动态管线状态

dynamic state称为动态管线状态。

提示

更详细内容请阅读Vulkan Spec的内容。

概述

创建一个图形 VkPipeline对象时，设置 state 的流程为：

// Using viewport state as an example
VkViewport viewport = {0.0, 0.0, 32.0, 32.0, 0.0, 1.0};

// Set value of state
VkPipelineViewportStateCreateInfo viewportStateCreateInfo;
viewportStateCreateInfo.pViewports = &viewport;
viewportStateCreateInfo.viewportCount = 1;

// Create the pipeline with the state value set
VkGraphicsPipelineCreateInfo pipelineCreateInfo;
pipelineCreateInfo.pViewportState = &viewportStateCreateInfo;
vkCreateGraphicsPipelines(pipelineCreateInfo, &pipeline);

vkBeginCommandBuffer();
// Select the pipeline and draw with the state's static value
vkCmdBindPipeline(pipeline);
vkCmdDraw();
vkEndCommandBuffer();

VkPipeline使用 dynamic state 的场景是，一些信息可以在创建管线时省略，然后在记录命令缓冲区的时候设置，流程为：

// Using viewport state as an example
VkViewport viewport = {0.0, 0.0, 32.0, 32.0, 0.0, 1.0};
VkDynamicState dynamicState = VK_DYNAMIC_STATE_VIEWPORT;

// not used now
VkPipelineViewportStateCreateInfo viewportStateCreateInfo;
viewportStateCreateInfo.pViewports = nullptr;
// still need to say how many viewports will be used here
viewportStateCreateInfo.viewportCount = 1;

// Set the state as being dynamic
VkPipelineDynamicStateCreateInfo dynamicStateCreateInfo;
dynamicStateCreateInfo.dynamicStateCount = 1;
dynamicStateCreateInfo.pDynamicStates = &dynamicState;

// Create the pipeline with state value not known
VkGraphicsPipelineCreateInfo pipelineCreateInfo;
pipelineCreateInfo.pViewportState = &viewportStateCreateInfo;
pipelineCreateInfo.pDynamicState = &dynamicStateCreateInfo;
vkCreateGraphicsPipelines(pipelineCreateInfo, &pipeline);

vkBeginCommandBuffer();
vkCmdBindPipeline(pipeline);
// Set the state for the pipeline at recording time
vkCmdSetViewport(viewport);
vkCmdDraw();
viewport.height = 64.0;
// set a new state value between draws
vkCmdSetViewport(viewport);
vkCmdDraw();
vkEndCommandBuffer();

什么时候使用dynamic state

提示

Vulkan 是一种工具，与大多数事物一样，这个问题没有绝对的答案。

某些驱动实现使用VkDynamicState相比静态状态可能有性能损失，但使用动态状态，可以让应用程序创建更少的管线，对于会变化的管线状态，应用程序可能更多的会使用dynamic state。

哪些状态是动态的

动态状态的完整列表可在 Vulkan Spec VkDynamicState 中找到。

添加VK_EXT_extended_dynamic_state 、VK_EXT_extended_dynamic_state2 、VK_EXT_extended_dynamic_state3 、 VK_EXT_vertex_input_dynamic_state、VK_EXT_attachment_feedback_loop_dynamic_state和VK_EXT_color_write_enable 扩展的目的，是让应用程序减少编译和绑定管线状态的数量。