Backends: Vulkan: Replaced InitInfo's PipelineInfo PipelineInfoForViewports by SecondaryViewportsInfo SecondaryViewportsInfo

- `PipelineInfoForViewports` was confusing (only one (or two) out of the five (or six) parameters was actually used).
- Add `struct ImGui_ImplVulkan_SecondaryViewportsInfo` for viewports specific informations (to be extended and re-used)

Author: SuperRonan

backends/imgui_impl_vulkan.cpp

@@ -282,7 +282,6 @@ struct ImGui_ImplVulkan_Data
     VkDescriptorSetLayout       DescriptorSetLayout;
     VkPipelineLayout            PipelineLayout;
     VkPipeline                  Pipeline;               // pipeline for main render pass (created by app)
-    VkPipeline                  PipelineForViewports;   // pipeline for secondary viewports (created by backend)
     VkShaderModule              ShaderModuleVert;
     VkShaderModule              ShaderModuleFrag;
     VkDescriptorPool            DescriptorPool;
@@ -296,6 +295,12 @@ struct ImGui_ImplVulkan_Data
     // Render buffers for main window
     ImGui_ImplVulkan_WindowRenderBuffers MainWindowRenderBuffers;
 
+    // Viewports common data
+    // Filled during ImGui_ImplVulkan_PrepareViewportsRendering() based on ViewportsFormat and VulkanInitInfo->SecondaryViewportsInfo
+    ImGui_ImplVulkan_PipelineInfo PipelineInfoForViewports;
+    VkPipeline                  PipelineForViewports;   // pipeline for secondary viewports (created by backend)
+
+
     ImGui_ImplVulkan_Data()
     {
         memset((void*)this, 0, sizeof(*this));
@@ -1321,7 +1326,7 @@ bool    ImGui_ImplVulkan_Init(ImGui_ImplVulkan_InitInfo* info)
     else
         IM_ASSERT(info->DescriptorPoolSize > 0);
     if (info->UseDynamicRendering)
-        IM_ASSERT(info->PipelineInfoMain.RenderPass == VK_NULL_HANDLE && info->PipelineInfoForViewports.RenderPass == VK_NULL_HANDLE);
+        IM_ASSERT(info->PipelineInfoMain.RenderPass == VK_NULL_HANDLE);
 
     bd->VulkanInitInfo = *info;
 
@@ -1978,18 +1983,18 @@ static void ImGui_ImplVulkan_CreateWindow(ImGuiViewport* viewport)
     }
 
     // Select Surface Format
-    ImGui_ImplVulkan_PipelineInfo* pipeline_info = &v->PipelineInfoForViewports;
-    ImVector<VkFormat> requestSurfaceImageFormats;
-#ifdef IMGUI_IMPL_VULKAN_HAS_DYNAMIC_RENDERING
-    for (uint32_t n = 0; n < pipeline_info->PipelineRenderingCreateInfo.colorAttachmentCount; n++)
-        requestSurfaceImageFormats.push_back(pipeline_info->PipelineRenderingCreateInfo.pColorAttachmentFormats[n]);
-#endif
-    const VkFormat defaultFormats[] = { VK_FORMAT_B8G8R8A8_UNORM, VK_FORMAT_R8G8B8A8_UNORM, VK_FORMAT_B8G8R8_UNORM, VK_FORMAT_R8G8B8_UNORM };
-    for (VkFormat format : defaultFormats)
-        requestSurfaceImageFormats.push_back(format);
+    ImGui_ImplVulkan_PipelineInfo* pipeline_info = &bd->PipelineInfoForViewports;
+    const VkFormat requestSurfaceImageFormats[] = { v->SecondaryViewportsInfo.DesiredFormat.format, VK_FORMAT_B8G8R8A8_UNORM, VK_FORMAT_R8G8B8A8_UNORM, VK_FORMAT_B8G8R8_UNORM, VK_FORMAT_R8G8B8_UNORM };
+    int requestSurfaceImageFormatsCount = IM_ARRAYSIZE(requestSurfaceImageFormats);
+    const VkFormat* pRequestSurfaceImageFormats = requestSurfaceImageFormats;
+    if (pRequestSurfaceImageFormats[0] == VK_FORMAT_UNDEFINED)
+    {
+        ++pRequestSurfaceImageFormats;
+        --requestSurfaceImageFormatsCount;
+    }
 
