Implement native composite source handling for Mario Kart Wii ghost kart effect

OPENXR.md

@@ -750,7 +750,21 @@ full-screen orthographic quad then darkens the image by destination alpha. The e
 volumes, so that alpha exists in each eye, and the quad has to cover the whole eye: on the virtual
 screen it shaded only the screen's rectangle, cutting every shadow off at its edge. Retained one-shot
 EFB bakes such as Mario Kart Wii's minimap are treated as game art and remain eligible for the
-screen. A reprojected 2D draw
+screen.
+
+One native effect is replayed differently: a composite that samples a freshly produced,
+frame-sized depth copy. Mario Kart Wii draws a ghost kart by rendering it alone into the cleared
+EFB, copying the frame's colour and depth out, drawing the race, and blending the copies back
+with one orthographic quad whose depth comes from the depth copy. Left on its recorded transforms,
+that quad stamps the desktop's flat image of the ghost over each eye, following the head and cut
+off by the eye's own ground. An eye therefore skips the perspective draws of the pass that
+produced the depth copy where they were recorded and re-issues them in the composite's place,
+with this eye's transforms, a constant-alpha blend (`kCompositeSourceAlpha`, about the strength of
+the game's own composite) and a depth test against the world the eye has drawn by then: the ghost
+in stereo, translucent, where the game put it. The desktop image is unchanged. The link is logged
+once (`Immersive replay: pass N ... is re-issued by each eye`).
+
+A reprojected 2D draw
 uses the full eye viewport and scissor because its recorded rectangle no longer describes where it
 ended up; its original viewport is folded into the projection instead.
 

aurora-main/lib/gfx/common.cpp

@@ -208,6 +208,9 @@ struct RenderPass {
   bool postCopyClear = false;
   bool snapshotColorResolveSource = false;
   bool efbTarget = false;
+  // This pass's perspective draws are re-issued by an eye at the composite that samples its
+  // depth copy (link_composite_sources), and skipped where they were recorded.
+  bool compositeSource = false;
   std::vector<tex_palette_conv::ConvRequest> paletteConvs;
 };
 static std::vector<RenderPass> g_renderPasses;
@@ -1647,6 +1650,66 @@ static bool prepare_stereo_replay_uniforms(const StereoReplayFrame& stereoFrame,
   return true;
 }
 
+// Mario Kart Wii draws a ghost kart by rendering it alone into the cleared EFB, copying the
+// frame's colour and depth out, drawing the race, and blending the copies back with one
+// orthographic quad whose depth comes from the depth copy. That quad is a native effect, so an
+// eye would stamp the desktop's flat image of the ghost over its own view, following the head
+// and cut by the eye's ground. Instead the eye skips the draws of the pass that produced the
+// depth copy where they were recorded and re-issues them in the composite's place, blended
+// with kCompositeSourceAlpha and depth-tested against the eye's own world: the ghost in stereo,
+// translucent, where the game put it. Runs once the frame's passes are complete, on the
+// producer, before the frame is sealed.
+static void link_composite_sources() noexcept {
+  if (g_stereoLocalPlayerCount > 1) {
+    return;
+  }
+  static bool linkLogged = false;
+  for (size_t i = 0; i < g_renderPasses.size(); ++i) {
+    if (!g_renderPasses[i].efbTarget) {
+      continue;
+    }
+    for (auto& command : g_renderPasses[i].commands) {
+      if (command.type != CommandType::Draw || command.data.draw.type != ShaderType::GX) {
+        continue;
+      }
+      auto& layout = command.data.draw.gx.uniformReplayLayout;
+      layout.compositeSourcePass = -1;
+      if (!layout.nativeEfbEffect || layout.perspective || layout.compositeDepthCopy == nullptr) {
+        continue;
+      }
+      for (size_t p = i; p-- > 0;) {
+        auto& source = g_renderPasses[p];
+        if (!source.efbTarget || source.resolveTarget.get() != layout.compositeDepthCopy) {
+          continue;
+        }
+        size_t draws = 0;
+        for (auto& sourceCommand : source.commands) {
+          if (sourceCommand.type != CommandType::Draw || sourceCommand.data.draw.type != ShaderType::GX) {
+            continue;
+          }
+          auto& sourceDraw = sourceCommand.data.draw.gx;
+          if (sourceDraw.uniformReplayLayout.perspective &&
+              gx::resolve_composite_source_pipelines(sourceDraw.configHash, sourceDraw.stereoGhostPipeline,
+                                                     sourceDraw.stereoGhostStencilPipeline)) {
+            ++draws;
+          }
+        }
+        if (draws > 0) {
+          source.compositeSource = true;
+          layout.compositeSourcePass = static_cast<int32_t>(p);
+          if (!linkLogged) {
+            linkLogged = true;
+            Log.info("Immersive replay: pass {} ({} perspective draws) is re-issued by each eye in place of the "
+                     "composite in pass {} that samples its depth copy",
+                     p, draws, i);
+          }
+        }
+        break;
+      }
+    }
+  }
+}
+
 static bool end_batch_impl(const wgpu::CommandEncoder& cmd, bool advanceFrame,
                            const StereoReplayFrame* stereoFrame = nullptr) {
   ZoneScoped;
@@ -1666,6 +1729,9 @@ static bool end_batch_impl(const wgpu::CommandEncoder& cmd, bool advanceFrame,
   const bool stereoPrepared = (stereoFrame == nullptr && !captureStereo) ||
                               prepare_stereo_replay_uniforms(stereoFrame != nullptr ? *stereoFrame : placeholder,
                                                              captureStereo ? &g_pendingLateStereo : nullptr);
+  if (stereoPrepared && (stereoFrame != nullptr || captureStereo)) {
+    link_composite_sources();
+  }
   if (captureStereo && stereoPrepared) {
     g_pendingLateStereo.generation = g_replayBufferGeneration.load(std::memory_order_acquire);
   } else {
@@ -2581,6 +2647,102 @@ static void render_pass_impl(const wgpu::RenderPassEncoder& pass, const std::vec
                      recordedViewport.znear, recordedViewport.zfar);
   };
 
