Backends: Vulkan: helper for creating a swapchain selects VkSwapchainCreateInfoKHR's compositeAlpha based on cap.supportedCompositeAlpha. (#8784)

Author: ocornut

backends/imgui_impl_vulkan.cpp

@@ -27,6 +27,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-11-24: Vulkan: Helper for creating a swap-chain (used by examples and multi-viewports) selects VkSwapchainCreateInfoKHR's compositeAlpha based on cap.supportedCompositeAlpha. (#8784)
 //  2025-10-15: Vulkan: Added IMGUI_IMPL_VULKAN_VOLK_FILENAME to configure path to volk.h header. (#9008)
 //  2025-09-26: *BREAKING CHANGE*: moved some fields in ImGui_ImplVulkan_InitInfo: init_info.RenderPass --> init_info.PipelineInfoMain.RenderPass, init_info.Subpass --> init_info.PipelineInfoMain.Subpass, init_info.MSAASamples --> init_info.PipelineInfoMain.MSAASamples, init_info.PipelineRenderingCreateInfo --> init_info.PipelineInfoMain.PipelineRenderingCreateInfo.
 //  2025-09-26: *BREAKING CHANGE*: renamed ImGui_ImplVulkan_MainPipelineCreateInfo to ImGui_ImplVulkan_PipelineInfo. Introduced very recently so shouldn't affect many users.
@@ -1637,7 +1638,12 @@ void ImGui_ImplVulkanH_CreateWindowSwapChain(VkPhysicalDevice physical_device, V
         info.imageUsage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | image_usage;
         info.imageSharingMode = VK_SHARING_MODE_EXCLUSIVE;           // Assume that graphics family == present family
         info.preTransform = (cap.supportedTransforms & VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR) ? VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR : cap.currentTransform;
-        info.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
+        if (cap.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR)
+            info.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
+        else if (cap.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR)
+            info.compositeAlpha = VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR;
+        else
+            IM_ASSERT(false && "No supported composite alpha mode found!");
         info.presentMode = wd->PresentMode;
         info.clipped = VK_TRUE;
         info.oldSwapchain = old_swapchain;

docs/CHANGELOG.txt

@@ -50,6 +50,10 @@ Other Changes:
   the oldest bug in Dear ImGui history (albeit for a rarely used feature)! (#9086)
 - Scrollbar: fixed a codepath leading to a divide-by-zero (which would not be
   noticeable by user but detected by sanitizers). (#9089) [@judicaelclair]
+- Backends:
+  - Vulkan: helper for creating a swapchain (used by examples and multi-viewports)
+    selects `VkSwapchainCreateInfoKHR`'s `compositeAlpha` value based on
+    `cap.supportedCompositeAlpha`. (#8784) [@FelixStach]
 
 
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