VK_QCOM_tile_shading

Other Extension Metadata

Last Modified Date

2023-10-12

IP Status

No known IP claims.

Interactions and External Dependencies

This extension interacts with VK_KHR_dynamic_rendering
This extension interacts with VK_EXT_transform_feedback
This extension interacts with VK_EXT_debug_marker
This extension interacts with VK_EXT_attachment_feedback_loop_layout
This extension interacts with VK_KHR_dynamic_rendering_local_read
This extension interacts with VK_QCOM_image_processing

Contributors

Jeff Leger, Qualcomm
Matt Netsch, Qualcomm
Srihari Babu Alla, Qualcomm
Matthew Smith, Qualcomm
Kevin Matlage, Qualcomm
Alex Bourd, Qualcomm

This extension exposes tile shading in Vulkan. Many mobile GPUs utilize Tile-Based Deferred Rendering (TBDR) to optimize for power and performance. Conversely, most desktop GPUs use immediate-mode rendering (IM). Adreno ™ GPUs uniquely have the ability to operate in either mode, and when this extension is not enabled, the Adreno driver will select the most optimal mode (TBDR or IM) based on the workload; this feature is called FlexRender ™. When this extension is in use, FlexRender is disabled and the GPU operates exclusively in TBDR wherever possible.

The TBDR mode divides the color and depth/stencil buffer attachments into a regular grid of smaller regions called "tiles". When a render pass instance is submitted for execution on an Adreno GPU, the rendering is split into two phases: a single "visibility pass" followed by multiple "rendering passes" where a separate render pass is issued for each tile in the framebuffer.

The "visibility pass" processes the geometry: identifies which tiles are covered by each primitive, eliminates occluded primitives and unneeded state changes, and performs other tile-specific optimizations. The primitive coverage information collected during the visibility pass is used in the subsequent "rendering pass" for each tile. During the rendering pass for each tile, any primitives that were determined not to cover the current tile are skipped.

This deferred rasterization additionally utilizes a specialized high-bandwidth on-die memory, "tile memory". Tile memory is dramatically more efficient than other device memory. The tile memory temporarily stores the color and other attachments for each tile during rasterization. After each tile is fully rasterized, the resulting tile is typically copied to device memory backing the attachment as specified by the render pass STORE_OP. The per-tile rendering passes occur independently for each tile, with multiple tiles potentially being processed in parallel.

This extension enables applications to leverage the power and performance of tile memory in new ways:

Adds a mechanism for recording dispatches or draws that are guaranteed to be executed per-tile.
Such draws bypass the above-mentioned visibility-based skipping and are guaranteed to be executed for every tile in the rendering pass.
Shaders can declare "tile attachments" variables, providing shader access to color, depth/stencil, and input attachment pixels.
Fragment and compute shaders can read these render pass attachments at any location within the tile. Compute shaders can also write to color attachments at any location within the tile.
Shaders can use new built-in variables that provide the location, size, and apron region of the tile.
A new tile dispatch command automatically scales workgroup sizes and counts to the tile size, given a desired shading rate.
Framebuffer-local dependencies are expanded to tile-sized regions, rather than a single pixel or sample.
A tile shading render pass can also enable tiling "aprons". This is a specialized rendering mode where the GPU renders overlapping tiles that enable specific use-cases.

VkTileShadingRenderPassFlagBitsQCOM

New Bitmasks

VkTileShadingRenderPassFlagsQCOM

New Enum Constants

VK_QCOM_TILE_SHADING_EXTENSION_NAME
VK_QCOM_TILE_SHADING_SPEC_VERSION
Extending VkAccessFlagBits2:
- VK_ACCESS_2_SHADER_TILE_ATTACHMENT_READ_BIT_QCOM
- VK_ACCESS_2_SHADER_TILE_ATTACHMENT_WRITE_BIT_QCOM
Extending VkStructureType:
- VK_STRUCTURE_TYPE_DISPATCH_TILE_INFO_QCOM
- VK_STRUCTURE_TYPE_PER_TILE_BEGIN_INFO_QCOM
- VK_STRUCTURE_TYPE_PER_TILE_END_INFO_QCOM
- VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_TILE_SHADING_FEATURES_QCOM
- VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_TILE_SHADING_PROPERTIES_QCOM
- VK_STRUCTURE_TYPE_RENDER_PASS_TILE_SHADING_CREATE_INFO_QCOM
Extending VkSubpassDescriptionFlagBits:
- VK_SUBPASS_DESCRIPTION_TILE_SHADING_APRON_BIT_QCOM