+  // WebGPU requires 0 <= minDepth <= maxDepth <= 1. vp.znear/vp.zfar are in GX's own distance
+  // terms (0 = near); under UseReversedZ the host depth-buffer storage direction is flipped
+  // (near = 1, far = 0), so this range has to be remapped through 1-x the same way the
+  // projection matrix, depth compare function, and clear value all are - a plain min/max clamp
+  // (the previous code here) maps a *restricted* range (e.g. a viewport deliberately narrowed
+  // to force something to draw "in front of everything") to the wrong end of the buffer: what
+  // should land near the near-storage-extreme (1.0) instead lands near the far-storage-extreme
+  // (0.0), so anything else drawn afterward at its true depth wins the compare test and the
+  // "in front" geometry silently vanishes. A full [0,1] viewport is unaffected either way,
+  // which is why this only broke specific elements, not the whole scene. Matches upstream
+  // aurora's apply_viewport (lib/gfx/encoding.cpp).
+  //
+  // The remapped pair is then ordered and clamped before it reaches WebGPU. For any ordered
+  // guest range this is a no-op (znear <= zfar implies 1-zfar <= 1-znear), so upstream's fix is
+  // reproduced exactly; it only guards the swapped pair MKW is known to emit, which the raw
+  // remap would hand to SetViewport as minDepth > maxDepth and fail validation. The VR eye
+  // replay below reuses these recorded values, so the guard covers that path too.
+  const auto map_viewport = [&](const Viewport& vp) noexcept {
+    const float remappedNear = gx::UseReversedZ ? 1.0f - vp.zfar : vp.znear;
+    const float remappedFar = gx::UseReversedZ ? 1.0f - vp.znear : vp.zfar;
+    const float minDepth = std::clamp(std::min(remappedNear, remappedFar), 0.0f, 1.0f);
+    const float maxDepth = std::clamp(std::max(remappedNear, remappedFar), 0.0f, 1.0f);
+    return Viewport{
+        .left = (vp.left - static_cast<float>(sourceRegionLeft)) * scaleX,
+        .top = (vp.top - static_cast<float>(sourceRegionTop)) * scaleY,
+        .width = vp.width * scaleX,
+        .height = vp.height * scaleY,
+        .znear = minDepth,
+        .zfar = maxDepth,
+    };
+  };
+  const auto map_scissor = [&](const ClipRect& sc) noexcept {
+    const auto sourceLeft = std::clamp(sc.x, sourceRegionLeft, sourceRegionRight);
+    const auto sourceTop = std::clamp(sc.y, sourceRegionTop, sourceRegionBottom);
+    const auto sourceRight = std::clamp(sc.x + sc.width, sourceLeft, sourceRegionRight);
+    const auto sourceBottom = std::clamp(sc.y + sc.height, sourceTop, sourceRegionBottom);
+    const auto left = static_cast<uint32_t>(
+        std::clamp(static_cast<int32_t>(std::floor(static_cast<float>(sourceLeft - sourceRegionLeft) * scaleX)), 0,
+                   static_cast<int32_t>(targetSize.width)));
+    const auto top = static_cast<uint32_t>(
+        std::clamp(static_cast<int32_t>(std::floor(static_cast<float>(sourceTop - sourceRegionTop) * scaleY)), 0,
+                   static_cast<int32_t>(targetSize.height)));
+    const auto right = static_cast<uint32_t>(
+        std::clamp(static_cast<int32_t>(std::ceil(static_cast<float>(sourceRight - sourceRegionLeft) * scaleX)),
+                   static_cast<int32_t>(left), static_cast<int32_t>(targetSize.width)));
+    const auto bottom = static_cast<uint32_t>(
+        std::clamp(static_cast<int32_t>(std::ceil(static_cast<float>(sourceBottom - sourceRegionTop) * scaleY)),
+                   static_cast<int32_t>(top), static_cast<int32_t>(targetSize.height)));
+    return std::array<uint32_t, 4>{left, top, right - left, bottom - top};
+  };
+  // The perspective draws of a composite's source pass, in the composite's place: their own
+  // recorded viewport and scissor, this eye's uniforms, the constant-alpha pipeline sibling,
+  // depth-tested against the world the eye has drawn by now (see link_composite_sources).
+  const auto replay_composite_source = [&](const RenderPass& source) {
+    const wgpu::Color alpha{stereo_replay::kCompositeSourceAlpha, stereo_replay::kCompositeSourceAlpha,
+                            stereo_replay::kCompositeSourceAlpha, stereo_replay::kCompositeSourceAlpha};
+    const bool stencilTarget = invocation.target->depthFormat == wgpu::TextureFormat::Depth24PlusStencil8;
+    for (const auto& command : source.commands) {
+      if (command.type == CommandType::SetViewport) {
+        const Viewport vp = map_viewport(command.data.setViewport);
+        pass.SetViewport(vp.left, vp.top, vp.width, vp.height, vp.znear, vp.zfar);
+        continue;
+      }
+      if (command.type == CommandType::SetScissor) {
+        apply_scissor(map_scissor(command.data.setScissor));
+        continue;
+      }
+      if (command.type != CommandType::Draw || command.data.draw.type != ShaderType::GX) {
+        continue;
+      }
+      const auto& draw = command.data.draw.gx;
+      if (!draw.uniformReplayLayout.perspective) {
+        continue;
+      }
+      const gfx::PipelineRef pipeline = stencilTarget ? draw.stereoGhostStencilPipeline : draw.stereoGhostPipeline;
+      if (pipeline == 0) {
+        continue;
+      }
+      const gfx::Range* uniform = nullptr;
+      if (invocation.stereoEye < draw.stereoUniformRanges.size() &&
+          draw.stereoUniformRanges[invocation.stereoEye].size != 0) {
+        uniform = &draw.stereoUniformRanges[invocation.stereoEye];
+      } else if (invocation.interpolatedFrame >= 0 &&
+                 static_cast<size_t>(invocation.interpolatedFrame) < draw.interpolatedUniformRanges.size() &&
+                 draw.interpolatedUniformRanges[invocation.interpolatedFrame].size != 0) {
+        uniform = &draw.interpolatedUniformRanges[invocation.interpolatedFrame];
+      }
