bem

Direct3D 8 - Pixel Shader - Instructions - bem

Last edited 2026-02-20

The bem instruction is used to distort texCoord based on a different texture

The bem syntax looks like this:

bem r.xy, x, y;

r.xy: Register where the information is to be saved (Final result only for the x and y vector)

x: First input register (r#)

y: The second input register (r#) that applies the offset.

Rules for using bem:

bem must appear in the first phase of a shader (that is, before a phase marker).
bem consumes two arithmetic instruction slots.
Only one use of this instruction is allowed per shader.
Destination writemask must be .rg /.xy.
This instruction cannot be co-issued.
Aside from the restriction that destination write mask be .rg, modifiers on source src0, src1, and instruction modifiers are unconstrained.

texture T_Image; // <- Main texture

texture T_Background; // <- Background texture

technique tech_main

{

pass P0

{

Texture[0] = <T_Image>;

Texture[2] = <T_Background>;

PixelShader = asm

{

ps.1.4; // <- Pixel shader version

// --- PHASE 1 --- //

texld r0, t0; // <- Load the T_Image texture

texld r1, t0; // <- Load the T_Background texture

texld r2, t0; // <- Load dump texture

bem r2.xy, r1, r0; // <- Assign a new texCoord offset to Dump texture for red and green color (.xy)

// --- PHASE 2 --- //

phase; // <- Change from phase 1 to phase 2

texld r0, r2; // <- Load the img texture with texCoord distortion (from dump texture / r2)

};

}

Type	Instruction	Description	Instruction slots	ps.1.0	ps.1.1	ps.1.2	ps.1.3	ps.1.4	Note
asm	bem	Apply a fake bump environment-map transform	2	No	No	No	No	Yes	Used to modify texCoords based on two texture.