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GPU: Support swapchain buffer transparency in Vulkan #10654

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GPU: Support swapchain buffer transparency in Vulkan #10654

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22 changes: 21 additions & 1 deletion src/gpu/vulkan/SDL_gpu_vulkan.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4413,6 +4413,7 @@ static bool VULKAN_INTERNAL_CreateSwapchain(
VkSemaphoreCreateInfo semaphoreCreateInfo;
SwapchainSupportDetails swapchainSupportDetails;
bool hasValidSwapchainComposition, hasValidPresentMode;
VkCompositeAlphaFlagsKHR compositeAlphaFlag = 0;
Sint32 drawableWidth, drawableHeight;
Uint32 i;
SDL_VideoDevice *_this = SDL_GetVideoDevice();
Expand Down Expand Up @@ -4584,6 +4585,25 @@ static bool VULKAN_INTERNAL_CreateSwapchain(
swapchainData->imageCount = SDL_max(swapchainData->imageCount, 3);
}

// Default to opaque, if available, followed by inherit, and overwrite with a value that supports transparency, if necessary.
if (swapchainSupportDetails.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR) {
compositeAlphaFlag = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
} else if (swapchainSupportDetails.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR) {
compositeAlphaFlag = VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR;
}

if ((windowData->window->flags & SDL_WINDOW_TRANSPARENT) || !compositeAlphaFlag) {
if (swapchainSupportDetails.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR) {
compositeAlphaFlag = VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR;
} else if (swapchainSupportDetails.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR) {
compositeAlphaFlag = VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR;
} else if (swapchainSupportDetails.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR) {
compositeAlphaFlag = VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR;
} else {
SDL_LogWarn(SDL_LOG_CATEGORY_GPU, "SDL_WINDOW_TRANSPARENT flag set, but no suitable swapchain composite alpha value supported!");
}
}

swapchainCreateInfo.sType = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR;
swapchainCreateInfo.pNext = NULL;
swapchainCreateInfo.flags = 0;
Expand All @@ -4601,7 +4621,7 @@ static bool VULKAN_INTERNAL_CreateSwapchain(
swapchainCreateInfo.queueFamilyIndexCount = 0;
swapchainCreateInfo.pQueueFamilyIndices = NULL;
swapchainCreateInfo.preTransform = swapchainSupportDetails.capabilities.currentTransform;
swapchainCreateInfo.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
swapchainCreateInfo.compositeAlpha = compositeAlphaFlag;
swapchainCreateInfo.presentMode = swapchainData->presentMode;
swapchainCreateInfo.clipped = VK_TRUE;
swapchainCreateInfo.oldSwapchain = VK_NULL_HANDLE;
Expand Down
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