+      gx::render(draw, pass, encodeState, source.requireReadyPipelines, uniform, pipeline, &alpha);
+    }
+    if (invocation.sceneDrawn != nullptr) {
+      *invocation.sceneDrawn = true;
+    }
+    // The source pass's own viewport and scissor were applied; the next draw restores its own.
+    viewportStateKnown = false;
+    scissorStateKnown = false;
+  };
   for (const auto& cmd : renderPasses[idx].commands) {
 #ifdef AURORA_GFX_DEBUG_GROUPS
     {
@@ -2604,35 +2766,7 @@ static void render_pass_impl(const wgpu::RenderPassEncoder& pass, const std::vec
     case CommandType::SetViewport: {
       const auto& vp = cmd.data.setViewport;
       sourceViewport = {vp.left, vp.top, vp.width, vp.height};
-      // WebGPU requires 0 <= minDepth <= maxDepth <= 1. vp.znear/vp.zfar are in GX's own distance
-      // terms (0 = near); under UseReversedZ the host depth-buffer storage direction is flipped
-      // (near = 1, far = 0), so this range has to be remapped through 1-x the same way the
-      // projection matrix, depth compare function, and clear value all are - a plain min/max clamp
-      // (the previous code here) maps a *restricted* range (e.g. a viewport deliberately narrowed
-      // to force something to draw "in front of everything") to the wrong end of the buffer: what
-      // should land near the near-storage-extreme (1.0) instead lands near the far-storage-extreme
-      // (0.0), so anything else drawn afterward at its true depth wins the compare test and the
-      // "in front" geometry silently vanishes. A full [0,1] viewport is unaffected either way,
-      // which is why this only broke specific elements, not the whole scene. Matches upstream
-      // aurora's apply_viewport (lib/gfx/encoding.cpp).
-      //
-      // The remapped pair is then ordered and clamped before it reaches WebGPU. For any ordered
-      // guest range this is a no-op (znear <= zfar implies 1-zfar <= 1-znear), so upstream's fix is
-      // reproduced exactly; it only guards the swapped pair MKW is known to emit, which the raw
-      // remap would hand to SetViewport as minDepth > maxDepth and fail validation. The VR eye
-      // replay below reuses these recorded values, so the guard covers that path too.
-      const float remappedNear = gx::UseReversedZ ? 1.0f - vp.zfar : vp.znear;
-      const float remappedFar = gx::UseReversedZ ? 1.0f - vp.znear : vp.zfar;
-      const float minDepth = std::clamp(std::min(remappedNear, remappedFar), 0.0f, 1.0f);
-      const float maxDepth = std::clamp(std::max(remappedNear, remappedFar), 0.0f, 1.0f);
-      recordedViewport = {
-          .left = (vp.left - static_cast<float>(sourceRegionLeft)) * scaleX,
-          .top = (vp.top - static_cast<float>(sourceRegionTop)) * scaleY,
-          .width = vp.width * scaleX,
-          .height = vp.height * scaleY,
-          .znear = minDepth,
-          .zfar = maxDepth,
-      };
+      recordedViewport = map_viewport(vp);
       hudScreenViewport = false;
       viewportStateKnown = true;
       apply_viewport(false);
@@ -2640,23 +2774,7 @@ static void render_pass_impl(const wgpu::RenderPassEncoder& pass, const std::vec
     case CommandType::SetScissor: {
       const auto& sc = cmd.data.setScissor;
       sourceScissor = {float(sc.x), float(sc.y), float(sc.width), float(sc.height)};
-      const auto sourceLeft = std::clamp(sc.x, sourceRegionLeft, sourceRegionRight);
-      const auto sourceTop = std::clamp(sc.y, sourceRegionTop, sourceRegionBottom);
-      const auto sourceRight = std::clamp(sc.x + sc.width, sourceLeft, sourceRegionRight);
-      const auto sourceBottom = std::clamp(sc.y + sc.height, sourceTop, sourceRegionBottom);
-      const auto left = static_cast<uint32_t>(
-          std::clamp(static_cast<int32_t>(std::floor(static_cast<float>(sourceLeft - sourceRegionLeft) * scaleX)), 0,
-                     static_cast<int32_t>(targetSize.width)));
-      const auto top = static_cast<uint32_t>(
-          std::clamp(static_cast<int32_t>(std::floor(static_cast<float>(sourceTop - sourceRegionTop) * scaleY)), 0,
-                     static_cast<int32_t>(targetSize.height)));
-      const auto right = static_cast<uint32_t>(
-          std::clamp(static_cast<int32_t>(std::ceil(static_cast<float>(sourceRight - sourceRegionLeft) * scaleX)),
-                     static_cast<int32_t>(left), static_cast<int32_t>(targetSize.width)));
-      const auto bottom = static_cast<uint32_t>(
-          std::clamp(static_cast<int32_t>(std::ceil(static_cast<float>(sourceBottom - sourceRegionTop) * scaleY)),
-                     static_cast<int32_t>(top), static_cast<int32_t>(targetSize.height)));
-      recordedScissor = {left, top, right - left, bottom - top};
+      recordedScissor = map_scissor(sc);
       hudScreenScissor = false;
       scissorStateKnown = true;
       apply_scissor(recordedScissor);
@@ -2677,6 +2795,15 @@ static void render_pass_impl(const wgpu::RenderPassEncoder& pass, const std::vec
                             !stereo_replay::subviews_overlap(sourceScissor, playerRegion))) {
           break;
         }
+        // A composite's source pass is drawn at the composite instead (link_composite_sources).
+        if (overrideTarget && renderPasses[idx].compositeSource) {
+          break;
+        }
+        if (overrideTarget && draw.gx.uniformReplayLayout.compositeSourcePass >= 0 &&
+            static_cast<size_t>(draw.gx.uniformReplayLayout.compositeSourcePass) < renderPasses.size()) {
+          replay_composite_source(renderPasses[static_cast<size_t>(draw.gx.uniformReplayLayout.compositeSourcePass)]);
+          break;
+        }
         const gfx::Range* uniformOverride = nullptr;
         // Only a 2D draw the virtual screen actually claimed carries a stereo
         // uniform range without being perspective.

