Texture Register Modifiers

Microsoft Directx 8.1 (pixel shader version 1.4)

Texture Register Modifiers for texld and texcrd

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 below.

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		source register_db	1.4
_dw	Divide x,y components by w	source register_dw	1.4
_da		source register_da	1.4

Register

Source register. For more about register types, see Registers.

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

Note  For pixel shader version 1.4, the D3DTTFF_PROJECTED flag under D3DTSS_TEXTURETRANSFORMFLAGS is ignored because a projective divide is accomplished by the source register modifiers listed previously.

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		source register.rgb	1.4
xyw	Maps x,y,w data to channels x,y,w,w	source register.xyw	1.4
rga		source register.rga	1.4

Register

Source register. For more about register types, see Registers.

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		destination register.rgb	texcrd only	1.4
xy	Updates the x,y channels	destination register.xy	texcrd only	1.4
rg		destination register.rg	texcrd only	1.4

Register

Destination register. For more about register types, see Registers.