Register Modifiers

Use source register modifiers to change the value read from a register before an instruction runs. The contents of a source register are left unchanged. Modifiers are useful for adjusting the range of register data in preparation for the instruction. A set of modifiers called selectors copies or replicates the data from a single channel (r,g,b,a) into the other channels.

Version 1_4 shaders have modifier functionality specific to shader instructions texld and texcrd. These modifiers affect version 1_4 texture registers and are detailed in Texture Register Modifiers.

Source register modifiers	Syntax	Version
Source register modifiers	Syntax	1_1	1_2	1_3	1_4
bias	register_bias	X	X	X	X
invert	1 - register	X	X	X	X
negate	- register	X	X	X	X
scale by 2	register_x2				X
signed scaling	register_bx2	X	X	X	X

Source register modifiers can be used only on arithmetic instructions. They cannot be used on texture address instructions. The exception to this is the Scale x 2 modifier (_bx2). For version 1_1, signed scale can be used on the source argument of any texm* instruction. For version 1_2 or 1_3, signed scale can be used on the source argument of any texture address instruction.

Some modifier specific restrictions:

Negate can be combined with either the bias, signed scaling, or scalex2 modifier. When combined, negate is run last.
Invert cannot be combined with any other modifier.
Invert, negate, bias, signed scaling, and scalex2 can be combined with any of the selectors.
Source register modifiers should not be used on constant registers because they will cause undefined results. For version 1_4, modifiers on constants are not allowed and will fail validation.