Added foveated rendering for the Quest

- Eyes render under a VK_EXT_fragment_density_map: full rate around each eye's forward direction,
  2x2 then 4x4 pixel blocks towards the edges ([vr] foveation = off|low|medium|high, default off).
  XR_FB_foveation cannot help here: the runtime's maps only shape passes drawing into its
  swapchain, and the eyes reach it through a copy.
- aurora-main/patches/dawn/aurora_fdm.inc: Dawn enables the extension only on request and for
  dynamic rendering, flags every render pipeline, and chains an immutable RG8 map into any pass
  whose first color attachment is a view bound to one (ABI: include/aurora/dawn_fdm_abi.h).
- android/Build-QuestDawn.ps1 builds the pinned Dawn revision with those patches for arm64
  (dawn-build CI flags, protobuf off) into a cached package; Build-Quest.ps1 links it
  (-StockDawn opts out) and AuroraDawnProvider.cmake enables the ABI from its manifest.
- lib/gfx/foveation.hpp generates the maps (32 px per texel, densities 255/127/63); an eye is
  foveated only when single_pass_eyes draws it in one render pass. Menus never are.
- Live level from the headset panel's VR tab and the launcher; the launch decides whether the
  device has maps. debug.wiicompiled.foveation and debug.wiicompiled.fdm for A/B.
- Tests: Foveation cases in gx_fifo_tests, mkw_vr_config_tests. Docs: OPENXR.md, quest-port.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

runtime/src/settings_overlay.cpp

@@ -145,6 +145,11 @@ bool g_vrHudVirtualScreen = RuntimeConfigFile::VrHudVirtualScreen(true);
 bool g_vrFlatScreen = RuntimeConfigFile::VrFlatScreen();
 #if defined(__ANDROID__)
 bool g_vrPassthrough = RuntimeConfigFile::VrPassthrough();
+// Menu labels for the foveation levels, index-matched to RuntimeConfigFile::kVrFoveationLevels and to
+// aurora_set_stereo_foveation.
+constexpr std::array<const char*, 4> kVrFoveationLabels{"Off", "Low", "Medium", "High"};
+static_assert(kVrFoveationLabels.size() == RuntimeConfigFile::kVrFoveationLevels.size());
+int g_vrFoveation = static_cast<int>(RuntimeConfigFile::VrFoveationLevelIndex(RuntimeConfigFile::VrFoveation()));
 #endif
 bool g_vrFirstPerson = RuntimeConfigFile::VrFirstPerson(false);
 bool g_vrFirstPersonToggleClick = RuntimeConfigFile::VrFirstPersonToggleClick();
@@ -1512,6 +1517,25 @@ void DrawVrSettings() {
             "fully virtual; the Flat Screen race has the room around it too. "
             "Applies immediately.");
     }
+    // Shows the live level, which debug.wiicompiled.foveation can override.
+    g_vrFoveation = static_cast<int>(aurora_get_stereo_foveation());
+    if (ImGui::Combo("Foveated rendering", &g_vrFoveation, kVrFoveationLabels.data(),
+                     static_cast<int>(kVrFoveationLabels.size()))) {
+        aurora_set_stereo_foveation(static_cast<uint32_t>(g_vrFoveation));
+        RuntimeConfigFile::SetVrFoveation(
+            std::string(RuntimeConfigFile::kVrFoveationLevels[static_cast<size_t>(g_vrFoveation)]));
+    }
+    if (ImGui::IsItemHovered()) {
+        ImGui::SetTooltip(
+            "%s", aurora_stereo_foveation_available()
+                      ? "Shades the edges of the race view in 2x2, then 4x4 pixel blocks, where the "
+                        "lenses blur the picture anyway, to free GPU time for a higher render scale or a "
+                        "steadier frame rate. Higher levels start closer to the centre; High also "
+                        "coarsens the corners of the HUD. Menus are never foveated. Applies immediately."
+                      : "Shades the edges of the race view in 2x2, then 4x4 pixel blocks, where the "
+                        "lenses blur the picture anyway, to free GPU time. This session started with it "
+                        "off, or without a GPU that supports it: a new level applies after a restart.");
+    }
 #endif
     ImGui::Separator();
     ImGui::Text("VR camera");
@@ -2331,6 +2355,9 @@ void InitializeRuntimeSettings() noexcept {
     aurora_set_stereo_stop_at_display_copy(g_vrStopAtDisplayCopy);
     aurora_set_stereo_skip_copy_clears(g_vrSkipCopyClears);
     aurora_set_stereo_single_pass_eyes(g_vrSinglePassEyes);
+#if defined(__ANDROID__)
+    aurora_set_stereo_foveation(static_cast<uint32_t>(g_vrFoveation));
+#endif
     aurora_set_stereo_mirror_view(static_cast<AuroraStereoMirrorView>(g_vrMirrorView));
     mkw::vr::OpenXRSetControllerMode(static_cast<mkw::vr::OpenXRControllerMode>(g_vrControllerMode));
     ApplyVrHudVirtualScreen();

