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UUSL Semantics

Redefined UUSL semantics allows you to create unified input\output shader structures for both graphics APIs.

Vertex Shader Semantics#

Vertex shader semantics contain necessary input and output data for shader. You should initialize variables first and then use them.

UUSL Direct3D Description
INIT_ATTRIBUTE(TYPE,NUM,SEMANTICS) TYPE attribute_ ## NUM : SEMANTICS; Adds a semantic to a vertex shader variable.
INIT_OUT(TYPE,NUM) TYPE data_ ## NUM : TEXCOORD ## NUM; Adds an output data semantic.
INIT_POSITION float4 position : SV_POSITION; Adds a position system-value semantic.
INIT_INSTANCE uint instance : SV_INSTANCEID; Adds a per-instance identifier system-value semantic.
INIT_VERTEX_ID uint vertex_id: SV_VertexID Adds a per-vertex identifier.

Here is an example of vertex shader input and output structures:

UUSL
// Input vertex data
STRUCT(VERTEX_IN)
	INIT_ATTRIBUTE(float4,0,POSITION)	// Vertex position
	INIT_ATTRIBUTE(float4,1,TEXCOORD0)	// Vertex texcoord (uv)
	INIT_ATTRIBUTE(float4,2,TEXCOORD1)	// Vertex basis tangent
	INIT_ATTRIBUTE(float4,3,TEXCOORD2)	// Vertex color
END

// Our output vertex data
STRUCT(VERTEX_OUT)
	INIT_POSITION		// Out projected position
	INIT_OUT(float4,0)	// Texcoord (uv)
	INIT_OUT(float3,1)	// Vertex direction
END

Use the following pre-defined variables to use the input\output vertex shader semantics:

UUSL Direct3D Description
IN_INSTANCE input.instance An input per-instance identifier system-value variable.
IN_ATTRIBUTE(NUM) input.attribute_ ## NUM An input shader variable.
IN_VERTEX_ID input.vertex_id An input per-vertex identifier.
OUT_DATA(NUM) output.data_ ## NUM An output texture coordinates variable.
OUT_POSITION output.position An output position system-value variable.

Fragment Shader Semantics#

Fragment shader semantics contain necessary input and output data for shader. You should initialize variables first and then use them.

UUSL Direct3D Description
INIT_IN(TYPE,NUM) TYPE data_ ## NUM : TEXCOORD ## NUM; Adds an input texture coordinates semantic.
INIT_COLOR(TYPE) TYPE color : SV_TARGET; Add an output diffuse or specular color semantic (single RT).
INIT_DEPTH float depth : SV_DEPTH; Add an output depth system-value semantic.
INIT_MRT(TYPE,NUM) TYPE color_ ## NUM : SV_TARGET ## NUM; Add an output color system-value semantic (some RTs).
INIT_FRONTFACE bool frontface : SV_ISFRONTFACE; Adds an input semantic indicates primitive face (frontface or not).

To use the variables in the code, use the following variables:

UUSL Direct3D Description
IN_POSITION input.position An input position value.
IN_DATA(NUM) input.data_ ## NUM An input texture coordinates variable.
IN_FRONTFACE input.frontface Floating-point scalar that indicates a back-facing primitive. A negative value faces backwards, while a positive value faces the camera.
OUT_COLOR output.color An output color value (single RT).
OUT_DEPTH output.depth An output depth value.
OUT_MRT(NUM) output.color_ ## NUM An output color value for MRTs.

