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Allow transparent clear color if specified #69

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Allow transparent clear color if specified #69

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60 changes: 42 additions & 18 deletions src/dawn/native/vulkan/SwapChainVk.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -302,26 +302,50 @@ ResultOrError<SwapChain::Config> SwapChain::ChooseConfig(

config.transform = VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR;

config.alphaMode = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
#if !DAWN_PLATFORM_IS(ANDROID)
DAWN_INVALID_IF(
(surfaceInfo.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR) == 0,
"Vulkan SwapChain must support opaque alpha.");
#else
// TODO(dawn:286): investigate composite alpha for WebGPU native
VkCompositeAlphaFlagBitsKHR compositeAlphaFlags[4] = {
VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR,
VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR,
VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR,
VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR,
};
for (uint32_t i = 0; i < 4; i++) {
if (surfaceInfo.capabilities.supportedCompositeAlpha & compositeAlphaFlags[i]) {
config.alphaMode = compositeAlphaFlags[i];
break;
// Honor the WebGPU surface descriptor's alphaMode on all platforms.
// Previously the non-Android path hardcoded OPAQUE which silently
// dropped per-pixel transparency requests. See dawn:286.
{
VkCompositeAlphaFlagBitsKHR requestedVk = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
switch (GetAlphaMode()) {
case wgpu::CompositeAlphaMode::Premultiplied:
requestedVk = VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR;
break;
case wgpu::CompositeAlphaMode::Unpremultiplied:
requestedVk = VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR;
break;
case wgpu::CompositeAlphaMode::Inherit:
requestedVk = VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR;
break;
case wgpu::CompositeAlphaMode::Opaque:
case wgpu::CompositeAlphaMode::Auto:
default:
requestedVk = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
break;
}
if (surfaceInfo.capabilities.supportedCompositeAlpha & requestedVk) {
config.alphaMode = requestedVk;
} else {
// Fall back to the first supported mode — order chosen so
// OPAQUE is the last resort if the surface refuses it.
VkCompositeAlphaFlagBitsKHR fallbacks[4] = {
VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR,
VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR,
VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR,
VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR,
};
config.alphaMode = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
for (uint32_t i = 0; i < 4; i++) {
if (surfaceInfo.capabilities.supportedCompositeAlpha & fallbacks[i]) {
config.alphaMode = fallbacks[i];
break;
}
}
}
DAWN_INVALID_IF(
(surfaceInfo.capabilities.supportedCompositeAlpha & config.alphaMode) == 0,
"Vulkan SwapChain: no supported composite alpha mode.");
}
#endif // #if !DAWN_PLATFORM_IS(ANDROID)

// Choose the number of images for the swapchain= and clamp it to the min and max from the
// surface capabilities. maxImageCount = 0 means there is no limit.
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