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GPU: Support swapchain buffer transparency in Vulkan

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If the window is flagged with SDL_WINDOW_TRANSPARENT, create the associated swapchain with a composite alpha value that supports blending, if available.

Fixes transparent windows on the Vulkan backend, and prevents possible validation errors by ensuring that the composite alpha value is always a valid bit in VkSurfaceCapabilitiesKHR::supportedCompositeAlpha.
This commit is contained in:
Frank Praznik 2024-08-31 10:13:59 -04:00 • committed by Sam Lantinga
parent 79081a178f
commit bde49abdb7
1 changed files with 21 additions and 1 deletions
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22
src/gpu/vulkan/SDL_gpu_vulkan.c
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@ -4430,6 +4430,7 @@ static Uint32 VULKAN_INTERNAL_CreateSwapchain(
VkSemaphoreCreateInfo semaphoreCreateInfo;
SwapchainSupportDetails swapchainSupportDetails;
bool hasValidSwapchainComposition, hasValidPresentMode;
VkCompositeAlphaFlagsKHR compositeAlphaFlag = 0;
Uint32 i;
windowData->frameCounter = 0;
@ -4570,6 +4571,25 @@ static Uint32 VULKAN_INTERNAL_CreateSwapchain(
requestedImageCount = SDL_max(requestedImageCount, 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;
@ -4591,7 +4611,7 @@ static Uint32 VULKAN_INTERNAL_CreateSwapchain(
#else
swapchainCreateInfo.preTransform = swapchainSupportDetails.capabilities.currentTransform;
#endif
swapchainCreateInfo.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
swapchainCreateInfo.compositeAlpha = compositeAlphaFlag;
swapchainCreateInfo.presentMode = SDLToVK_PresentMode[windowData->presentMode];
swapchainCreateInfo.clipped = VK_TRUE;
swapchainCreateInfo.oldSwapchain = VK_NULL_HANDLE;