Add adaptive resolution for the immersive eyes

[vr] adaptive_resolution (off by default, in the VR tab) lowers the
race's eye resolution by 10% steps, down to 70%, while new eye frames
fall below 85% of the game's 60 FPS, and raises it again after three
seconds on time. Adapted from heurazy/Wiicompiled_VR-PLUS.

The eyes render into the top-left corner of the full swapchain image
and the projection layer shows only that corner, so the compositor
upscales them and no swapchain is recreated, unlike render_scale. The
Linux same-device bridge now copies an eye smaller than its target;
the Quest's bridge and layer already did. The PC's D3D12 path copies
whole eyes, so the setting is not offered on Windows.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sabhzu6VgoWcHtpSk4C9KZ

runtime/include/runtime_config.h

@@ -101,6 +101,7 @@ struct RuntimeUserConfig {
     std::optional<std::string> vrFoveation;
     std::optional<bool> vrEyeTrackedFoveation;
     std::optional<bool> vrRepeatFrames;
+    std::optional<bool> vrAdaptiveResolution;
     std::optional<std::string> vrRecenterKey;
     std::optional<float> vrLeanBackDegrees;
     // F10 > Diagnostics: OpenXR pacing and presentation logging in console.log.
@@ -607,6 +608,10 @@ inline void EnsureConfigFile() {
               "# Submit the last frame again for each refresh the game has no new\n"
               "# frame for, so the runtime does not fill those refreshes itself. Live.\n"
               "repeat_frames = " MKW_VR_REPEAT_FRAMES_DEFAULT_TOML "\n"
+              "# Lower the race's eye resolution, down to 70% of render_scale, while\n"
+              "# new frames fall behind the game's 60 FPS, and raise it again once\n"
+              "# they keep up. Experimental; the Steam Frame and the Quest. Live.\n"
+              "adaptive_resolution = false\n"
               "render_scale = " MKW_VR_RENDER_SCALE_DEFAULT_TEXT "\n"
               "world_units_per_meter = 500.0\n"
               "hud_distance_meters = 2.0\n"
@@ -928,6 +933,7 @@ inline RuntimeUserConfig ParseConfigDocument(const toml::value& document) {
     }
     config.vrEyeTrackedFoveation = FindConfigValue<bool>(document, "vr", "eye_tracked_foveation");
     config.vrRepeatFrames = FindConfigValue<bool>(document, "vr", "repeat_frames");
+    config.vrAdaptiveResolution = FindConfigValue<bool>(document, "vr", "adaptive_resolution");
     if (auto value = FindConfigValue<std::string>(document, "vr", "mirror_view");
         value && IsSupportedVrMirrorView(*value)) {
         config.vrMirrorView = *value;
@@ -1345,6 +1351,11 @@ inline bool SetVrRepeatFrames(bool value) {
     return WriteSetting("vr", "repeat_frames", value ? "true" : "false");
 }
 
+inline bool SetVrAdaptiveResolution(bool value) {
+    Mutable().vrAdaptiveResolution = value;
+    return WriteSetting("vr", "adaptive_resolution", value ? "true" : "false");
+}
+
 inline bool SetVrEyeTrackedFoveation(bool value) {
     Mutable().vrEyeTrackedFoveation = value;
     return WriteSetting("vr", "eye_tracked_foveation", value ? "true" : "false");
@@ -1880,6 +1891,10 @@ inline bool VrRepeatFrames(bool fallback = kVrRepeatFramesDefault) {
     return Get().vrRepeatFrames.value_or(fallback);
 }
 
+inline bool VrAdaptiveResolution(bool fallback = false) {
+    return Get().vrAdaptiveResolution.value_or(fallback);
+}
+
 inline bool VrEyeTrackedFoveation(bool fallback = kVrEyeTrackedFoveationDefault) {
     return Get().vrEyeTrackedFoveation.value_or(fallback);
 }