aurora-main/lib/gfx/stereo_replay.hpp

@@ -6,6 +6,11 @@
 
 namespace aurora::gfx::stereo_replay {
 
+// The alpha an eye re-issues a composite's source draws with (Mario Kart Wii's ghost kart).
+// The game's own composite blends its copy of the ghost at about half strength; the constant
+// stands in for the alpha that quad carries in its vertex colour.
+constexpr float kCompositeSourceAlpha = 0.5f;
+
 struct SubviewRect {
   float left = 0.f;
   float top = 0.f;

aurora-main/lib/gx/command_processor.cpp

@@ -2281,10 +2281,48 @@ static const CachedPipelineState& resolve_pipeline_state(GXPrimitive prim, GXVtx
 // Lazily cache eye-format siblings alongside the ordinary pipeline. Steady-state
 // draws only read the refs: no extra config population/hashing on the Quest CPU.
 // Shader modules are shared by the depth-format variants.
+// The configs of the perspective draws recorded while a stereo frame provider is active, so a
+// pass found later to be a composite's source (link_composite_sources) can have constant-alpha
+// siblings built for exactly its draws. Nothing is compiled here; cached_pipeline_state's slot
+// can be overwritten by the time the frame is sealed, which is why the config is kept by value.
+struct CompositeSourceConfig {
+  PipelineConfig config{};
+  gfx::PipelineRef plain = 0;
+  gfx::PipelineRef stencil = 0;
+};
+static absl::flat_hash_map<HashType, CompositeSourceConfig> s_compositeSourceConfigs;
+static std::mutex s_compositeSourceConfigsMutex;
+constexpr size_t kMaxCompositeSourceConfigs = 4096;
+
+static void remember_composite_source_config(const CachedPipelineState& state) {
+  std::lock_guard lock{s_compositeSourceConfigsMutex};
+  if (s_compositeSourceConfigs.contains(state.configHash)) return;
+  if (s_compositeSourceConfigs.size() >= kMaxCompositeSourceConfigs) s_compositeSourceConfigs.clear();
+  s_compositeSourceConfigs.emplace(state.configHash, CompositeSourceConfig{.config = *state.config});
+}
+
+static bool resolve_composite_source_pipelines_impl(HashType configHash, gfx::PipelineRef& plain,
+                                                    gfx::PipelineRef& stencil) {
+  std::lock_guard lock{s_compositeSourceConfigsMutex};
+  const auto it = s_compositeSourceConfigs.find(configHash);
+  if (it == s_compositeSourceConfigs.end()) return false;
+  auto& entry = it->second;
+  if (entry.plain == 0) {
+    PipelineConfig config = entry.config;
+    config.stereoStencil = kCompositeSourceBlend;
+    entry.plain = gfx::pipeline_ref(config);
+    config.stereoStencil = kCompositeSourceBlend | kStereoStencilFormat;
+    entry.stencil = gfx::pipeline_ref(config);
+  }
+  plain = entry.plain;
+  stencil = entry.stencil;
+  return true;
+}
+
 static void resolve_replay_pipelines(const CachedPipelineState& state, bool screen) {
   if (state.stereoRef && (!screen || state.stereoScreenRef)) return;
   PipelineConfig config = *state.config;
-  config.stereoStencil = 1;
+  config.stereoStencil = kStereoStencilFormat;
   if (!state.stereoRef) state.stereoRef = gfx::pipeline_ref(config);
   if (screen && !state.stereoScreenRef) {
     config.shaderConfig.exactScreenDepth = 1;
@@ -2499,6 +2537,7 @@ static void handle_draw_unmerged(GXPrimitive prim, GXVtxFmt fmt, u16 vtxCount, g
   const bool stereo = aurora::stereo_frame_provider_active();
   const bool screen = !replayLayout.perspective && !replayLayout.nativeEfbEffect;
   if (stereo) resolve_replay_pipelines(pipelineState, screen);
