System-value semantics for the rasterizer stage.

Semantics Supported Only for Direct3D 10 and Newer.

The following types of semantics have been newly introduced for Direct3D 10 and are not available to Direct3D 9.

System-Value
Semantics

System-Value
Semantics

System-value semantics are new to Direct3D 10. All system-values begin with an SV_ prefix, a common example is SV_POSITION, which is interpreted by the rasterizer stage. The system-values are valid at other parts of the pipeline. For instance, SV_Position can
be specified as an input to a vertex shader as well as an output. Pixel shaders can only write to parameters with the SV_Depth and SV_Target system-value semantics.

Other system values (SV_VertexID, SV_InstanceID, SV_IsFrontFace) can only be input into the first active shader in the pipeline that can interpret the particular value; after that the shader function must pass the values to subsequent stages.

SV_PrimitiveID is an exception to this rule of only being input into the first active shader in the pipeline that can interpret the particular value; the hardware can provide the same ID value as input to the hull-shader stage, domain-shader stage, and after
that whichever stage is the first enabled: geometry-shader stage or pixel-shader stage.

If tessellation is enabled, the hull-shader stage and domain-shader stage are present. For a given patch, the same PrimitiveID applies to the patch's hull-shader invocation, and all tessellated domain shader invocations. The same PrimitiveID also propagates
to the next active stage; geometry-shader stage or pixel-shader stage if enabled.

If the geometry shader inputs SV_PrimitiveID and because it can output zero or one or more primitives per invocation, the shader must program its own choice of SV_PrimitiveID value for each output primitive if a subsequent pixel shader inputs SV_PrimtiveID.

As another example, SV_PrimitiveID cannot be interpreted by the vertex-shader stage because a vertex can be a member of multiple primitives.

These semantics have been added to Direct3D 10; they are not available in Direct3D 9.

System-value semantics for the rasterizer stage.

System-Value Semantic	Description	Type
SV_ClipDistance	Clip distance data. SV_ClipDistance values are each assumed to be a float32 signed distance to a plane. Primitive setup only invokes rasterization on pixels for which the interpolated plane distance(s) are >= 0. Multiple clip planes can be implemented simultaneously, by declaring multiple component(s) of one or more vertex elements as the SV_ClipDistance. The combined clip and cull distance values are at most D3D#_CLIP_OR_CULL_DISTANCE_COUNT components in at most D3D#_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT registers. Available to all shaders to be read or written to, except the vertex shader which can write the value but not take it as input. The clipplanes attribute works like SV_ClipDistance but works on all hardware feature level 9_x and higher. For more info, see User clip planes on feature level 9 hardware.	float
SV_CullDistance	Cull distance data. When component(s) of vertex Element(s) are given this label, these values are each assumed to be a float32 signed distance to a plane. Primitives will be completely discarded if the plane distance(s) for all of the vertices in the primitive are < 0. Multiple cull planes can be used simultaneously, by declaring multiple component(s) of one or more vertex elements as the SV_CullDistance. The combined clip and cull distance values are at most D3D#_CLIP_OR_CULL_DISTANCE_COUNT components in at most D3D#_CLIP_OR_CULL_DISTANCE_ELEMENT_COUNT registers. Available to all shaders to be read or written to, except the vertex shader which can write the value but not take it as input.	float
SV_Coverage	A mask that can be specified on input, output, or both of a pixel shader. For SV_Coverage on a pixel shader, OUTPUT is supported on ps_4_1 or higher. For SV_Coverage on a pixel shader, INPUT requires ps_5_0 or higher.	uint
SV_Depth	Depth buffer data. Can be written or read by any shader.	float
SV_DepthGreaterEqual(n)	Valid in any shader, tests whether the value is greater than or equal to the depth data value.	unknown
SV_DepthLessEqual(n)	Valid in any shader, tests whether the value is less than or equal to the depth data value.	unknown
SV_DispatchThreadID	Defines the global thread offset within the Dispatch call, per dimension of the group. Available as input to compute shader. (read only)	uint3
SV_DomainLocation	Defines the location on the hull of the current domain point being evaluated. Available as input to the domain shader. (read only)	float2|3
SV_GroupID	Defines the group offset within a Dispatch call, per dimension of the dispatch call. Available as input to the compute shader. (read only)	uint3
SV_GroupIndex	Provides a flattened index for a given thread within a given group. Available as input to the compute shader. (read only)	uint
SV_GroupThreadID	Defines the thread offset within the group, per dimension of the group. Available as input to the compute shader. (read only)	uint3
SV_GSInstanceID	Defines the instance of the geometry shader. Available as input to the geometry shader. The instance is needed as a geometry shader can be invoked up to 32 times on the same geometry primitive.	uint
SV_InnerCoverage	Represents underestimated conservative rasterization information (i.e. whether a pixel is guaranteed-to-be-fully covered). Can be read or written by the pixel shader.
SV_InsideTessFactor	Defines the tessellation amount within a patch surface. Available in the hull shader for writing, and available in the domain shader for reading.	float|float[2]
SV_InstanceID	Per-instance identifier automatically generated by the runtime (see Using System-Generated Values (Direct3D 10)). Available to all shaders.
SV_IsFrontFace	Specifies whether a triangle is front facing. For lines and points, IsFrontFace has the value true. The exception is lines drawn out of triangles (wireframe mode), which sets IsFrontFace the same way as rasterizing the triangle in solid mode. Can be written to by the geometry shader, and read by the pixel shader.	bool
SV_OutputControlPointID	Defines the index of the control point ID being operated on by an invocation of the main entry point of the hull shader. Can be read by the hull shader only.	uint
SV_Position	When SV_Position is declared for input to a shader, it can have one of two interpolation modes specified: linearNoPerspective or linearNoPerspectiveCentroid, where the latter causes centroid-snapped xyzw values to be provided when multisample antialiasing. When used in a shader, SV_Position describes the pixel location. Available in all shaders to get the pixel center with a 0.5 offset.	float4
SV_PrimitiveID	Per-primitive identifier automatically generated by the runtime (see Using System-Generated Values (Direct3D 10)). Can be written to by the geometry or pixel shaders, and read by the geometry, pixel, hull or domain shaders.	uint
SV_RenderTargetArrayIndex	Render-target array index. Applied to geometry shader output and indicates the render target array slice that the primitive will be drawn to by the pixel shader. SV_RenderTargetArrayIndex is only valid if the render target is an array resource. This semantic applies only to primitives, if a primitive has more than one vertex the value from the leading vertex will be used. This value also indicates which array slice of a depthstencilview is used for read/write purposes. Can be written from the geometry shader and read or written by the pixel shader.	uint
SV_SampleIndex	Sample frequency index data. Available to be read or written to by the pixel shader only.	uint
SV_StencilRef	Represents the current pixel shader stencil reference value. Can be read by the pixel shader only.	int
SV_Target , where 0 <= n <= 7	The output value that will be stored in a render target. The index indicates which of the 8 possibly bound render targets to write to. The value is available to all shaders.	float
SV_TessFactor	Defines the tessellation amount on each edge of a patch. Available for writing in the hull shader and reading in the domain shader.	float[2|3|4]
SV_VertexID	Per-vertex identifier automatically generated by the runtime (see Using System-Generated Values (Direct3D 10)). Available as the input to the vertex shader only.	uint
SV_ViewportArrayIndex	Viewport array index. Applied to geometry shader output and indicates which viewport to use for the primitive currently being written out. Can be read or written by the pixel shader. The primitive will be transformed and clipped against the viewport specified by the index before it is passed to the rasterizer. This semantic applies only to primitives, if a primitive has more than one vertex the value from the leading vertex will be used.	uint

