Backends: Vulkan: Make descriptor pool optional (#8172, #4867)

Comments/amends by ocornut

backends/imgui_impl_vulkan.cpp

@@ -26,6 +26,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2024-11-27: Vulkan: Make user-provided descriptor pool optional. As a convenience, when setting init_info->DescriptorPoolSize the backend will create one itself. (#8172, #4867)
 //  2024-10-07: Vulkan: Changed default texture sampler to Clamp instead of Repeat/Wrap.
 //  2024-10-07: Vulkan: Expose selected render state in ImGui_ImplVulkan_RenderState, which you can access in 'void* platform_io.Renderer_RenderState' during draw callbacks.
 //  2024-10-07: Vulkan: Compiling with '#define ImTextureID=ImU64' is unnecessary now that dear imgui defaults ImTextureID to u64 instead of void*.
@@ -131,6 +132,7 @@ static bool g_FunctionsLoaded = true;
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkCmdSetViewport) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkCreateBuffer) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkCreateCommandPool) \
+    IMGUI_VULKAN_FUNC_MAP_MACRO(vkCreateDescriptorPool) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkCreateDescriptorSetLayout) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkCreateFence) \
     IMGUI_VULKAN_FUNC_MAP_MACRO(vkCreateFramebuffer) \
@@ -221,6 +223,7 @@ struct ImGui_ImplVulkan_Data
     VkPipeline                  Pipeline;
     VkShaderModule              ShaderModuleVert;
     VkShaderModule              ShaderModuleFrag;
+    VkDescriptorPool            DescriptorPool;
 
     // Font data
     VkSampler                   FontSampler;
@@ -1010,6 +1013,20 @@ bool ImGui_ImplVulkan_CreateDeviceObjects()
         check_vk_result(err);
     }
 
+    if (v->DescriptorPoolSize)
+    {
+        VkDescriptorPoolSize pool_size = { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, v->DescriptorPoolSize };
+        VkDescriptorPoolCreateInfo pool_info = {};
+        pool_info.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_POOL_CREATE_INFO;
+        pool_info.flags = VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT;
+        pool_info.maxSets = v->DescriptorPoolSize;
+        pool_info.poolSizeCount = 1;
+        pool_info.pPoolSizes = &pool_size;
+
+        err = vkCreateDescriptorPool(v->Device, &pool_info, v->Allocator, &bd->DescriptorPool);
+        check_vk_result(err);
+    }
+
     if (!bd->PipelineLayout)
     {
         // Constants: we are using 'vec2 offset' and 'vec2 scale' instead of a full 3d projection matrix
@@ -1048,6 +1065,7 @@ 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->DescriptorPool)       { vkDestroyDescriptorPool(v->Device, bd->DescriptorPool, v->Allocator); bd->DescriptorPool = VK_NULL_HANDLE; }
 }
 
 bool    ImGui_ImplVulkan_LoadFunctions(PFN_vkVoidFunction(*loader_func)(const char* function_name, void* user_data), void* user_data)
@@ -1110,7 +1128,10 @@ bool    ImGui_ImplVulkan_Init(ImGui_ImplVulkan_InitInfo* info)
     IM_ASSERT(info->PhysicalDevice != VK_NULL_HANDLE);
     IM_ASSERT(info->Device != VK_NULL_HANDLE);
     IM_ASSERT(info->Queue != VK_NULL_HANDLE);
-    IM_ASSERT(info->DescriptorPool != VK_NULL_HANDLE);
+    if (info->DescriptorPool != VK_NULL_HANDLE) // Either DescriptorPool or DescriptorPoolSize must be set, not both!
+        IM_ASSERT(info->DescriptorPoolSize == 0);
+    else
+        IM_ASSERT(info->DescriptorPoolSize > 0);
     IM_ASSERT(info->MinImageCount >= 2);
     IM_ASSERT(info->ImageCount >= info->MinImageCount);
     if (info->UseDynamicRendering == false)
@@ -1159,19 +1180,20 @@ void ImGui_ImplVulkan_SetMinImageCount(uint32_t min_image_count)
     bd->VulkanInitInfo.MinImageCount = min_image_count;
 }
 
-// Register a texture
+// Register a texture by creating a descriptor
 // FIXME: This is experimental in the sense that we are unsure how to best design/tackle this problem, please post to https://github.com/ocornut/imgui/pull/914 if you have suggestions.
 VkDescriptorSet ImGui_ImplVulkan_AddTexture(VkSampler sampler, VkImageView image_view, VkImageLayout image_layout)
 {
     ImGui_ImplVulkan_Data* bd = ImGui_ImplVulkan_GetBackendData();
     ImGui_ImplVulkan_InitInfo* v = &bd->VulkanInitInfo;
+    VkDescriptorPool pool = bd->DescriptorPool ? bd->DescriptorPool : v->DescriptorPool;
 