+  if (stereo && replayLayout.perspective) remember_composite_source_config(pipelineState);
   s_lastDrawRecordedInterpolation = interpolationIdentityActive;
 
   uint32_t instanceCount = 1;
@@ -2521,6 +2560,7 @@ static void handle_draw_unmerged(GXPrimitive prim, GXVtxFmt fmt, u16 vtxCount, g
       .stereoUniformRanges = {},
       .previousUniformRange = uniformRanges.previous,
       .uniformReplayLayout = uniformRanges.replayLayout,
+      .configHash = pipelineState.configHash,
       .vtxCount = vtxCount,
       .indexCount = numIndices,
       .instanceCount = instanceCount,
@@ -2697,3 +2737,8 @@ bool handle_aurora(const u8* data, u32& pos, u32 size, bool bigEndian) {
 }
 
 } // namespace aurora::gx::fifo
+
+bool aurora::gx::resolve_composite_source_pipelines(HashType configHash, gfx::PipelineRef& plain,
+                                                    gfx::PipelineRef& stencil) {
+  return fifo::resolve_composite_source_pipelines_impl(configHash, plain, stencil);
+}

aurora-main/lib/gx/gx.cpp

@@ -1609,12 +1609,13 @@ static inline wgpu::PrimitiveState to_primitive_state(GXCullMode gx_cullMode) {
 wgpu::RenderPipeline build_pipeline(const PipelineConfig& config, ArrayRef<wgpu::VertexBufferLayout> vtxBuffers,
                                     wgpu::ShaderModule shader, const char* label) noexcept {
   ZoneScoped;
-  const bool maskCockpit = config.stereoStencil && config.shaderConfig.exactScreenDepth;
+  const bool stencilTarget = (config.stereoStencil & kStereoStencilFormat) != 0;
+  const bool maskCockpit = stencilTarget && config.shaderConfig.exactScreenDepth;
   const wgpu::StencilFaceState stencil{
       .compare = maskCockpit ? wgpu::CompareFunction::Equal : wgpu::CompareFunction::Always,
   };
   const wgpu::DepthStencilState depthStencil{
-      .format = config.stereoStencil ? wgpu::TextureFormat::Depth24PlusStencil8 : g_graphicsConfig.depthFormat,
+      .format = stencilTarget ? wgpu::TextureFormat::Depth24PlusStencil8 : g_graphicsConfig.depthFormat,
       .depthWriteEnabled = config.depthUpdate,
       .depthCompare = config.depthCompare ? to_compare_function(config.depthFunc) : wgpu::CompareFunction::Always,
       .stencilFront = stencil,
@@ -1622,8 +1623,22 @@ wgpu::RenderPipeline build_pipeline(const PipelineConfig& config, ArrayRef<wgpu:
       .stencilReadMask = 1,
       .stencilWriteMask = 0,
   };
-  const auto blendState = to_blend_state(config.blendMode, config.blendFacSrc, config.blendFacDst, config.blendOp,
+  auto blendState = to_blend_state(config.blendMode, config.blendFacSrc, config.blendFacDst, config.blendOp,
                                          config.pixelFmt, config.dstAlpha);
+  if ((config.stereoStencil & kCompositeSourceBlend) != 0) {
+    // A composite's source draw re-issued by an eye: opaque geometry laid over the world at
+    // the blend constant's alpha, the alpha the game's own composite quad would have used.
+    blendState.color = wgpu::BlendComponent{
+        .operation = wgpu::BlendOperation::Add,
+        .srcFactor = wgpu::BlendFactor::Constant,
+        .dstFactor = wgpu::BlendFactor::OneMinusConstant,
+    };
+    blendState.alpha = wgpu::BlendComponent{
+        .operation = wgpu::BlendOperation::Add,
+        .srcFactor = wgpu::BlendFactor::One,
+        .dstFactor = wgpu::BlendFactor::Zero,
+    };
+  }
   const std::array colorTargets{wgpu::ColorTargetState{
       .format = g_graphicsConfig.surfaceConfiguration.format,
       .blend = &blendState,