runtime/src/vr/openxr_integration.cpp

@@ -618,6 +618,11 @@ private:
     void ApplyGraphicsRequirements(AuroraConfig& aurora_config) {
         aurora_config.desiredBackend = kRequiredAuroraBackend;
         aurora_config.xrInterop = true;
+#if defined(__ANDROID__)
+        // Foveated rendering: fragment density maps are decided with the device. They put a flag on
+        // every render pipeline, so a session launched with foveation off does without them.
+        aurora_config.xrFragmentDensityMap = RuntimeConfigFile::VrFoveation() != "off";
+#endif
 #if defined(_WIN32)
         if (kRequiredAuroraBackend != BACKEND_D3D12) return;
         const auto& requirements = backend_->GraphicsRequirements();
@@ -851,6 +856,7 @@ private:
             const bool panel_layer = backend_->PanelLayerAvailable() && !PanelLayerForcedOff();
             aurora_set_stereo_panel_layer(panel_layer);
             PollEyePassesOverride();
+            PollFoveationOverride();
             presentation.panel.requested = panel_layer && OpenXRSettingsPanelOpen();
 
             // Pipeline caches are stored where their stall is least visible: once when a race
@@ -1481,6 +1487,39 @@ private:
 #endif
     }
 
+    // Android: `adb shell setprop debug.wiicompiled.foveation <0-3>` overrides the foveation level
+    // (off, low, medium, high) within one session, for A/B timing; an empty value hands it back to
+    // the settings. Levels need a session launched with foveation on (see VrFoveation). Read about
+    // once a second.
+    void PollFoveationOverride() noexcept {
+#if defined(__ANDROID__)
+        if (foveation_poll_ != 0) {
+            --foveation_poll_;
+            return;
+        }
+        foveation_poll_ = 72;
+        char value[PROP_VALUE_MAX] = {};
+        int override_value = -1;
+        if (__system_property_get("debug.wiicompiled.foveation", value) > 0 && value[0] >= '0' &&
+            value[0] <= '3' && value[1] == '\0') {
+            override_value = value[0] - '0';
+        }
+        if (override_value == foveation_override_) {
+            return;
+        }
+        foveation_override_ = override_value;
+        const uint32_t level = override_value >= 0
+                                   ? static_cast<uint32_t>(override_value)
+                                   : RuntimeConfigFile::VrFoveationLevelIndex(RuntimeConfigFile::VrFoveation());
+        aurora_set_stereo_foveation(level);
+        RT_LOG(RT_TAG_RUNTIME) << "OpenXR: foveation " << RuntimeConfigFile::kVrFoveationLevels[level]
+                               << (override_value >= 0 ? " (debug.wiicompiled.foveation)"
+                                                       : " (debug.wiicompiled.foveation cleared)")
+                               << (aurora_stereo_foveation_available() ? "" : "; unavailable in this session")
+                               << std::endl;
+#endif
+    }
+
     // The settings panel's layer hangs exactly where its pointer hits are
     // tested, the rectangle it used to cover in the eyes.
     static void PlacePanelLayer(OpenXRBackendFrame& frame, const OpenXRPointerScreen& screen) noexcept {
@@ -1706,6 +1745,8 @@ private:
     bool panel_layer_forced_off_ = false;
     uint32_t eye_passes_poll_ = 0;
     int eye_passes_override_ = -1;
+    uint32_t foveation_poll_ = 0;
+    int foveation_override_ = -1;
 #endif
     std::unique_ptr<OpenXRInput> input_;
     std::thread pacing_thread_;