//// - Copyright (c) 2023, Mobica Limited - - SPDX-License-Identifier: Apache-2.0 - - Licensed under the Apache License, Version 2.0 the "License"; - you may not use this file except in compliance with the License. - You may obtain a copy of the License at - - http://www.apache.org/licenses/LICENSE-2.0 - - Unless required by applicable law or agreed to in writing, software - distributed under the License is distributed on an "AS IS" BASIS, - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - See the License for the specific language governing permissions and - limitations under the License. - //// = Patch control point ifdef::site-gen-antora[] TIP: The source for this sample can be found in the https://github.com/KhronosGroup/Vulkan-Samples/tree/main/samples/extensions/patch_control_points[Khronos Vulkan samples github repository]. endif::[] image::./images/patch_control_point_screenshot.png[Sample] == Overview This sample demonstrates how to use `VK_EXT_extended_dynamic_state2` extension, which eliminates the need to create multiple pipelines in case of specific different parameters. This extension changes how *Patch Control Points* are managed. Instead of static description during pipeline creation, this extension allows developers to change the parameter by using a function before every draw. Below is a comparison of common Vulkan static and dynamic setting of patch control points in the tessellation. |=== | Static/Non-dynamic | Dynamic State 2 | dynamic_state = {VK_DYNAMIC_STATE_VIEWPORT, + VK_DYNAMIC_STATE_SCISSOR} | dynamic_state = {VK_DYNAMIC_STATE_VIEWPORT, + VK_DYNAMIC_STATE_SCISSOR, + *VK_DYNAMIC_STATE_PATCH_CONTROL_POINTS_EXT*} | VkPipelineTessellationStateCreateInfo tessellation_state{} + tessellation_state.sType = VK_STRUCTURE_TYPE_PIPELINE_TESSELLATION_STATE_CREATE_INFO + *tessellation_state.patchControlPoints = patchControlPoints* + ... + vkCreateGraphicsPipelines(pipeline) | vkCreateGraphicsPipelines(pipeline) | draw(model, pipeline) | *vkCmdSetPatchControlPointsEXT(commandBuffer, patchControlPoints)* + draw(model, pipeline) |=== More details are provided in the sections that follow. == Pipelines In the static approach to pipeline creation patch control points have to be defined while creating the pipeline. This is illustrated in a static/non-dynamic pipeline creation. [,C++] ---- VkPipelineInputAssemblyStateCreateInfo input_assembly_state = vkb::initializers::pipeline_input_assembly_state_create_info( VK_PRIMITIVE_TOPOLOGY_PATCH_LIST, 0, VK_FALSE); VkPipelineTessellationStateCreateInfo tessellation_state = vkb::initializers::pipeline_tessellation_state_create_info(3); std::vector dynamic_state_enables = { VK_DYNAMIC_STATE_VIEWPORT, VK_DYNAMIC_STATE_SCISSOR }; VkPipelineDynamicStateCreateInfo dynamic_state = vkb::initializers::pipeline_dynamic_state_create_info( dynamic_state_enables.data(), static_cast(dynamic_state_enables.size()), 0); VkGraphicsPipelineCreateInfo graphics_create{VK_STRUCTURE_TYPE_GRAPHICS_PIPELINE_CREATE_INFO}; graphics_create.pInputAssemblyState = &input_assembly_state; graphics_create.pDynamicState = &dynamic_state; graphics_create.pTessellationState = &tessellation_state; graphics_create.layout = pipeline_layouts.statically_tessellation; ... VK_CHECK(vkCreateGraphicsPipelines(get_device().get_handle(), pipeline_cache, 1, &graphics_create, VK_NULL_HANDLE, &pipeline.statically_tessellation)); ---- In the approach if developer would like to change the patch control points number, then for each different number a new pipeline would