aurora-main/lib/gx/pipeline.cpp

@@ -66,7 +66,8 @@ void clear_shader_module_cache() {
 }
 
 void render(const DrawData& data, const wgpu::RenderPassEncoder& pass, DrawEncodeState& state,
-            bool requireReadyPipeline, const gfx::Range* uniformRangeOverride, gfx::PipelineRef pipelineOverride) {
+            bool requireReadyPipeline, const gfx::Range* uniformRangeOverride, gfx::PipelineRef pipelineOverride,
+            const wgpu::Color* blendConstantOverride) {
   const gfx::PipelineRef pipeline = pipelineOverride != 0 ? pipelineOverride : data.pipeline;
   if (!gfx::bind_pipeline(pipeline, pass, state.currentPipeline, requireReadyPipeline)) {
     return;
@@ -83,7 +84,9 @@ void render(const DrawData& data, const wgpu::RenderPassEncoder& pass, DrawEncod
     wgpuRenderPassEncoderSetBindGroup(pass.Get(), 2, data.bindGroups.resolvedTextureBindGroup, 0, nullptr);
     state.boundTextureBindGroup = data.bindGroups.resolvedTextureBindGroup;
   }
-  if (data.dstAlpha != UINT32_MAX) {
+  if (blendConstantOverride != nullptr) {
+    pass.SetBlendConstant(blendConstantOverride);
+  } else if (data.dstAlpha != UINT32_MAX) {
     const wgpu::Color color{0.f, 0.f, 0.f, data.dstAlpha / 255.f};
     pass.SetBlendConstant(&color);
   }

aurora-main/lib/gx/pipeline.hpp

@@ -14,6 +14,11 @@ struct DrawData {
   // Eye depth/stencil format siblings. Shader modules are shared with mono.
   gfx::PipelineRef stereoPipeline = 0;
   gfx::PipelineRef stereoScreenPipeline = 0;
+  // Constant-alpha siblings, resolved only for the draws of a composite's source pass
+  // (link_composite_sources) from the config remembered under configHash.
+  gfx::PipelineRef stereoGhostPipeline = 0;
+  gfx::PipelineRef stereoGhostStencilPipeline = 0;
+  HashType configHash = 0;
   gfx::Range vertRange;
   gfx::Range idxRange;
   gfx::Range uniformRange;
@@ -34,6 +39,11 @@ struct DrawData {
 
 constexpr uint32_t GXPipelineConfigVersion = 21;
 
+// PipelineConfig::stereoStencil: the eye's Depth24PlusStencil8 target, and the constant-alpha
+// blend an eye uses to re-issue a composite's source draws (see UniformReplayLayout).
+constexpr uint32_t kStereoStencilFormat = 1u;
+constexpr uint32_t kCompositeSourceBlend = 2u;
+
 constexpr GXFogType effective_pipeline_fog_type(GXFogType fogType, GXZTexOp zTextureOp, bool zCompLocBeforeTex,
                                                 GXBlendMode blendMode, GXLogicOp logicOp) noexcept {
   const bool usesLateZTexture = zTextureOp != GX_ZT_DISABLE && !zCompLocBeforeTex;
@@ -44,6 +54,8 @@ constexpr GXFogType effective_pipeline_fog_type(GXFogType fogType, GXZTexOp zTex
 struct PipelineConfig {
   uint32_t version = GXPipelineConfigVersion;
   uint32_t msaaSamples = 1;
+  // Bits of kStereoStencilFormat and kCompositeSourceBlend. One field, so the on-disk
+  // pipeline recipes recorded before the second bit existed stay valid.
   uint32_t stereoStencil = 0;
   ShaderConfig shaderConfig;
   GXCompare depthFunc;
@@ -65,7 +77,7 @@ inline bool valid_pipeline_config(const PipelineConfig& config) noexcept {
   };
   const bool validSamples =
       config.msaaSamples == 1 || config.msaaSamples == 2 || config.msaaSamples == 4 || config.msaaSamples == 8;
-  return config.version == GXPipelineConfigVersion && validSamples && config.stereoStencil <= 1 && in_range(config.depthFunc, GX_ALWAYS) &&
+  return config.version == GXPipelineConfigVersion && validSamples && config.stereoStencil <= (kStereoStencilFormat | kCompositeSourceBlend) && in_range(config.depthFunc, GX_ALWAYS) &&
          in_range(config.cullMode, GX_CULL_ALL) && in_range(config.blendMode, GX_BM_SUBTRACT) &&
          in_range(config.blendFacSrc, GX_BL_INVDSTALPHA) && in_range(config.blendFacDst, GX_BL_INVDSTALPHA) &&
          in_range(config.blendOp, GX_LO_SET) && in_range(config.pixelFmt, GX_PF_YUV420);
@@ -87,7 +99,11 @@ struct DrawEncodeState {
 
