Flush onscreen texture to offscreen texture on context switches

packages/webgpu/cpp/rnwgpu/SurfaceRegistry.h

@@ -48,18 +48,42 @@ class SurfaceInfo {
  }
  }
 
- void *switchToOffscreen() {
+void *switchToOffscreen() {
  std::unique_lock<std::shared_mutex> lock(_mutex);
- wgpu::TextureDescriptor textureDesc;
- textureDesc.usage = wgpu::TextureUsage::RenderAttachment |
- wgpu::TextureUsage::CopySrc |
- wgpu::TextureUsage::TextureBinding;
- textureDesc.format = config.format;
- textureDesc.size.width = config.width;
- textureDesc.size.height = config.height;
- texture = config.device.CreateTexture(&textureDesc);
+ _createOffscreenTexture();
+
+ if (surface) {
+ // Copy the current surface texture to the offscreen texture
+ wgpu::CommandEncoderDescriptor encoderDesc;
+ wgpu::CommandEncoder encoder = config.device.CreateCommandEncoder(&encoderDesc);
+
+ wgpu::ImageCopyTexture sourceTexture = {};
+ wgpu::SurfaceTexture surfaceTexture;
+ surface.GetCurrentTexture(&surfaceTexture);
+ sourceTexture.texture = surfaceTexture.texture;
+
+ wgpu::ImageCopyTexture destinationTexture = {};
+ destinationTexture.texture = texture;
+
+ wgpu::Extent3D copySize = {
+ static_cast<uint32_t>(config.width),
+ static_cast<uint32_t>(config.height),
+ 1
+ };
+
+ encoder.CopyTextureToTexture(&sourceTexture, &destinationTexture, &copySize);
+
+ wgpu::CommandBuffer commands = encoder.Finish();
+ config.device.GetQueue().Submit(1, &commands);
+
+ // Unconfigure the surface
+ surface.Unconfigure();
+ }
+
+ void* oldNativeSurface = nativeSurface;
  surface = nullptr;
- return nativeSurface;
+ nativeSurface = nullptr;
+ return oldNativeSurface;
  }
 
  void switchToOnscreen(void *newNativeSurface, wgpu::Surface newSurface) {
@@ -69,7 +93,6 @@ class SurfaceInfo {
  // If we are comming from an offscreen context, we need to configure the new
  // surface
  if (texture != nullptr) {
- config.usage = config.usage | wgpu::TextureUsage::CopyDst;
  _configure();
  // We flush the offscreen texture to the onscreen one
  // TODO: there is a faster way to do this without validation?
@@ -146,19 +169,25 @@ class SurfaceInfo {
 private:
  void _configure() {
  if (surface) {
+ config.usage = config.usage | wgpu::TextureUsage::CopyDst | wgpu::TextureUsage::CopySrc;
  surface.Configure(&config);
  } else {
- wgpu::TextureDescriptor textureDesc;
- textureDesc.format = config.format;
- textureDesc.size.width = config.width;
- textureDesc.size.height = config.height;
- textureDesc.usage = wgpu::TextureUsage::RenderAttachment |
- wgpu::TextureUsage::CopySrc |
- wgpu::TextureUsage::TextureBinding;
- texture = config.device.CreateTexture(&textureDesc);
+ _createOffscreenTexture();
  }
  }
 
+ void _createOffscreenTexture() {
+ wgpu::TextureDescriptor textureDesc;
+ textureDesc.format = config.format;
+ textureDesc.size.width = config.width;
+ textureDesc.size.height = config.height;
+ textureDesc.usage = wgpu::TextureUsage::RenderAttachment |
+ wgpu::TextureUsage::CopySrc |
+ wgpu::TextureUsage::CopyDst |
+ wgpu::TextureUsage::TextureBinding;
+ texture = config.device.CreateTexture(&textureDesc);
+ }
+
  mutable std::shared_mutex _mutex;
  void *nativeSurface = nullptr;
  wgpu::Surface surface = nullptr;