mirror of https://gitlab.freedesktop.org/mesa/mesa
112 lines
4.2 KiB
ReStructuredText
112 lines
4.2 KiB
ReStructuredText
Render Passes
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=============
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The Vulkan runtime code in Mesa provides several helpful utilities to make
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managing render passes easier.
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:ext:`VK_KHR_create_renderpass2`
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--------------------------------
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It is strongly recommended that drivers implement
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:ext:`VK_KHR_create_renderpass2` directly and not bother implementing the
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old Vulkan 1.0 entrypoints. If a driver does not implement them, the
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following will be implemented in common code in terms of their
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:ext:`VK_KHR_create_renderpass2` counterparts:
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- :c:func:`vkCreateRenderPass`
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- :c:func:`vkCmdBeginRenderPass`
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- :c:func:`vkCmdNextSubpass`
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- :c:func:`vkCmdEndRenderPass`
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Common VkRenderPass implementation
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----------------------------------
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The Vulkan runtime code in Mesa provides a common implementation of
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:c:type:`VkRenderPass` called :c:struct:`vk_render_pass` which drivers
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can optionally use. Unlike most Vulkan runtime structs, it's not really
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designed to be used as a base for a driver-specific struct. It does,
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however, contain all the information passed to
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:c:func:`vkCreateRenderPass2` so it can be used in a driver so long as
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that driver doesn't need to do any additional compilation at
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:c:func:`vkCreateRenderPass2` time. If a driver chooses to use
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:c:struct:`vk_render_pass`, the Vulkan runtime provides implementations
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of :c:func:`vkCreateRenderPass2` and :c:func:`vkDestroyRenderPass`.
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:ext:`VK_KHR_dynamic_rendering`
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-------------------------------
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For drivers which don't need to do subpass combining, it is recommended
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that they skip implementing render passes entirely and implement
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:ext:`VK_KHR_dynamic_rendering` instead. If they choose to do so, the runtime
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will provide the following, implemented in terms of
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:c:func:`vkCmdBeginRendering` and :c:func:`vkCmdEndRendering`:
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- :c:func:`vkCmdBeginRenderPass2`
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- :c:func:`vkCmdNextSubpass2`
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- :c:func:`vkCmdEndRenderPass2`
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We also provide a no-op implementation of
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:c:func:`vkGetRenderAreaGranularity` which returns a render area
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granularity of 1x1.
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Drivers which wish to use the common render pass implementation in this way
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**must** also support a Mesa-specific pseudo-extension which optionally
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provides an initial image layout for each attachment at
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:c:func:`vkCmdBeginRendering` time. This is required for us to combine
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render pass clears with layout transitions, often from
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:c:enum:`VK_IMAGE_LAYOUT_UNDEFINED`. On at least Intel and AMD,
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combining these transitions with clears is important for performance.
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.. c:autostruct:: VkRenderingAttachmentInitialLayoutInfoMESA
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:file: src/vulkan/runtime/vk_render_pass.h
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:members:
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Because render passes and subpass indices are also passed into
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:c:func:`vkCmdCreateGraphicsPipelines` and
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:c:func:`vkCmdExecuteCommands` which we can't implement on the driver's
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behalf, we provide a couple of helpers for getting the render pass
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information in terms of the relevant :ext:`VK_KHR_dynamic_rendering`:
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.. c:autofunction:: vk_get_pipeline_rendering_create_info
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:file: src/vulkan/runtime/vk_render_pass.h
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.. c:autofunction:: vk_get_command_buffer_inheritance_rendering_info
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:file: src/vulkan/runtime/vk_render_pass.h
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Apart from handling layout transitions, the common render pass
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implementation mostly ignores input attachments. It is expected that the
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driver call :c:func:`nir_lower_input_attachments` to turn them into
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texturing operations. The driver **must** support texturing from an input
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attachment at the same time as rendering to it in order to support Vulkan
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subpass self-dependencies. ``VK_EXT_attachment_feedback_loop_layout`` provides
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information on when these self dependencies are present.
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vk_render_pass reference
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------------------------
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The following is a reference for the :c:struct:`vk_render_pass` structure
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and its substructures.
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.. c:autostruct:: vk_render_pass
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:file: src/vulkan/runtime/vk_render_pass.h
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:members:
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.. c:autostruct:: vk_render_pass_attachment
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:file: src/vulkan/runtime/vk_render_pass.h
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:members:
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.. c:autostruct:: vk_subpass
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:file: src/vulkan/runtime/vk_render_pass.h
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:members:
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.. c:autostruct:: vk_subpass_attachment
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:file: src/vulkan/runtime/vk_render_pass.h
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:members:
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.. c:autostruct:: vk_subpass_dependency
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:file: src/vulkan/runtime/vk_render_pass.h
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:members:
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