Here is a simple example of using the variable in the main function of the shader:

USUL
MAIN_FRAG_BEGIN(FRAGMENT_IN)
	
	float4 texcoord = IN_DATA(0);

	/* ... other code ... */
MAIN_FRAG_END

Geometry Shader Semantics#

UUSL Direct3D Description
INIT_GEOM_IN(TYPE,NUM) TYPE data_ ## NUM : TEXCOORD ## NUM; Add an input texture coordinates semantic for the geometry-shader stage.
INIT_GEOM_OUT(TYPE,NUM) TYPE data_ ## NUM : TEXCOORD ## NUM; Add an output texture coordinates semantic for the geometry-shader stage.
UUSL Direct3D Description
IN_GEOM_DATA(NUM,INDEX) input[INDEX].data_ ## NUM An input texture coordinates value.
IN_GEOM_POSITION(INDEX) input[INDEX].position An input position value.
OUT_GEOM_DATA(NUM) output.data_ ## NUM An output texture coordinates value.
TRIANGLE_IN triangle Input primitive type: triangle list or triangle strip.
TRIANGLE_OUT TriangleStream Output primitive type: a sequence of triangle primitives
LINE_IN line Input primitive type: line.
LINE_OUT LineStream Output primitive type: a sequence of line primitives

Unified Shader Semantics#

Unified shader semantics allows you to create single structure for both vertex and fragment shaders. It facilitates the work with vertex and fragment shaders input/output structure by using single structure for both shaders: this structure will be output for vertex shader and input for fragment shader respectively.

You can write vertex and fragment shader in a single file with .shader extension. In this case, in the material you should specify this .shader file for both shader stages.

Source code (XML)
BaseMaterial <texture_prefix=tex var_prefix=var>
{
	// ...

	Pass auxiliary if [auxiliary]
	{
		Vertex = "core/materials/base/objects/mesh/shaders/auxiliary/auxiliary.shader"
		Fragment = "core/materials/base/objects/mesh/shaders/auxiliary/auxiliary.shader"
	}

	// ..
}
UUSL VERTEX FRAGMENT Description
INIT_DATA(TYPE,NUM,NAME) INIT_OUT(TYPE,NUM) \ #define NAME GET_DATA(NUM) INIT_IN(TYPE,NUM) \ #define NAME GET_DATA(NUM) Data initialization.
GET_DATA(V) OUT_DATA(V) IN_DATA(V) Helper for getting/setting data by using data name.

IF statement#

There is also the IF_DATA(NAME) statement to execute an operation if the data is not null.

UUSL VERTEX FRAGMENT Description
IF_DATA(NAME) #ifdef NAME #ifdef NAME Opening IF conditional statement.
ENDIF #endif #endif Closing IF conditional statement.

Here is a code snippet of shader, where the shader's IF statement is used.

UUSL
//input struct
STRUCT(FRAGMENT_IN)
/* ... */
	#ifdef ALPHA_FADE && USE_ALPHA_FADE
		INIT_DATA(float,1,DATA_ALPHA_FADE)
	#endif
/* ... */
END

//main functions
MAIN_FRAG_BEGIN(FRAGMENT_IN)
/* ... */
	IF_DATA(DATA_ALPHA_FADE)
		//code to execute if the data is not null
		alphaFadeDiscard(DATA_ALPHA_FADE,IN_POSITION.xy);
	ENDIF
/* ... */
MAIN_FRAG_END

Interpolation Modifiers#

UUSL Direct3D Description
MODIFER_LINEAR linear Interpolate between shader inputs; linear is the default value if no interpolation modifier is specified.
MODIFER_CENTROID centroid Interpolate between samples that are somewhere within the covered area of the pixel (this may require extrapolating end points from a pixel center). Centroid sampling may improve antialiasing if a pixel is partially covered (even if the pixel center is not covered). The centroid modifier must be combined with either the linear or noperspective modifier.
MODIFER_NOINTERPOLATION nointerpolation Do not interpolate.
MODIFER_NOPERSPECTIVE noperspective Do not perform perspective-correction during interpolation. The noperspective modifier can be combined with the centroid modifier.
MODIFER_SAMPLE sample Interpolate at sample location rather than at the pixel center. This causes the pixel shader to execute per-sample rather than per-pixel.

See Also#

See also the article on Interpolation Modifiers.

Last update: 2024-08-16
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