dcl_usage (Vertex Shader)

The various types of output registers have been collapsed into 12 o (output) registers (2 for color, 8 for texture, 1 for position, and 1 for fog and point size). These can be used for anything the user wants to interpolate for the pixel shader: texture coordinates, colors, fog, etc.

Output declarations are introduced, whereby semantics are assigned to each register. Old oPos and oPts are replaced by declaring an o register with a position or pointsize semantic, further described here.

There are 12 "out" registers. Ten have 4-components (xyzw) (any 10, not necessarily o0 to o9), another one must be declared as position (all 4-components), and optionally one more can be a scalar point size.

Syntax

The syntax for declaring outputs (o registers) is similar to the declarations for the inputs:

Where:

• _semantics: The same set of semantics as for the input declaration can be used. Semantic names come from the enum D3DDECLUSAGE (and are paired with an index, that is, position3). There always has to be one o register with _positiont0 declaration when not used for process vertices. The positiont0 semantic and the pointsize0 semantic are the only ones that have meaning to Microsoft?Direct3D? beyond simply allowing linkage from vertex to pixel shaders. For shaders with flow control, it is assumed that the worst case output is dcl'd. There are no defaults if a shader does not actually output what it declares it should (due to flow control).
• o: output register. See Output Registers.
• write_mask: The same "out" register can be dcl'd multiple times (so different semantics can be applied to individual components), each time with a unique write mask. However, the same semantic cannot be used multiple times in a declaration -> This means that vectors must be four components or less, and cannot go across four-component register boundaries (individual "out" registers). When the _pointsize semantic is used, it should have full write mask because it is considered a scalar. When the _position semantic is used, it should have a full write mask because all four components have to be written.

Remarks

Vertex shader versions	3_0	3_sw
dcl_usage	x	x

All dcl_usage instructions must appear before the first executable instruction.

Declaration Examples

vs_3_0
dcl_color4     o3.x    // color4 is a semantic name.
dcl_texcoord3  o3.yz   // Different semantics can be packed into one register.
dcl_fog        o3.w 
dcl_tangent	   o4.xyz
dcl_positiont  o7.xyzw // positiont must be declared to some unique register 
                       //   in a vertex shader, with all 4 components.

dcl_psize	   o6      // Pointsize cannot have a mask 
                       //   (that is, mask is full .xyzw) ->
                       // This is an implied scalar register. 
                       // No other semantics can be assigned to any components
                       //   of this register.
                       // If pointsize declaration is not used (typical),
                       //   only 11 "out" registers are available, not 12.
                       // Pixel shaders cannot see this value.