 void render(const DrawData& data, const wgpu::RenderPassEncoder& pass, DrawEncodeState& state,
             bool requireReadyPipeline, const gfx::Range* uniformRangeOverride = nullptr,
-            gfx::PipelineRef pipelineOverride = 0);
+            gfx::PipelineRef pipelineOverride = 0, const wgpu::Color* blendConstantOverride = nullptr);
+
+// The constant-alpha (kCompositeSourceBlend) siblings of the pipeline recorded under configHash,
+// for a stencil-less and a stencil eye target. False when the config is no longer remembered.
+bool resolve_composite_source_pipelines(HashType configHash, gfx::PipelineRef& plain, gfx::PipelineRef& stencil);
 
 void queue_surface(const u8* dlStart, uint32_t dlSize, bool bigEndian) noexcept;
 } // namespace aurora::gx

aurora-main/lib/gx/shader_info.cpp

@@ -743,6 +743,7 @@ UniformRanges build_uniform(const ShaderInfo& info, u32 vtxStart, const BindGrou
   // eligible for the virtual screen even when small and alpha blended.
   bool samplesRecentEfbCopy = false;
   bool samplesReducedEfbCopy = false;
+  const gfx::TextureRef* compositeDepthCopy = nullptr;
   const u32 currentFrame = gfx::current_frame();
   for (int i = 0; i < info.sampledTextures.size(); ++i) {
     if (!info.sampledTextures.test(i)) {
@@ -752,8 +753,11 @@ UniformRanges build_uniform(const ShaderInfo& info, u32 vtxStart, const BindGrou
     // CHECK(tex, "unbound texture {}", i);
     if (tex.ref && tex.ref->is_recent_efb_copy(currentFrame)) {
       samplesRecentEfbCopy = true;
-      samplesReducedEfbCopy =
-          samplesReducedEfbCopy || tex.texObj.width() * 2 <= kEfbWidth || tex.texObj.height() * 2 <= kEfbHeight;
+      const bool reduced = tex.texObj.width() * 2 <= kEfbWidth || tex.texObj.height() * 2 <= kEfbHeight;
+      samplesReducedEfbCopy = samplesReducedEfbCopy || reduced;
+      if (!perspective && !reduced && is_depth_format(tex.texObj.format())) {
+        compositeDepthCopy = tex.ref.get();
+      }
     }
     buf.append(texture_size_bias(tex));
   }
@@ -778,6 +782,8 @@ UniformRanges build_uniform(const ShaderInfo& info, u32 vtxStart, const BindGrou
                                  (drawViewport.width < static_cast<float>(fbWidth) * 0.9f ||
                                   drawViewport.height < static_cast<float>(fbHeight) * 0.9f);
 
+  const bool nativeEfbEffect =
+      !perspective && (readsDstAlpha || (samplesRecentEfbCopy && (samplesReducedEfbCopy || blends || offscreenViewport)));
   const UniformReplayLayout replayLayout{
       .projectionOffset = static_cast<uint32_t>(projectionOffset),
       .positionOffset = static_cast<uint32_t>(positionOffset),
@@ -787,8 +793,8 @@ UniformRanges build_uniform(const ShaderInfo& info, u32 vtxStart, const BindGrou
       .normalMatrixCount = layout.nrmCount,
       .perspective = perspective,
       .indexedMatrices = info.indexAttr.test(GX_VA_PNMTXIDX),
-      .nativeEfbEffect = !perspective && (readsDstAlpha || (samplesRecentEfbCopy &&
-                                                            (samplesReducedEfbCopy || blends || offscreenViewport))),
+      .nativeEfbEffect = nativeEfbEffect,
+      .compositeDepthCopy = nativeEfbEffect ? compositeDepthCopy : nullptr,
   };
 
   if (!perspective || !frame_interpolation_active()) {

aurora-main/lib/gx/shader_info.hpp

@@ -18,6 +18,16 @@ struct UniformReplayLayout {
   // rest of the native post-processing chain. It belongs to the rendered image,
   // not to the game's 2D layer, so it must stay where the game aimed it.
   bool nativeEfbEffect = false;
+  // For a native effect that samples a freshly produced, frame-sized depth copy: that
+  // copy. Mario Kart Wii draws a ghost kart alone into the cleared EFB, copies the
+  // frame's colour and depth out, draws the race, then blends the copies back with one
+  // such quad. Set when the draw is recorded; the pass that produced the copy holds the
+  // ghost's own perspective draws.
+  const gfx::TextureRef* compositeDepthCopy = nullptr;
+  // Index of that pass once the frame is sealed (link_composite_sources), or -1. An eye
+  // re-issues its perspective draws in this composite's place instead of stamping the
+  // desktop's flat image of the ghost over its own view.
+  int32_t compositeSourcePass = -1;
 };
 
