1  // This section is included inside the Shaders chapter (shaders.txt)
  2  
  3  [[shaders-raytracing-shaders]]
  4  [[shaders-ray-generation]]
  5  == Ray Generation Shaders
  6  
  7  A ray generation shader is similar to a compute shader.
  8  Its main purpose is to execute ray tracing queries using code:OpTraceNV
  9  instructions and process the results.
 10  
 11  [[shaders-ray-generation-execution]]
 12  === Ray Generation Shader Execution
 13  
 14  One ray generation shader is executed per ray tracing dispatch.
 15  Its location in the shader binding table (see <<shader-binding-table,Shader
 16  Binding Table>> for details) is passed directly into fname:vkCmdTraceRaysNV
 17  using the pname:raygenShaderBindingTableBuffer and
 18  pname:raygenShaderBindingOffset parameters.
 19  
 20  [[shaders-intersection]]
 21  == Intersection Shaders
 22  
 23  Intersection shaders enable the implementation of arbitrary, application
 24  defined geometric primitives.
 25  An intersection shader for a primitive is executed whenever its axis-aligned
 26  bounding box is hit by a ray.
 27  
 28  A built-in intersection shader for triangle primitives that is used
 29  automatically whenever geometry of type ename:VK_GEOMETRY_TYPE_TRIANGLES_NV
 30  is specified.
 31  
 32  Like other ray tracing shader domains, an intersection shader operates on a
 33  single ray at a time.
 34  It also operates on a single primitive at a time.
 35  It is therefore the purpose of an intersection shader to compute the
 36  ray-primitive intersections and report them.
 37  To report an intersection, the shader calls the code:OpReportIntersectionNV
 38  instruction.
 39  
 40  An intersection shader communicates with any-hit and closest shaders by
 41  generating attribute values that they can: read.
 42  Intersection shaders cannot: read or modify the ray payload.
 43  
 44  [[shaders-intersection-execution]]
 45  === Intersection Shader Execution
 46  The order in which intersections are found along a ray, and therefore the
 47  order in which intersection shaders are executed, is unspecified.
 48  
 49  The intersection shader of the closest AABB which intersects the ray is
 50  guaranteed to be executed at some point during traversal, unless the ray is
 51  forcibly terminated.
 52  
 53  [[shaders-any-hit]]
 54  == Any-Hit Shaders
 55  
 56  The any-hit shader is executed after the intersection shader reports an
 57  intersection that lies within the current [eq]#[tmin,tmax]# of the ray.
 58  The main use of any-hit shaders is to programmatically decide whether or not
 59  an intersection will be accepted.
 60  The intersection will be accepted unless the shader calls the
 61  code:OpIgnoreIntersectionNV instruction.
 62  
 63  [[shaders-any-hit-execution]]
 64  === Any-Hit Shader Execution
 65  
 66  The order in which intersections are found along a ray, and therefore the
 67  order in which any-hit shaders are executed, is unspecified.
 68  
 69  The any-hit shader of the closest hit is guaranteed to be executed at some
 70  point during traversal, unless the ray is forcibly terminated.
 71  
 72  [[shaders-closest-hit]]
 73  == Closest Hit Shaders
 74  
 75  Closest hit shaders have read-only access to the attributes generated by the
 76  corresponding intersection shader, and can: read or modify the ray payload.
 77  They also have access to a number of system-generated values.
 78  Closest hit shaders can: call code:OpTraceNV to recursively trace rays.
 79  
 80  [[shaders-closest-hit-execution]]
 81  === Closest Hit Shader Execution
 82  
 83  Exactly one closest hit shader is executed when traversal is finished and an
 84  intersection has been found and accepted.
 85  
 86  [[shaders-miss]]
 87  == Miss Shaders
 88  
 89  Miss shaders can: access the ray payload and can: trace new rays through the
 90  code:OpTraceNV instruction, but cannot: access attributes since they are not
 91  associated with an intersection.
 92  
 93  [[shaders-miss-execution]]
 94  === Miss Shader Execution
 95  
 96  A miss shader is executed instead of a closest hit shader if no intersection
 97  was found during traversal.
 98  
 99  [[shaders-callable]]
100  == Callable Shaders
101  
102  Callable shaders can: access a callable payload that works similarly to ray
103  payloads to do subroutine work.
104  
105  [[shaders-callable-execution]]
106  === Callable Shader Execution
107  
108  A callable shader is executed by calling code:OpExecuteCallableNV from an
109  allowed shader stage.