Backends: Vulkan: Add override for the subpass to reference during VkPipeline creation. (#3579)

This allows for binding the pipeline/sending draw commands
(via `ImGui_ImplVulkan_RenderDrawData`) against any subpass, rather than
being restricted to only the first subpass.

Without this, attempting to bind the pipeline against a subpass other than
the first one results in validation layer errors and, at worst, some drivers
failing if the subpass attachments differ.

backends/imgui_impl_vulkan.cpp

@@ -22,6 +22,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2020-11-11: Vulkan: Added support for specifying which subpass to reference during VkPipeline creation.
 //  2020-09-07: Vulkan: Added VkPipeline parameter to ImGui_ImplVulkan_RenderDrawData (default to one passed to ImGui_ImplVulkan_Init).
 //  2020-05-04: Vulkan: Fixed crash if initial frame has no vertices.
 //  2020-04-26: Vulkan: Fixed edge case where render callbacks wouldn't be called if the ImDrawData didn't have vertices.
@@ -81,6 +82,7 @@ static VkDescriptorSetLayout    g_DescriptorSetLayout = VK_NULL_HANDLE;
 static VkPipelineLayout         g_PipelineLayout = VK_NULL_HANDLE;
 static VkDescriptorSet          g_DescriptorSet = VK_NULL_HANDLE;
 static VkPipeline               g_Pipeline = VK_NULL_HANDLE;
+static uint32_t                 g_Subpass = 0;
 static VkShaderModule           g_ShaderModuleVert;
 static VkShaderModule           g_ShaderModuleFrag;
 
@@ -675,7 +677,7 @@ static void ImGui_ImplVulkan_CreatePipelineLayout(VkDevice device, const VkAlloc
     check_vk_result(err);
 }
 
-static void ImGui_ImplVulkan_CreatePipeline(VkDevice device, const VkAllocationCallbacks* allocator, VkPipelineCache pipelineCache, VkRenderPass renderPass, VkSampleCountFlagBits MSAASamples, VkPipeline* pipeline)
+static void ImGui_ImplVulkan_CreatePipeline(VkDevice device, const VkAllocationCallbacks* allocator, VkPipelineCache pipelineCache, VkRenderPass renderPass, VkSampleCountFlagBits MSAASamples, VkPipeline* pipeline, uint32_t subpass)
 {
     ImGui_ImplVulkan_CreateShaderModules(device, allocator);
 
@@ -775,6 +777,7 @@ static void ImGui_ImplVulkan_CreatePipeline(VkDevice device, const VkAllocationC
     info.pDynamicState = &dynamic_state;
     info.layout = g_PipelineLayout;
     info.renderPass = renderPass;
+    info.subpass = subpass;
     VkResult err = vkCreateGraphicsPipelines(device, pipelineCache, 1, &info, allocator, pipeline);
     check_vk_result(err);
 }
@@ -846,7 +849,7 @@ bool ImGui_ImplVulkan_CreateDeviceObjects()
         check_vk_result(err);
     }
 
-    ImGui_ImplVulkan_CreatePipeline(v->Device, v->Allocator, v->PipelineCache, g_RenderPass, v->MSAASamples, &g_Pipeline);
+    ImGui_ImplVulkan_CreatePipeline(v->Device, v->Allocator, v->PipelineCache, g_RenderPass, v->MSAASamples, &g_Pipeline, g_Subpass);
 
     return true;
 }
@@ -901,6 +904,8 @@ bool    ImGui_ImplVulkan_Init(ImGui_ImplVulkan_InitInfo* info, VkRenderPass rend
 
     g_VulkanInitInfo = *info;
     g_RenderPass = render_pass;
+    g_Subpass = info->Subpass;
+
     ImGui_ImplVulkan_CreateDeviceObjects();
 
     return true;
@@ -1193,7 +1198,7 @@ void ImGui_ImplVulkanH_CreateWindowSwapChain(VkPhysicalDevice physical_device, V
 
         // We do not create a pipeline by default as this is also used by examples' main.cpp,
         // but secondary viewport in multi-viewport mode may want to create one with:
-        //ImGui_ImplVulkan_CreatePipeline(device, allocator, VK_NULL_HANDLE, wd->RenderPass, VK_SAMPLE_COUNT_1_BIT, &wd->Pipeline);
+        //ImGui_ImplVulkan_CreatePipeline(device, allocator, VK_NULL_HANDLE, wd->RenderPass, VK_SAMPLE_COUNT_1_BIT, &wd->Pipeline, g_Subpass);
     }
 
     // Create The Image Views

backends/imgui_impl_vulkan.h

@@ -35,6 +35,7 @@ struct ImGui_ImplVulkan_InitInfo
     VkQueue             Queue;
     VkPipelineCache     PipelineCache;
     VkDescriptorPool    DescriptorPool;
+    uint32_t            Subpass;
     uint32_t            MinImageCount;          // >= 2
     uint32_t            ImageCount;             // >= MinImageCount
     VkSampleCountFlagBits        MSAASamples;   // >= VK_SAMPLE_COUNT_1_BIT

docs/CHANGELOG.txt

@@ -74,6 +74,7 @@ Other Changes:
 - Backends: OpenGL3: Use glGetString(GL_VERSION) query instead of glGetIntegerv(GL_MAJOR_VERSION, ...)
   when the later returns zero (e.g. Desktop GL 2.x). (#3530) [@xndcn]
 - Backends: OpenGL3: Backup and restore GL_PRIMITIVE_RESTART state. (#3544) [@Xipiryon]
+- Backends: Vulkan: Added support for specifying which subpass to reference during VkPipeline creation. (@3579) [@bdero]
 - Backends: OSX: Fix keypad-enter key not working on MacOS. (#3554) [@rokups, @lfnoise]
 - Examples: Apple+Metal: Consolidated/simplified to get closer to other examples. (#3543) [@warrenm]
 - Docs: Split examples/README.txt into docs/BACKENDS.md and docs/EXAMPLES.md improved them.