-    const VkColorSpaceKHR requestSurfaceColorSpace = VK_COLORSPACE_SRGB_NONLINEAR_KHR;
-    wd->SurfaceFormat = ImGui_ImplVulkanH_SelectSurfaceFormat(v->PhysicalDevice, wd->Surface, requestSurfaceImageFormats.Data, (size_t)requestSurfaceImageFormats.Size, requestSurfaceColorSpace);
+    const VkColorSpaceKHR requestSurfaceColorSpace = v->SecondaryViewportsInfo.DesiredFormat.colorSpace;
+    wd->SurfaceFormat = ImGui_ImplVulkanH_SelectSurfaceFormat(v->PhysicalDevice, wd->Surface, pRequestSurfaceImageFormats, requestSurfaceImageFormatsCount, requestSurfaceColorSpace);
 
     // Select Present Mode
     // FIXME-VULKAN: Even thought mailbox seems to get us maximum framerate with a single window, it halves framerate with a second window etc. (w/ Nvidia and SDK 1.82.1)
@@ -2000,7 +2005,7 @@ static void ImGui_ImplVulkan_CreateWindow(ImGuiViewport* viewport)
     // Create SwapChain, RenderPass, Framebuffer, etc.
     wd->ClearEnable = (viewport->Flags & ImGuiViewportFlags_NoRendererClear) ? false : true;
     wd->UseDynamicRendering = v->UseDynamicRendering;
-    ImGui_ImplVulkanH_CreateOrResizeWindow(v->Instance, v->PhysicalDevice, v->Device, wd, v->QueueFamily, v->Allocator, (int)viewport->Size.x, (int)viewport->Size.y, v->MinImageCount, pipeline_info->SwapChainImageUsage);
+    ImGui_ImplVulkanH_CreateOrResizeWindow(v->Instance, v->PhysicalDevice, v->Device, wd, v->QueueFamily, v->Allocator, (int)viewport->Size.x, (int)viewport->Size.y, v->MinImageCount, v->SecondaryViewportsInfo.SwapChainImageUsage);
     vd->WindowOwned = true;
 
     // Create pipeline (shared by all secondary viewports)
@@ -2018,7 +2023,7 @@ static void ImGui_ImplVulkan_CreateWindow(ImGuiViewport* viewport)
             pipeline_info->RenderPass = wd->RenderPass;
         }
 #endif
-        bd->PipelineForViewports = ImGui_ImplVulkan_CreatePipeline(v->Device, v->Allocator, VK_NULL_HANDLE, &v->PipelineInfoForViewports);
+        bd->PipelineForViewports = ImGui_ImplVulkan_CreatePipeline(v->Device, v->Allocator, VK_NULL_HANDLE, pipeline_info);
     }
 }
 
@@ -2045,7 +2050,7 @@ static void ImGui_ImplVulkan_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
         return;
     ImGui_ImplVulkan_InitInfo* v = &bd->VulkanInitInfo;
     vd->Window.ClearEnable = (viewport->Flags & ImGuiViewportFlags_NoRendererClear) ? false : true;
-    ImGui_ImplVulkanH_CreateOrResizeWindow(v->Instance, v->PhysicalDevice, v->Device, &vd->Window, v->QueueFamily, v->Allocator, (int)size.x, (int)size.y, v->MinImageCount, v->PipelineInfoForViewports.SwapChainImageUsage);
+    ImGui_ImplVulkanH_CreateOrResizeWindow(v->Instance, v->PhysicalDevice, v->Device, &vd->Window, v->QueueFamily, v->Allocator, (int)size.x, (int)size.y, v->MinImageCount, v->SecondaryViewportsInfo.SwapChainImageUsage);
 }
 
