Backends, Examples: Vulkan: add IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE. use in descriptor pools sizes. (#6642)

Author: ocornut

backends/imgui_impl_vulkan.cpp

@@ -26,6 +26,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2025-01-09: Vulkan: Added IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE to clarify how many image sampler descriptors are expected to be available in descriptor pool. (#6642)
 //  2025-01-06: Vulkan: Added more ImGui_ImplVulkanH_XXXX helper functions to simplify our examples.
 //  2024-12-11: Vulkan: Fixed setting VkSwapchainCreateInfoKHR::preTransform for platforms not supporting VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR. (#8222)
 //  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)
@@ -1022,8 +1023,9 @@ bool ImGui_ImplVulkan_CreateDeviceObjects()
         check_vk_result(err);
     }
 
-    if (v->DescriptorPoolSize)
+    if (v->DescriptorPoolSize != 0)
     {
+        IM_ASSERT(v->DescriptorPoolSize > IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE);
         VkDescriptorPoolSize pool_size = { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, v->DescriptorPoolSize };
         VkDescriptorPoolCreateInfo pool_info = {};
         pool_info.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_POOL_CREATE_INFO;

backends/imgui_impl_vulkan.h

@@ -61,14 +61,16 @@
 #define IMGUI_IMPL_VULKAN_HAS_DYNAMIC_RENDERING
 #endif
 
+// 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. Use this value + number of desired calls to ImGui_ImplVulkan_AddTexture().
+#define IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE   (1)     // Minimum per atlas
+
 // Initialization data, for ImGui_ImplVulkan_Init()
 // [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

docs/CHANGELOG.txt

@@ -79,6 +79,10 @@ Other changes:
   platforms not supporting VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR. (#8222) [@Zer0xFF]
 - Backends: Vulkan: Added a few more ImGui_ImplVulkanH_XXX helper functions
   primarily for the purpose of making our examples simpler.
+- Backends: Vulkan: Added IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE to clarify
+  how many image sampler descriptors are expected to be available in the provided
+  descriptor pool. Current backend needs 1 but it is expected that by end of Q1 2025
+  this number will grow (will staying a very small number). (#6642)
 - Backends: DX11: Expose vertex constant buffer in ImGui_ImplDX11_RenderState.
   Reset projection matrix in ImDrawCallback_ResetRenderState handlers. (#6969, #5834, #7468, #3590)
 - Backends: DX10: Expose ImGui_ImplDX10_RenderState for completeness. (#6969, #5834, #7468, #3590)

examples/example_glfw_vulkan/main.cpp

@@ -189,17 +189,18 @@ static void SetupVulkan(ImVector<const char*> instance_extensions)
     }
 
     // Create Descriptor Pool
-    // The example only requires a single combined image sampler descriptor for the font image and only uses one descriptor set (for that)
-    // If you wish to load e.g. additional textures you may need to alter pools sizes.
+    // If you wish to load e.g. additional textures you may need to alter pools sizes and maxSets.
     {
         VkDescriptorPoolSize pool_sizes[] =
         {
-            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, 1 },
+            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE },
         };
         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 = 1;
+        pool_info.maxSets = 0;
+        for (VkDescriptorPoolSize& pool_size : pool_sizes)
+            pool_info.maxSets += pool_size.descriptorCount;
         pool_info.poolSizeCount = (uint32_t)IM_ARRAYSIZE(pool_sizes);
         pool_info.pPoolSizes = pool_sizes;
         err = vkCreateDescriptorPool(g_Device, &pool_info, g_Allocator, &g_DescriptorPool);

examples/example_sdl2_vulkan/main.cpp

@@ -177,17 +177,18 @@ static void SetupVulkan(ImVector<const char*> instance_extensions)
     }
 
     // Create Descriptor Pool
-    // The example only requires a single combined image sampler descriptor for the font image and only uses one descriptor set (for that)
-    // If you wish to load e.g. additional textures you may need to alter pools sizes.
+    // If you wish to load e.g. additional textures you may need to alter pools sizes and maxSets.
     {
         VkDescriptorPoolSize pool_sizes[] =
         {
-            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, 1 },
+            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE },
         };
         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 = 1;
+        pool_info.maxSets = 0;
+        for (VkDescriptorPoolSize& pool_size : pool_sizes)
+            pool_info.maxSets += pool_size.descriptorCount;
         pool_info.poolSizeCount = (uint32_t)IM_ARRAYSIZE(pool_sizes);
         pool_info.pPoolSizes = pool_sizes;
         err = vkCreateDescriptorPool(g_Device, &pool_info, g_Allocator, &g_DescriptorPool);

examples/example_sdl3_vulkan/main.cpp

@@ -182,17 +182,18 @@ static void SetupVulkan(ImVector<const char*> instance_extensions)
     }
 
     // Create Descriptor Pool
-    // The example only requires a single combined image sampler descriptor for the font image and only uses one descriptor set (for that)
-    // If you wish to load e.g. additional textures you may need to alter pools sizes.
+    // If you wish to load e.g. additional textures you may need to alter pools sizes and maxSets.
     {
         VkDescriptorPoolSize pool_sizes[] =
         {
-            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, 1 },
+            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE },
         };
         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 = 1;
+        pool_info.maxSets = 0;
+        for (VkDescriptorPoolSize& pool_size : pool_sizes)
+            pool_info.maxSets += pool_size.descriptorCount;
         pool_info.poolSizeCount = (uint32_t)IM_ARRAYSIZE(pool_sizes);
         pool_info.pPoolSizes = pool_sizes;
         err = vkCreateDescriptorPool(g_Device, &pool_info, g_Allocator, &g_DescriptorPool);

examples/example_win32_vulkan/main.cpp

@@ -178,17 +178,18 @@ static void SetupVulkan(ImVector<const char*> instance_extensions)
     }
 
     // Create Descriptor Pool
-    // The example only requires a single combined image sampler descriptor for the font image and only uses one descriptor set (for that)
-    // If you wish to load e.g. additional textures you may need to alter pools sizes.
+    // If you wish to load e.g. additional textures you may need to alter pools sizes and maxSets.
     {
         VkDescriptorPoolSize pool_sizes[] =
         {
-            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, 1 },
+            { VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER, IMGUI_IMPL_VULKAN_MINIMUM_IMAGE_SAMPLER_POOL_SIZE },
         };
         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 = 1;
+        pool_info.maxSets = 0;
+        for (VkDescriptorPoolSize& pool_size : pool_sizes)
+            pool_info.maxSets += pool_size.descriptorCount;
         pool_info.poolSizeCount = (uint32_t)IM_ARRAYSIZE(pool_sizes);
         pool_info.pPoolSizes = pool_sizes;
         err = vkCreateDescriptorPool(g_Device, &pool_info, g_Allocator, &g_DescriptorPool);