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Pipeline Dynamic State
| Note |
1. Overview
When creating a graphics VkPipeline object the logical flow for setting state is:
// 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();When the VkPipeline uses dynamic state, some pipeline information can be omitted at creation time and instead set during recording of the command buffer. The new logical flow is:
// 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();2. When to use dynamic state
| Note | Vulkan is a tool, so as with most things, and there is no single answer for this. |
Some implementations might have a performance loss using some certain VkDynamicState state over a static value, but dynamic states might prevent an application from having to create many permutations of pipeline objects which might be a bigger desire for the application.
3. What states are dynamic
The full list of possible dynamic states can be found in VkDynamicState.
The VK_EXT_extended_dynamic_state, VK_EXT_extended_dynamic_state2, VK_EXT_vertex_input_dynamic_state, and VK_EXT_color_write_enable extensions were added with the goal to support applications that need to reduce the number of pipeline state objects they compile and bind.