Backends: Vulkan: Explicitly enforce that secondary viewports share the same surface format.

- Add `ImGui_ImplVulkan_PrepareViewportsRendering(VkSurfaceKHR)` for later re-usability

Author: SuperRonan

backends/imgui_impl_vulkan.cpp

@@ -296,6 +296,7 @@ struct ImGui_ImplVulkan_Data
     ImGui_ImplVulkan_WindowRenderBuffers MainWindowRenderBuffers;
 
     // Viewports common data
+    VkSurfaceFormatKHR          ViewportsFormat;        // Common for all viewports, may differ from VulkanInitInfo.SecondaryViewportsInfo.DesiredFormat
     // Filled during ImGui_ImplVulkan_PrepareViewportsRendering() based on ViewportsFormat and VulkanInitInfo->SecondaryViewportsInfo
     ImGui_ImplVulkan_PipelineInfo PipelineInfoForViewports;
     VkPipeline                  PipelineForViewports;   // pipeline for secondary viewports (created by backend)
@@ -1219,8 +1220,15 @@ void    ImGui_ImplVulkan_DestroyDeviceObjects()
     if (bd->DescriptorSetLayout)  { vkDestroyDescriptorSetLayout(v->Device, bd->DescriptorSetLayout, v->Allocator); bd->DescriptorSetLayout = VK_NULL_HANDLE; }
     if (bd->PipelineLayout)       { vkDestroyPipelineLayout(v->Device, bd->PipelineLayout, v->Allocator); bd->PipelineLayout = VK_NULL_HANDLE; }
     if (bd->Pipeline)             { vkDestroyPipeline(v->Device, bd->Pipeline, v->Allocator); bd->Pipeline = VK_NULL_HANDLE; }
-    if (bd->PipelineForViewports) { vkDestroyPipeline(v->Device, bd->PipelineForViewports, v->Allocator); bd->PipelineForViewports = VK_NULL_HANDLE; }
     if (bd->DescriptorPool)       { vkDestroyDescriptorPool(v->Device, bd->DescriptorPool, v->Allocator); bd->DescriptorPool = VK_NULL_HANDLE; }
+
+    // Destroy viewports common objects
+    if (bd->PipelineForViewports) { vkDestroyPipeline(v->Device, bd->PipelineForViewports, v->Allocator); bd->PipelineForViewports = VK_NULL_HANDLE; }
+    if (bd->PipelineInfoForViewports.RenderPass)
+    {
+        vkDestroyRenderPass(v->Device, bd->PipelineInfoForViewports.RenderPass, v->Allocator);
+        bd->PipelineInfoForViewports.RenderPass = VK_NULL_HANDLE;
+    }
 }
 
 #ifdef IMGUI_IMPL_VULKAN_HAS_DYNAMIC_RENDERING
@@ -1980,28 +1988,15 @@ static void ImGui_ImplVulkan_SelectPresentMode(ImGuiViewport* viewport)
     //printf("[vulkan] Secondary window selected PresentMode = %d\n", wd->PresentMode);
 }
 
-static void ImGui_ImplVulkan_CreateWindow(ImGuiViewport* viewport)
+// Prepare common viewports rendering objects.
+// Requires a sample surface (assuming any viewport surface behaves the same).
+// - Select a surface format
+// - Create the common RenderPass and Pipeline
+static void ImGui_ImplVulkan_PrepareViewportsRendering(VkSurfaceKHR surface)
 {
     ImGui_ImplVulkan_Data* bd = ImGui_ImplVulkan_GetBackendData();
-    ImGui_ImplVulkan_ViewportData* vd = IM_NEW(ImGui_ImplVulkan_ViewportData)();
-    viewport->RendererUserData = vd;
-    ImGui_ImplVulkanH_Window* wd = &vd->Window;
     ImGui_ImplVulkan_InitInfo* v = &bd->VulkanInitInfo;
 
