More robust alpha mode support

packages/webgpu/cpp/rnwgpu/SurfaceRegistry.h

@@ -154,6 +154,21 @@ class SurfaceInfo {
 private:
   void _configure() {
     if (surface) {
+      wgpu::SurfaceCapabilities capabilities;
+      surface.GetCapabilities(&capabilities);
+
+      // Check if requested alpha mode is supported
+      bool alphaModeSupported = false;
+      for (size_t i = 0; i < capabilities.alphaModeCount; i++) {
+          if (capabilities.alphaModes[i] == config.alphaMode) {
+              alphaModeSupported = true;
+              break;
+          }
+      }
+      // Revert to Auto if requested mode is not supported
+      if (!alphaModeSupported) {
+          config.alphaMode = wgpu::CompositeAlphaMode::Auto;
+      }
       surface.Configure(&config);
     } else {
       wgpu::TextureDescriptor textureDesc;

packages/webgpu/cpp/rnwgpu/api/GPUCanvasContext.cpp

@@ -20,10 +20,7 @@ void GPUCanvasContext::configure(
       !conv(surfaceConfiguration.format, configuration->format)) {
     throw std::runtime_error("Error with SurfaceConfiguration");
   }
-
-#ifdef __APPLE__
   surfaceConfiguration.alphaMode = configuration->alphaMode;
-#endif
   _surfaceInfo->configure(surfaceConfiguration);
 }