     // Create Descriptor Set:
     VkDescriptorSet descriptor_set;
     {
         VkDescriptorSetAllocateInfo alloc_info = {};
         alloc_info.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_ALLOCATE_INFO;
-        alloc_info.descriptorPool = v->DescriptorPool;
+        alloc_info.descriptorPool = pool;
         alloc_info.descriptorSetCount = 1;
         alloc_info.pSetLayouts = &bd->DescriptorSetLayout;
         VkResult err = vkAllocateDescriptorSets(v->Device, &alloc_info, &descriptor_set);
@@ -1199,7 +1221,8 @@ void ImGui_ImplVulkan_RemoveTexture(VkDescriptorSet descriptor_set)
 {
     ImGui_ImplVulkan_Data* bd = ImGui_ImplVulkan_GetBackendData();
     ImGui_ImplVulkan_InitInfo* v = &bd->VulkanInitInfo;
-    vkFreeDescriptorSets(v->Device, v->DescriptorPool, 1, &descriptor_set);
+    VkDescriptorPool pool = bd->DescriptorPool ? bd->DescriptorPool : v->DescriptorPool;
+    vkFreeDescriptorSets(v->Device, pool, 1, &descriptor_set);
 }
 
 void ImGui_ImplVulkan_DestroyFrameRenderBuffers(VkDevice device, ImGui_ImplVulkan_FrameRenderBuffers* buffers, const VkAllocationCallbacks* allocator)

backends/imgui_impl_vulkan.h

@@ -62,10 +62,15 @@
 #endif
 
 // Initialization data, for ImGui_ImplVulkan_Init()
-// - VkDescriptorPool should be created with VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT,
-//   and must contain a pool size large enough to hold an ImGui VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER descriptor.
-// - When using dynamic rendering, set UseDynamicRendering=true and fill PipelineRenderingCreateInfo structure.
 // [Please zero-clear before use!]
+// - About descriptor pool:
+//   - A VkDescriptorPool should be created with VK_DESCRIPTOR_POOL_CREATE_FREE_DESCRIPTOR_SET_BIT,
+//     and must contain a pool size large enough to hold a small number of VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER descriptors.
+//   - As an convenience, by setting DescriptorPoolSize > 0 the backend will create one for you.
+//   - Current version of the backend use 1 descriptor for the font atlas + as many as additional calls done to ImGui_ImplVulkan_AddTexture().
+//   - It is expected that as early as Q1 2025 the backend will use a few more descriptors, so aim at 10 + number of desierd calls to ImGui_ImplVulkan_AddTexture().
+// - About dynamic rendering:
+//   - When using dynamic rendering, set UseDynamicRendering=true and fill PipelineRenderingCreateInfo structure.
 struct ImGui_ImplVulkan_InitInfo
 {
     VkInstance                      Instance;
@@ -73,7 +78,7 @@ struct ImGui_ImplVulkan_InitInfo
     VkDevice                        Device;
     uint32_t                        QueueFamily;
     VkQueue                         Queue;
-    VkDescriptorPool                DescriptorPool;               // See requirements in note above
+    VkDescriptorPool                DescriptorPool;               // See requirements in note above; ignored if using DescriptorPoolSize > 0
     VkRenderPass                    RenderPass;                   // Ignored if using dynamic rendering
     uint32_t                        MinImageCount;                // >= 2
     uint32_t                        ImageCount;                   // >= MinImageCount
@@ -83,6 +88,9 @@ struct ImGui_ImplVulkan_InitInfo
     VkPipelineCache                 PipelineCache;
     uint32_t                        Subpass;
 
+    // (Optional) Set to create internal descriptor pool instead of using DescriptorPool
+    uint32_t                        DescriptorPoolSize;
+
     // (Optional) Dynamic Rendering
     // Need to explicitly enable VK_KHR_dynamic_rendering extension to use this, even for Vulkan 1.3.
     bool                            UseDynamicRendering;

docs/CHANGELOG.txt

@@ -59,6 +59,9 @@ Other changes:
 - Tools: binary_to_compressed_c: added -u8/-u32/-base85 export options.
 - Demo: example tree used by Property Editor & Selection demos properly freed
   on application closure. (#8158) [@Legulysse]
+- Backends: Vulkan: Make user-provided descriptor pool optional. As a convenience,
+  when setting init_info->DescriptorPoolSize then the backend will create and manage
+  one itself. (#8172, #4867) [@zeux]
 - Examples: Win32+DX12: Using a basic free-list allocator to manage multiple
   SRV descriptors.