Re: Screen Capture using `CopyTextureToBuffer `. WGPUBufferMapAsyncStatus set to error.

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Kai Ninomiya

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Feb 2, 2023, 2:17:35 PMFeb 2
to Jean-Colas Prunier, Dawn Graphics

-Kai (he/they)


On Thu, Feb 2, 2023 at 7:54 AM Jean-Colas Prunier <j...@jean-colas.com> wrote:
I wanted to test ` CopyTextureToBuffer` functionality but have totally failed so far. I have been using the code below, which I copied for the most part from `CopyCommandValidationTests`. 

When I look at the value of `WGPUBufferMapAsyncStatus` in SaveToFile the callback function called by  ` MapAsync` I constantly get an error message.

- I create a basic texture (empty)
- Create a buffer to get copy the data to
- use  CopyTextureToBuffer for the cmd
- push the command to the queue.
- call  MapAsync on the buffer so that it calls SaveToFile once the command has been fully executed.

I would appreciate your input as to what I need to do better here (if that's obvious) or how I should be doing it. Thank you.

```
void CaptureScreen()
{  
    uint64_t offset = 0;
    uint32_t bytesPerRow = sizeof(unsigned char) * newSize.width * 3;
    uint32_t rowsPerImage = newSize.height;
    
    // these 2 are globals
    bufferSize = BufferSizeForTextureCopy(newSize.width, newSize.height, 1);
    destination = CreateBuffer(bufferSize, wgpu::BufferUsage::CopyDst);
In order to map this buffer later, it must be created with the MapRead usage as well (wgpu::BufferUsage::CopyDst | wgpu::BufferUsage::MapRead).

MapAsync should have generated a textual error message in the form of a validation error. If you haven't, you should set up a handler to print uncaptured validation errors, like so:
https://source.chromium.org/chromium/chromium/src/+/main:third_party/dawn/src/dawn/samples/ManualSwapChainTest.cpp;l=291;drc=52cc4f5d1c2840f0ac05cdfed87e9167df6607fb


    wgpu::ImageCopyBuffer imageCopyBuffer = CreateImageCopyBuffer(destination, offset, bytesPerRow, rowsPerImage);

    wgpu::Texture source = Create2DTexture(device, wgpu::TextureDimension::e2D,
        kColorFormat, newSize.width, newSize.width, 1, 1, 1);

    wgpu::ImageCopyTexture imageCopyTexture = CreateImageCopyTexture( source , 1, {0, 0, 0});
    wgpu::Extent3D extent3D = {width, height, 1};

    wgpu::CommandEncoder encoder = device.CreateCommandEncoder();
    encoder.CopyTextureToBuffer(&imageCopyTexture, &imageCopyBuffer, &extent3D);
    wgpu::CommandBuffer commands = encoder.Finish();
    device.GetQueue().Submit(1, &commands);

    destination.MapAsync(wgpu::MapMode::Read, 0, bufferSize, SaveToFile, nullptr);
}
```

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Kai Ninomiya

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Feb 2, 2023, 2:18:52 PMFeb 2
to Jean-Colas Prunier, Dawn Graphics
Sorry, I just saw there was already a reply to this. Somehow the `backticks` in the subject line caused the thread to fork.
-Kai (he/they)

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