be required. However, with `VK_EXT_extended_dynamic_state2` the number of pipelines can be reduced by the possibility to change parameter Patch Control Points by calling `vkCmdSetPatchControlPointsEXT` before calling the `draw_model` method. With the usage of above function we can reduce the number of pipelines. Required dynamic states must be enabled and passed to the `VkGraphicsPipelineCreateInfo` structure. By setting `VK_PRIMITIVE_TOPOLOGY_PATCH_LIST` in the `VkPipelineInputAssemblyStateCreateInfo` structure, the pipeline can use the `patch control points` functionality. [,C+] ---- VkPipelineInputAssemblyStateCreateInfo input_assembly_state = vkb::initializers::pipeline_input_assembly_state_create_info( VK_PRIMITIVE_TOPOLOGY_PATCH_LIST, 0, VK_FALSE); std::vector dynamic_state_enables = { VK_DYNAMIC_STATE_VIEWPORT, VK_DYNAMIC_STATE_SCISSOR, VK_DYNAMIC_STATE_PATCH_CONTROL_POINTS_EXT, }; VkPipelineDynamicStateCreateInfo dynamic_state = vkb::initializers::pipeline_dynamic_state_create_info( dynamic_state_enables.data(), static_cast(dynamic_state_enables.size()), 0); VkGraphicsPipelineCreateInfo graphics_create{VK_STRUCTURE_TYPE_GRAPHICS_PIPELINE_CREATE_INFO}; graphics_create.pInputAssemblyState = &input_assembly_state; graphics_create.pDynamicState = &dynamic_state; graphics_create.layout = pipeline_layouts.dynamically_tessellation; ... VK_CHECK(vkCreateGraphicsPipelines(get_device().get_handle(), pipeline_cache, 1, &graphics_create, VK_NULL_HANDLE, &pipeline.dynamically_tessellation)); ---- And now, thanks to `VK_EXT_extended_dynamic_state2`, we can change parameters before each corresponding draw call. [,C++] ---- VK_CHECK(vkBeginCommandBuffer(draw_cmd_buffer, &command_begin)); ... /* Binding dynamically_tessellation pipeline and descriptor sets */ vkCmdBindDescriptorSets(draw_cmd_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline_layouts.dynamically_tessellation, 0, 1, &descriptor_sets.dynamically_tessellation, 0, nullptr); vkCmdBindPipeline(draw_cmd_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline.dynamically_tessellation); /* Set patch control points value */ vkCmdSetPatchControlPointsEXT(draw_cmd_buffer, patch_control_points_triangle); /* Drawing scene with objects using tessellation feature */ draw_model(model, draw_cmd_buffer); ... VK_CHECK(vkEndCommandBuffer(draw_cmd_buffer)); ---- == Enabling the Extension The extended dynamic state 2 API requires Vulkan 1.0 and the appropriate headers / SDK is required. This extension has been https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VK_EXT_extended_dynamic_state2.html#_promotion_to_vulkan_1_3[partially] promoted to Vulkan 1.3. The device extension is provided by `VK_EXT_EXTENDED_DYNAMIC_STATE_2_EXTENSION_NAME`. It also requires `VK_KHR_GET_PHYSICAL_DEVICE_PROPERTIES_2_EXTENSION_NAME` instance extension to be enabled. [,C++] ---- add_instance_extension(VK_KHR_GET_PHYSICAL_DEVICE_PROPERTIES_2_EXTENSION_NAME); add_device_extension(VK_EXT_EXTENDED_DYNAMIC_STATE_2_EXTENSION_NAME); ---- If the https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkPhysicalDeviceExtendedDynamicState2FeaturesEXT.html[`VkPhysicalDeviceExtendedDynamicState2FeaturesEXT`] structure is included in the pNext chain of the `VkPhysicalDeviceFeatures2` structure passed to vkGetPhysicalDeviceFeatures2, it is filled in to indicate whether each corresponding feature is supported. `VkPhysicalDeviceExtendedDynamicState2FeaturesEXT` can also be used in the pNext chain of `VkDeviceCreateInfo` to selectively enable these features.