Registers - vs_2_x

This section contains reference information for the input and output registers implemented by vertex shader version 2_x. Vector elements are designated as x, y, z, w (or the r, g, b, a equivalents).

Input Registers

Name	Register type	Count	Data type	Dimension	I/O permissions	Read port	Read / Instruction	Rel-Address	Defaults	Requires DCL
v#	Input Register	16	floating-point	4-D vector	read	1	3	no	Partial(0001)	yes
r#	Temporary Register	12 (1)	floating-point	4-D vector	read / write	3	3	no	none	no
c#	Constant Float Register	256 (2)	floating-point	4-D vector	define / read	1	2	a0 / aL	(0, 0, 0, 0)	no
i#	Constant Integer Register	16	integer	4-D vector	define / use	1	1	no	(0, 0, 0, 0)	no
b#	Constant Boolean Register	16	boolean	scalar	define / use	1	1	no	FALSE	no
a0	Address Register	1	integer	4-D vector	write / use	1	2	no	none	no
aL	Loop Counter Register	1	integer	scalar	use	1	2	no	none	no
p0	Predicate	1	boolean	4-D vector	write / use	1	1	no	none	no

Where:

partial(x, y, z, w) - If only a subset of channels are updated in the register, the remaining channels will default to specified values (x, y, z, w).
The number of readports is the number of different registers (for each register type) that can be read in a single instruction. For example, a readport of two for a constant register means that all of these are legal since they use 2 or fewer unique constant registers:
```
mad r0, c0, c0, c1 
mad r0, c2, t1, c1 
mad r0, c3, c3, c3 
```
But the following is illegal because it uses mnore than 2 unique constant registers:
```
mad r0, c1, c2, c3
```

(1) - 12 is the minimum r# register counted required by vs_2_x. The D3DCAPS9.VS20Caps.NumTemps cap contains the actual r# register count supported by the device. See D3DCAPS9.

(2) - 256 is the minimum c# register count required by vs_2_x. The MaxVertexShaderConst cap contains the actual c# register count supported by the device. See D3DCAPS9.

Output Registers

Name	Register type	Count	Data type	Dimension	I/O permissions	Rel-Address	Default	Require DCL
oD#	Diffuse/Specular Register	2 (3)	floating-point	4-D vector	write	no	none	no
oFog	Fog Register	1	floating-point	scalar	write	no	none	no
oPos (4)	Position Register	1	floating-point	4-D vector	write	no	none	no
oPts	Point Size Register	1	floating-point	scalar	write	no	none	no
oT#	Texture Coordinates Register	8	floating-point	4-D vector	write	no	none	no

(3) oD0 = diffuse color; oD1 = specular color.

(4) All four components of oPos must be written.