL_TextureSubresourceBarrier(
         textureSubresource->parent->resource,
         textureSubresource->index,
         needsUAVBarrier);
+
+    // D3D12 stores planar values on a separate subresource.
+    // Since depth-stencil is our only supported planar format,
+    // just force an extra transition if we're using a stencil format.
+    if (IsStencilFormat(textureSubresource->parent->container->header.info.format)) {
+        Uint32 planeSubresourceIndex = D3D12_INTERNAL_CalcSubresourceWithPlane(
+            textureSubresource->level,
+            textureSubresource->layer,
+            1,
+            textureSubresource->parent->container->header.info.num_levels,
+            textureSubresource->parent->container->header.info.layer_count_or_depth
+        );
+
+        D3D12_INTERNAL_ResourceBarrier(
+            commandBuffer,
+            sourceState,
+            destinationState,
+            textureSubresource->parent->resource,
+            planeSubresourceIndex,
+            needsUAVBarrier);
+    }
 }
 
 static D3D12_RESOURCE_STATES D3D12_INTERNAL_DefaultTextureResourceState(