Fix a few issues around readTexture and iOS camera

Core/Graphics/Source/DeviceImpl.cpp

@@ -173,6 +173,14 @@ namespace Babylon::Graphics
 
         if (m_state.Bgfx.Initialized)
         {
+            // Drain readTextures queue, completing them in an error state.
+            while (!m_readTextureRequests.empty())
+            {
+                auto error = arcana::make_unexpected(std::make_exception_ptr(std::system_error(std::make_error_code(std::errc::operation_canceled))));
+                m_readTextureRequests.front().second.complete(error);
+                m_readTextureRequests.pop();
+            }
+
             // HACK: Render one more frame to drain the before/after render work queues.
             StartRenderingCurrentFrame();
             FinishRenderingCurrentFrame();
@@ -390,8 +398,7 @@ namespace Babylon::Graphics
         uint32_t frameNumber{bgfx::frame()};
 
         // Process read texture requests.
-        assert(m_readTextureRequests.empty() || m_readTextureRequests.front().first >= frameNumber);
-        while (!m_readTextureRequests.empty() && m_readTextureRequests.front().first == frameNumber)
+        while (!m_readTextureRequests.empty() && m_readTextureRequests.front().first <= frameNumber)
         {
             m_readTextureRequests.front().second.complete();
             m_readTextureRequests.pop();

Plugins/NativeCamera/Source/Apple/NativeCameraImpl.mm

@@ -189,11 +189,12 @@ fragment float4 fragmentShader(RasterizerData in [[stage_in]],
 
         __block arcana::task_completion_source<Camera::Impl::CameraDimensions, std::exception_ptr> taskCompletionSource{};
 
-        dispatch_sync(dispatch_get_main_queue(), ^{
+        dispatch_async(dispatch_get_main_queue(), ^{
             CVMetalTextureCacheCreate(nullptr, nullptr, m_implData->metalDevice, nullptr, &m_implData->textureCache);
             m_implData->cameraTextureDelegate = [[CameraTextureDelegate alloc]init:m_implData];
             m_implData->avCaptureSession = [[AVCaptureSession alloc] init];
-
+            m_implData->textureRGBA = nil;
+
 #if (TARGET_OS_IPHONE)
             // Loop over all available camera configurations to find a config that most closely matches the constraints.
             AVCaptureDevice* bestDevice{nullptr};
@@ -395,9 +396,14 @@ fragment float4 fragmentShader(RasterizerData in [[stage_in]],
                 width = [textureY width];
                 height = [textureY height];
             }
+
+            // Skip processing this frame if width and height are invalid.
+            if (width == 0 || height == 0) {
+                return;
+            }
 
             // Recreate the output texture when the camera dimensions change.
-            if (m_cameraDimensions.width != width || m_cameraDimensions.height != height)
+            if (m_implData->textureRGBA == nil || m_cameraDimensions.width != width || m_cameraDimensions.height != height)
             {
                 MTLTextureDescriptor *textureDescriptor = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatRGBA8Unorm width:width height:height mipmapped:NO];
                 textureDescriptor.usage = MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead;
@@ -457,7 +463,7 @@ fragment float4 fragmentShader(RasterizerData in [[stage_in]],
 
     void Camera::Impl::Close()
     {
-        m_implData.reset();
+        m_implData.reset(new ImplData);
     }
 }
 

Plugins/NativeCapture/Source/NativeCapture.cpp

@@ -90,6 +90,7 @@ namespace
                     // Reading the texture is an async operation, but everything that needs to be done prior to future write operations on that texture is completed synchronously,
                     // so we kick off the read for the next frame prior to the read for the current frame completes.
 
+                    // TODO: #1131 Address potential race condition during engine shutdown and ReadTextureAsync.
                     arcana::task<void, std::exception_ptr> readCurrentFrameTask{thisRef->m_graphicsContext.ReadTextureAsync(thisRef->m_blitTextureHandle, thisRef->m_textureBuffer)
                         .then(arcana::inline_scheduler, thisRef->m_cancellationToken, [thisRef] {
                             thisRef->m_frameCallback(thisRef->m_textureInfo.Width, thisRef->m_textureInfo.Height, thisRef->m_textureInfo.Format, bgfx::getCaps()->originBottomLeft, thisRef->m_textureBuffer);