Limitations
when writing SV_Depth:

When multisampling (MultisampleEnable is TRUE in D3D10_RASTERIZER_DESC)
and writing a depth value (using a pixel shader), the single value written out is also used in the depth
test; so the ability to render primitive edges at higher resolution is lost when multisampling.
When using dynamic-flow control, it is impossible to determine at compile time whether a shader that writes SV_Depth in some paths will be guaranteed to write SV_Depth in every execution. Failure to write SV_Depth when declared results in undefined behavior
(which may or may not include discard of the pixel).
Any float32 value including +/-INF and NaN can be written to SV_Depth.
Writing SV_Depth is still valid when performing Dual Source Color Blending.

Migration
from Direct3D 9 to Direct3D 10 and later

The following issues should be considered when migrating code from Direct3D 9 to Direct3D 10 and later:

Mapping
to Direct3D 9 Semantics

A few of the Direct3D 10 and later semantics map directly to Direct3D 9 semantics.

Direct3D 10 Semantic	Direct3D 9 Equivalent Semantic
SV_Depth	DEPTH
SV_Position	POSITION
SV_Target	COLOR

Note to Direct3D 9 developers: For Direct3D 9 targets, shader semantics must map to valid Direct3D 9 semantics. For backwards compatibility POSITION0 (and its variant names) is treated as SV_Position, COLOR is treated as SV_TARGET.

Direct3D
9 VPOS and Direct3D 10 SV_Position

The D3D10 semantic SV_Position provides similar functionality to the Direct3D 9 shader model 3 VPOS semantic. For instance, in Direct3D 9 the following syntax is used for a pixel shader using screen space coordinates:

float4 psMainD3D9( float4 screenSpace : VPOS ) : COLOR
{
  // code here	
}

VPOS was added for shader model 3 support, to specify screen space coordinates, since the POSITION semantic was intended for object-space coordinates.

In Direct3D 10 and later, the SV_Position semantic (when used in the context of a pixel shader) specifies screen space coordinates (offset by 0.5). Therefore, the Direct3D 9 shader would be roughly equivalent (without accounting for the 0.5 offset) to the following:

float4 psMainD3D10( float4 screenSpace : SV_Position ) : COLOR
{
  // code here
}

When migrating from Direct3D 9 to Direct3D 10 and later, you will need to be aware of this when translating your shaders.

User
clip planes in HLSL

Starting with Windows 8, you can use the clipplanes function attribute in an HLSL function
declaration rather than SV_ClipDistance to make your shader work on feature
level 9_x as well as feature level 10 and higher. For more info, seeUser
clip planes on feature level 9 hardware.

Double
Binding Semantics

You can apply the same semantic to more than one parameter. For instance:

float4x4 WorldView[60] : WORLDVIEW : register(c16);
 
float4 main( float3 Pos : SV_POSITION, int4 IPos : SV_POSITION ) : SV_POSITION
{
    float3 P = mul(float4(Pos, 1), (float4x3)WorldView[IPos.w]);
    return float4(P,1);        
}

This function takes two arguments: a three-component, floating-point position and a four-component, integer position. The integer position is used as an index into the array of world-view matrices.

Shader Model 5 implements the system
values from Shader Model 4 and earlier, as well as the following new system values:

SV_DispatchThreadID
SV_DomainLocation
SV_GroupID
SV_GroupIndex
SV_GroupThreadID
SV_GSInstanceID
SV_InsideTessFactor
SV_OutputControlPointID
SV_TessFactor