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* Update release number to 91.
Public Issues:
* Update Ubuntu subsystem build instructions in `BUILD.adoc` (public pull
request 624).
* Delete the `VK_KHR_mir_surface` extension from the Specification and
XML, due to EOL of the only driver known to have supported it, and
near-EOL of Mir itself (public issue 814).
* Fix options for some figures that were using old ones (public pull
request 841).
* Fix various accidentally repeated words (public pull request 843).
* Use `time.process_time()`, introduced in Python 3.3, in the scripts
instead of `time.clock()`, which will be removed in Python 3.8 (public
pull request 844).
Internal Issues:
* Update valid usage statements for
`VK_ANDROID_external_memory_android_hardware_buffer` in
slink:VkMemoryAllocateInfo,
slink:VkImportAndroidHardwareBufferInfoANDROID, and
flink:vkGetAndroidHardwareBufferPropertiesANDROID to actually be
verifiable (internal issue 1419).
* Update valid usage statements for
`VK_ANDROID_external_memory_android_hardware_buffer` in
slink:VkMemoryAllocateInfo, slink:VkImageCreateInfo, and
slink:VkImageViewCreateInfo to move valid usage statements in
doubly-nested bullet points up one level, accomodating limitations of
the valid usage extraction script that creates `validusage.json`
(internal issue 1434).
* Fix typo etext:VK_ACCESS_SHADING_RATE_IMAGE_BIT_NV to the correct
ename:VK_ACCESS_SHADING_RATE_IMAGE_READ_BIT_NV.
* Add missing etext:VK_STRUCTURE_TYPE_* tokens to appendices for
extensions missing them.
New Extensions:
* `VK_AMD_memory_overallocation_behavior`
* `VK_NV_ray_tracing`, replacing `VK_NVX_raytracing`
104 lines
3.6 KiB
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104 lines
3.6 KiB
Plaintext
// This section is included inside the Shaders chapter (shaders.txt)
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[[shaders-raytracing-shaders]]
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[[shaders-ray-generation]]
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== Ray Generation Shaders
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A ray generation shader is similar to a compute shader.
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Its main purpose is to execute ray tracing queries using code:OpTraceNV
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instructions and process the results.
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[[shaders-ray-generation-execution]]
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=== Ray Generation Shader Execution
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One ray generation shader is executed per ray tracing dispatch.
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Its location in the shader binding table (see <<shader-binding-table,Shader
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Binding Table>> for details) is passed directly into fname:vkCmdTraceRaysNV
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using the pname:raygenShaderBindingTableBuffer and
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pname:raygenShaderBindingOffset parameters.
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[[shaders-intersection]]
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== Intersection Shaders
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Intersection shaders enable the implementation of arbitrary, application
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defined geometric primitives.
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An intersection shader for a primitive is executed whenever its axis-aligned
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bounding box is hit by a ray.
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A built-in intersection shader for triangle primitives that is used
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automatically whenever geometry of type ename:VK_GEOMETRY_TYPE_TRIANGLES_NV
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is specified.
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Like other ray tracing shader domains, an intersection shader operates on a
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single ray at a time.
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It also operates on a single primitive at a time.
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It is therefore the purpose of an intersection shader to compute the
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ray-primitive intersections and report them.
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To report an intersection, the shader calls the code:OpReportIntersectionNV
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instruction.
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An intersection shader communicates with any hit and closest shaders by
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generating attribute values that they can read.
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Intersection shaders cannot read or modify the ray payload.
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[[shaders-intersection-execution]]
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=== Intersection Shader Execution
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[[shaders-any-hit]]
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== Any Hit Shaders
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The any hit shader is executed after the intersection shader reports an
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intersection that lies within the current [tmin,tmax] of the ray.
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The main use of any hit shaders is to programmatically decide whether or not
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an intersection should be accepted.
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The intersection will be accepted unless the shader calls the
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code:OpIgnoreIntersectionNV instruction.
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[[shaders-any-hit-execution]]
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=== Any Hit Shader Execution
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The order in which intersections are found along a ray, and therefore the
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order in which any hit shaders are executed, is unspecified.
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The any hit shader of the closest hit is guaranteed to be executed at some
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point during traversal, unless the ray is forcibly terminated.
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[[shaders-closest-hit]]
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== Closest Hit Shaders
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Closest hit shaders have read-only access to the attributes generated by the
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corresponding intersection shader, and may: read or modify the ray payload.
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They also have access to a number of system-generated values.
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Closest hit shaders may call code:OpTraceNV to recursively trace rays.
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[[shaders-closest-hit-execution]]
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=== Closest Hit Shader Execution
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Exactly one closest hit shader is executed when traversal is finished and an
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intersection has been found and accepted.
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[[shaders-miss]]
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== Miss Shaders
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Miss shaders can access the ray payload and can trace new rays through the
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code:OpTraceNV instruction, but cannot access attributes since they are not
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associated with an intersection.
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[[shaders-miss-execution]]
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=== Miss Shader Execution
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A miss shader is executed instead of a closest hit shader if no intersection
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was found during traversal.
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[[shaders-callable]]
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== Callable Shaders
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Callable shaders may: access a callable payload that works similarly to ray
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payloads to do subroutine work.
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[[shaders-callable-execution]]
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=== Callable Shader Execution
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A callable shader is executed by calling code:OpExecuteCallableNV from an
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allowed shader stage.
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