Direct3D 8 - Pixel Shader - Instructions - def

Last edited 2026-02-20

The def instruction declares a new vector to a constant value.

It should be used at the beginning of assembly language after the ps instruction.

The def syntax looks like this:

def c#, x, y, z, w;

c#: specifies what constant you want to assign a value to, the "#" should be a number (from 0 to 7), for more details go to the Input/Output Registers page.

x: specifies what value you want to assign to x (from -1.0 to 1.0); the value x can be treated as the color red (alias).

y: specifies what value you want to assign to y (from -1.0 to 1.0); the value y can be treated as the color green (alias).

z: specifies what value you want to assign to z (from -1.0 to 1.0); the value z can be treated as the color blue (alias).

w: specifies what value you want to assign to w (from -1.0 to 1.0); the value w can be treated as the color alpha (alias).

Example code:

texture T_Image;                            // <- Main texture

technique tech_main

{

    pass P0

    {

        Texture[0] = <T_Image>;

        PixelShader = asm

        {

            ps.1.1;                         // <- Pixel shader version

            def c0, 0.2f, 0.5f, -0.1f, 0.5f // <- Declaration of a constant, we treat it as a color (r, g, b, a)

            tex t0;                         // <- Load the T_Image texture

            add r0, c0, t0;                 // <- Assign the addition of colors from the texture and from the constant to the final result: result.rgba = const.rgba + texture.rgba

            mov r0.a, t0.a;

        };

    }

}

This example requires the following in the .XML file:

• Flag <dx8>yes</dx8>

(More information about .XML files can be found here)

Details table:

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