 static void ImGui_ImplVulkan_RenderWindow(ImGuiViewport* viewport, void*)
@@ -2058,7 +2063,7 @@ static void ImGui_ImplVulkan_RenderWindow(ImGuiViewport* viewport, void*)
 
     if (vd->SwapChainNeedRebuild || vd->SwapChainSuboptimal)
     {
-        ImGui_ImplVulkanH_CreateOrResizeWindow(v->Instance, v->PhysicalDevice, v->Device, wd, v->QueueFamily, v->Allocator, (int)viewport->Size.x, (int)viewport->Size.y, v->MinImageCount, v->PipelineInfoForViewports.SwapChainImageUsage);
+        ImGui_ImplVulkanH_CreateOrResizeWindow(v->Instance, v->PhysicalDevice, v->Device, wd, v->QueueFamily, v->Allocator, (int)viewport->Size.x, (int)viewport->Size.y, v->MinImageCount, v->SecondaryViewportsInfo.SwapChainImageUsage);
         vd->SwapChainNeedRebuild = vd->SwapChainSuboptimal = false;
     }
 

backends/imgui_impl_vulkan.h

@@ -66,7 +66,7 @@
 // Backend uses a small number of descriptors per font atlas + as many as additional calls done to ImGui_ImplVulkan_AddTexture().
 #define IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE   (8)     // Minimum per atlas
 
-// Specify settings to create pipeline and swapchain
+// Specify settings to create pipeline
 struct ImGui_ImplVulkan_PipelineInfo
 {
     // For Main viewport only
@@ -78,8 +78,13 @@ struct ImGui_ImplVulkan_PipelineInfo
 #ifdef IMGUI_IMPL_VULKAN_HAS_DYNAMIC_RENDERING
     VkPipelineRenderingCreateInfoKHR PipelineRenderingCreateInfo;   // Optional, valid if .sType == VK_STRUCTURE_TYPE_PIPELINE_RENDERING_CREATE_INFO_KHR
 #endif
+};
+
+struct ImGui_ImplVulkan_SecondaryViewportsInfo
+{
+    // Ignored if .format == VK_FORMAT_UNDEFINED
+    VkSurfaceFormatKHR              DesiredFormat;
 
-    // For Secondary viewports only (created/managed by backend)
     VkImageUsageFlags               SwapChainImageUsage;            // Extra flags for vkCreateSwapchainKHR() calls for secondary viewports. We automatically add VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT. You can add e.g. VK_IMAGE_USAGE_TRANSFER_SRC_BIT if you need to capture from viewports.
 };
 
@@ -107,7 +112,6 @@ struct ImGui_ImplVulkan_InitInfo
 
     // Pipeline
     ImGui_ImplVulkan_PipelineInfo   PipelineInfoMain;           // Infos for Main Viewport (created by app/user)
-    ImGui_ImplVulkan_PipelineInfo   PipelineInfoForViewports;   // Infos for Secondary Viewports (created by backend)
     //VkRenderPass                  RenderPass;                 // --> Since 2025/09/26: set 'PipelineInfoMain.RenderPass' instead
     //uint32_t                      Subpass;                    // --> Since 2025/09/26: set 'PipelineInfoMain.Subpass' instead
     //VkSampleCountFlagBits         MSAASamples;                // --> Since 2025/09/26: set 'PipelineInfoMain.MSAASamples' instead
@@ -117,6 +121,9 @@ struct ImGui_ImplVulkan_InitInfo
     // Need to explicitly enable VK_KHR_dynamic_rendering extension to use this, even for Vulkan 1.3 + setup PipelineInfoMain.PipelineRenderingCreateInfo and PipelineInfoViewports.PipelineRenderingCreateInfo.
     bool                            UseDynamicRendering;
 
+    // Optional
+    ImGui_ImplVulkan_SecondaryViewportsInfo SecondaryViewportsInfo;
+
     // (Optional) Allocation, Debugging
     const VkAllocationCallbacks*    Allocator;
     void                            (*CheckVkResultFn)(VkResult err);