如何确保在WebGPU中正确清除背景？

Question

当使用WebGPU渲染时，我需要设置一个神奇的标志来正确清除背景吗？我的渲染运行良好，除了，无论我使用什么设置，我看到最后显示的垃圾是在浏览器窗口中，而不是背景颜色(如果我在附件中设置了一个非零的clearColor，那么它将不断累积相同的颜色，直到它的max‘out)：

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我通过emscripten CPP接口使用WebGPU，并在Windows上运行Chrome Canary (版本90.0.4407.0 (官方版本) canary (64位))。

我的帧渲染看起来像这样(从js端的requestAnimationFrame调用)：

WGPUSwapChain swapChain                 = _pWindow->swapChain();
WGPUTextureView backbufferView          = wgpuSwapChainGetCurrentTextureView(swapChain);
WGPURenderPassDescriptor renderpassInfo = {};
WGPURenderPassColorAttachmentDescriptor colorAttachment = {};
{
    colorAttachment.attachment            = backbufferView;
    colorAttachment.resolveTarget         = nullptr;
    colorAttachment.clearColor            = { 0.0f, 0.0f, 0.0f, 0.0f };
    colorAttachment.loadOp                = WGPULoadOp_Clear;
    colorAttachment.storeOp               = WGPUStoreOp_Store;
    renderpassInfo.colorAttachmentCount   = 1;
    renderpassInfo.colorAttachments       = &colorAttachment;
    renderpassInfo.depthStencilAttachment = nullptr;
}
WGPUCommandBuffer commands;
{
    WGPUCommandEncoder encoder = wgpuDeviceCreateCommandEncoder(_device, nullptr);

    WGPURenderPassEncoder pass = wgpuCommandEncoderBeginRenderPass(encoder, &renderpassInfo);
    wgpuRenderPassEncoderSetPipeline(pass, _pipeline);
    wgpuRenderPassEncoderSetVertexBuffer(pass, 0, _vb, 0, 0);
    wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
    wgpuRenderPassEncoderEndPass(pass);
    wgpuRenderPassEncoderRelease(pass);

    
    commands = wgpuCommandEncoderFinish(encoder, nullptr);
    wgpuCommandEncoderRelease(encoder);
}

wgpuQueueSubmit(_queue, 1, &commands);
wgpuCommandBufferRelease(commands);
wgpuTextureViewRelease(backbufferView);

使用以下设置设置管道：

WGPURenderPipelineDescriptor descriptor = {};
WGPUBlendDescriptor blendDescriptor           = {};
blendDescriptor.operation                     = WGPUBlendOperation_Add;
blendDescriptor.srcFactor                     = WGPUBlendFactor_One;
blendDescriptor.dstFactor                     = WGPUBlendFactor_Zero;
WGPUColorStateDescriptor colorStateDescriptor = {};
colorStateDescriptor.format                   = _colorFormat;
colorStateDescriptor.alphaBlend               = blendDescriptor;
colorStateDescriptor.colorBlend               = blendDescriptor;
colorStateDescriptor.writeMask                = WGPUColorWriteMask_All;

descriptor.colorStateCount = 1;
descriptor.colorStates     = &colorStateDescriptor;

有没有我遗漏的设置，或者这是一个金丝雀bug？

Answer 1

有一个0的alpha值，这就把它搞乱了:(在clearColor字段中将它改为1可以很好地工作：

colorAttachment.clearColor            = { 0.0f, 0.0f, 0.0f, 1.0f };