Texture Register Modifiers

Two pixel shader version 1_4 texture address instructions, texld and texcrd, have custom syntax. These instructions support their own set of source register modifiers, source register selectors, and destination-register write masks, as shown here.

Source Register Modifiers for texld and texcrd

These modifiers provide projective divide functionality by dividing the x and y values by either the z or w values.

Source register modifiers	Description	Syntax	Version
_dz	Divide x,y components by z	source register_dz	1_4
_db	Divide x,y components by z	source register_db	1_4
_dw	Divide x,y components by w	source register_dw	1_4
_da	Divide x,y components by w	source register_da	1_4

Remarks

The _dz or _db modifier does the following:

x^' = x/z ( x^' = 1.0 if z == 0)
y^' = y/z ( y^' = 1.0 if z == 0)
z^' is undefined
w^' is undefined

The _dw or _da modifier does the following:

x^' = x/w ( x^' = 1.0 if w == 0)
y^' = y/w ( y^' = 1.0 if w == 0)
z^' is undefined
w^' is undefined

Source Register Selectors for texld and texcrd

Selectors replicate the contents of one channel into other channels. Replicating the contents of a channel to one or more other channels is commonly referred to as "swizzling."

Source register selectors	Description	Syntax	Version
xyz	Maps x,y,z data to channels x,y,z,z	source register.xyz	1_4
rgb	Maps x,y,z data to channels x,y,z,z	source register.rgb	1_4
xyw	Maps x,y,w data to channels x,y,w,w	source register.xyw	1_4
rga	Maps x,y,w data to channels x,y,w,w	source register.rga	1_4

Remarks

The texld and texcrd instructions never read more than the first three components. So, these selectors provide the option of taking the third component from either the third or the fourth component of the source register.

Destination Register Write Masks for texld and texcrd

Write masks control which channels (red, green, blue, alpha) are updated in the destination register.

Destination register write masks	Description	Syntax	Used by	Version
xyzw	Updates the x,y,z,w channels	destination register.xyzw	texld only	1_4
rgba		destination register.rgba	texld only	1_4
none		destination register	texld only	1_4
xyz	Updates the x,y,z channels	destination register.xyz	texcrd only	1_4
rgb	Updates the x,y,z channels	destination register.rgb	texcrd only	1_4
xy	Updates the x,y channels	destination register.xy	texcrd only	1_4
rg	Updates the x,y channels	destination register.rg	texcrd only	1_4