cmp

Direct3D 8 - Pixel Shader - Instructions - cmp

Last edited 2026-02-20

The cmp instruction compares whether the parameter y is greater or eqaul than 0, if so it returns z, if not it returns w.

The cmp syntax looks like this:

cmp x, y.*, z, w;

x: The value to which the final value should be assigned.

y: The test parameter to which it should be compared, whether it is greater or eqaul than 0 (see information below for details).

z: The value to be assigned to the final result if true.

w: The value to be assigned to the final result if false.

For Pixel Shader versions: ps.1.2, ps.1.3:

The y parameter can only refer to the alpha color, i.e. you can only use "y.a", for example: r0.a;
Each shader can use up to a maximum of three cmp instructions.;
The destination register cannot be the same as any of the source registers;

For Pixel Shader version ps.1.4, it can be any vector (r, g, b, or a)

texture T_Image; // <- Main texture

technique tech_main

{

pass P0

{

Texture[0] = <T_Image>;

PixelShader = asm

{

ps.1.2; // <- Pixel shader version

def c0, 1.0, 0.0, 0.0, 1.0; // <- Declaration of a constant 0, it's red color

def c1, 0.0, 0.0, 1.0, 1.0; // <- Declaration of a constant 0, it's blue color

tex t0; // <- Load the T_Image texture

mov r0, t0; // <- Assign texture colors to register r0

sub t0.a, t0.a, c1.a; // Subtract 1 from the texture's alpha color

cmp r0, t0.a, c0, c1; // <- Conditional checking

// if (r0.a >= 0.0)

// Assign the color red;

// else

// Assign the color blue;

};

}

Type	Instruction	Description	Instruction slots	ps.1.0	ps.1.1	ps.1.2	ps.1.3	ps.1.4	Note
asm	cmp	Compare source to 0	1	Yes	Yes	Yes	Yes	Yes	An IF/ELSE condition that checks whether the given number is greater or eqaul than 0 and assigns the appropriate color.