-    // Create surface
-    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
-    VkResult err = (VkResult)platform_io.Platform_CreateVkSurface(viewport, (ImU64)v->Instance, (const void*)v->Allocator, (ImU64*)&wd->Surface);
-    check_vk_result(err);
-
-    // Check for WSI support
-    VkBool32 res;
-    vkGetPhysicalDeviceSurfaceSupportKHR(v->PhysicalDevice, v->QueueFamily, wd->Surface, &res);
-    if (res != VK_TRUE)
-    {
-        IM_ASSERT(0); // Error: no WSI support on physical device
-        return;
-    }
-
     // Select Surface 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 };
@@ -2014,36 +2009,68 @@ static void ImGui_ImplVulkan_CreateWindow(ImGuiViewport* viewport)
     }
 
     const VkColorSpaceKHR requestSurfaceColorSpace = v->SecondaryViewportsInfo.DesiredFormat.colorSpace;
-    wd->SurfaceFormat = ImGui_ImplVulkanH_SelectSurfaceFormat(v->PhysicalDevice, wd->Surface, pRequestSurfaceImageFormats, requestSurfaceImageFormatsCount, requestSurfaceColorSpace);
-
-    // Select Present Mode
-    ImGui_ImplVulkan_SelectPresentMode(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, v->SecondaryViewportsInfo.SwapChainImageUsage);
-    vd->WindowOwned = true;
+    bd->ViewportsFormat = ImGui_ImplVulkanH_SelectSurfaceFormat(v->PhysicalDevice, surface, pRequestSurfaceImageFormats, requestSurfaceImageFormatsCount, requestSurfaceColorSpace);
 
     // Create pipeline (shared by all secondary viewports)
     if (bd->PipelineForViewports == VK_NULL_HANDLE)
     {
 #ifdef IMGUI_IMPL_VULKAN_HAS_DYNAMIC_RENDERING
-        if (wd->UseDynamicRendering)
+        if (v->UseDynamicRendering)
         {
             pipeline_info->PipelineRenderingCreateInfo.sType = VK_STRUCTURE_TYPE_PIPELINE_RENDERING_CREATE_INFO;
             pipeline_info->PipelineRenderingCreateInfo.colorAttachmentCount = 1;
-            pipeline_info->PipelineRenderingCreateInfo.pColorAttachmentFormats = &wd->SurfaceFormat.format;
+            pipeline_info->PipelineRenderingCreateInfo.pColorAttachmentFormats = &bd->ViewportsFormat.format;
         }
         else
         {
-            pipeline_info->RenderPass = wd->RenderPass;
+            // Create a reference RenderPass (needed for the Pipeline creation)
+            // Viewports will create their own RenderPass, compatible with this one (same format, different clear option)
+            pipeline_info->RenderPass = ImGui_ImplVulkanH_CreateRenderPass(v->Device, v->Allocator, bd->ViewportsFormat.format, true);
+            pipeline_info->Subpass = 0;
         }
 #endif
         bd->PipelineForViewports = ImGui_ImplVulkan_CreatePipeline(v->Device, v->Allocator, VK_NULL_HANDLE, pipeline_info);
     }
 }
 
+static void ImGui_ImplVulkan_CreateWindow(ImGuiViewport* viewport)
+{
+    ImGui_ImplVulkan_Data* bd = ImGui_ImplVulkan_GetBackendData();
+    ImGui_ImplVulkan_ViewportData* vd = IM_NEW(ImGui_ImplVulkan_ViewportData)();
+    viewport->RendererUserData = vd;
+    ImGui_ImplVulkanH_Window* wd = &vd->Window;
+    ImGui_ImplVulkan_InitInfo* v = &bd->VulkanInitInfo;
+
+    // Create surface
+    ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();
+    VkResult err = (VkResult)platform_io.Platform_CreateVkSurface(viewport, (ImU64)v->Instance, (const void*)v->Allocator, (ImU64*)&wd->Surface);
+    check_vk_result(err);
+
+    // Check for WSI support
+    VkBool32 res;
+    vkGetPhysicalDeviceSurfaceSupportKHR(v->PhysicalDevice, v->QueueFamily, wd->Surface, &res);
+    if (res != VK_TRUE)
+    {
+        IM_ASSERT(0); // Error: no WSI support on physical device
+        return;
+    }
+
+    // Select Present Mode
+    ImGui_ImplVulkan_SelectPresentMode(viewport);
+
+    if (bd->ViewportsFormat.format == VK_FORMAT_UNDEFINED)
+    {
+        ImGui_ImplVulkan_PrepareViewportsRendering(wd->Surface);
+    }
+    wd->SurfaceFormat = bd->ViewportsFormat;
+
+    // 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, v->SecondaryViewportsInfo.SwapChainImageUsage);
+    vd->WindowOwned = true;
+}
+
 static void ImGui_ImplVulkan_DestroyWindow(ImGuiViewport* viewport)
 {
     // The main viewport (owned by the application) will always have RendererUserData == 0 since we didn't create the data for it.