 struct UniformRanges {

aurora-main/tests/gx_fifo_test.cpp

@@ -5246,3 +5246,73 @@ TEST_F(GXFifoTest, OffscreenViewportPassOverFreshCopyIsNativeEfbEffect) {
                                                      aurora::gx::FrameInterpolationDrawIdentity{}, false);
   EXPECT_FALSE(frameLayout.replayLayout.nativeEfbEffect);
 }
+
+TEST(GXPipelineConfig, StereoStencilFieldCarriesTheCompositeSourceBlendBit) {
+  aurora::gx::PipelineConfig config{};
+  config.stereoStencil = aurora::gx::kStereoStencilFormat | aurora::gx::kCompositeSourceBlend;
+  EXPECT_TRUE(aurora::gx::valid_pipeline_config(config));
+  config.stereoStencil = (aurora::gx::kStereoStencilFormat | aurora::gx::kCompositeSourceBlend) + 1;
+  EXPECT_FALSE(aurora::gx::valid_pipeline_config(config));
+}
+
+TEST_F(GXFifoTest, NativeCompositeRecordsTheFrameSizedDepthCopyItSamples) {
+  // Mario Kart Wii's ghost kart: one orthographic quad blends a frame-sized colour copy back
+  // over the race with the depth of a frame-sized depth copy. The layout names that depth copy so
+  // the eye replay can find the pass whose draws produced it.
+  // Frame-sized buffers: static so two of them do not exhaust the test thread's stack.
+  static std::array<u8, 608 * 456 * 4> colour{};
+  static std::array<u8, 608 * 456 * 4> depth{};
+  gxState().pixelFmt = GX_PF_RGBA6_Z24;
+  aurora::gfx::testing::set_framebuffer_sizes(640, 528, 640, 528);
+  aurora::gfx::testing::set_current_frame(50);
+
+  GXSetTexCopySrc(0, 0, 608, 456);
+  GXSetTexCopyDst(608, 456, GX_TF_Z24X8, GX_FALSE);
+  GXCopyTex(depth.data(), GX_TRUE);
+  GXSetTexCopyDst(608, 456, GX_TF_RGB565, GX_FALSE);
+  GXCopyTex(colour.data(), GX_TRUE);
+  const auto& records = aurora::gfx::testing::resolve_pass_records();
+  ASSERT_EQ(records.size(), 2u);
+  ASSERT_TRUE(records[0].texture);
+  ASSERT_TRUE(records[1].texture);
+
+  GXTexObj_ colourObj{};
+  colourObj.mWidth = 608;
+  colourObj.mHeight = 456;
+  colourObj.mFormat = GX_TF_RGB565;
+  GXTexObj_ depthObj{};
+  depthObj.mWidth = 608;
+  depthObj.mHeight = 456;
+  depthObj.mFormat = GX_TF_Z24X8;
+  gxState().textures[GX_TEXMAP0] = aurora::gfx::TextureBind{colourObj, records[1].texture};
+  gxState().textures[GX_TEXMAP1] = aurora::gfx::TextureBind{depthObj, records[0].texture};
+  gxState().blendMode = GX_BM_BLEND;
+  gxState().blendFacSrc = GX_BL_SRCALPHA;
+  gxState().blendFacDst = GX_BL_INVSRCALPHA;
+  gxState().logicalViewport = {0.0f, 0.0f, 640.0f, 528.0f, 0.0f, 1.0f};
+  aurora::gx::ShaderConfig shader{};
+  shader.numTexGens = 2;
+  shader.tevStageCount = 2;
+  shader.tevStages[0].texCoordId = GX_TEXCOORD0;
+  shader.tevStages[0].texMapId = GX_TEXMAP0;
+  shader.tevStages[0].colorPass.d = GX_CC_TEXC;
+  shader.tevStages[0].alphaPass.d = GX_CA_TEXA;
+  shader.tevStages[1].texCoordId = GX_TEXCOORD1;
+  shader.tevStages[1].texMapId = GX_TEXMAP1;
+  shader.tevStages[1].colorPass.d = GX_CC_TEXC;
+  shader.tevStages[1].alphaPass.d = GX_CA_TEXA;
+  const auto info = aurora::gx::build_shader_info(shader);
+
+  aurora::gfx::testing::reset_uniform_allocations();
+  const auto composite = aurora::gx::build_uniform(info, 0, aurora::gx::BindGroupRanges{},
+                                                   aurora::gx::FrameInterpolationDrawIdentity{}, false);
+  EXPECT_TRUE(composite.replayLayout.nativeEfbEffect);
+  EXPECT_EQ(composite.replayLayout.compositeDepthCopy, records[0].texture.get());
+  EXPECT_EQ(composite.replayLayout.compositeSourcePass, -1);
+
+  // The same draw with the game camera is world geometry, whatever it samples.
+  aurora::gfx::testing::reset_uniform_allocations();
+  const auto world = aurora::gx::build_uniform(info, 0, aurora::gx::BindGroupRanges{},
+                                               aurora::gx::FrameInterpolationDrawIdentity{}, true);
+  EXPECT_EQ(world.replayLayout.compositeDepthCopy, nullptr);
+}