# m3x3 - ps

Multiplies a 3-component vector by a 3x3 matrix.

## Syntax

m3x3 dst, src0, src1 |
---|

where

- dst is the destination register. Result is a 3-component vector.
- src0 is a source register representing a 3-component vector.
- src1 is a source register representing a 3x3 matrix, which corresponds to the first of 3 consecutive registers.

## Remarks

Pixel shader versions | 1_1 | 1_2 | 1_3 | 1_4 | 2_0 | 2_x | 2_sw | 3_0 | 3_sw |
---|---|---|---|---|---|---|---|---|---|

m3x3 | x | x | x | x | x |

The xyz mask is required for the destination register. Negate and swizzle modifiers are allowed for src0 but not for src1.

The following code snippet shows the operations performed.

```
dest.x = (src0.x * src1.x) + (src0.y * src1.y) + (src0.z * src1.z);
dest.y = (src0.x * src2.x) + (src0.y * src2.y) + (src0.z * src2.z);
dest.z = (src0.x * src3.x) + (src0.y * src3.y) + (src0.z * src3.z);
```

The input vector is in register src0. The input 3x3 matrix is in register src1, and the next two higher registers, as shown in the expansion below. A 3D result is produced, leaving the other element of the destination register (dest.w) unaffected.

This operation is commonly used for transforming normal vectors during lighting computations. This instruction is implemented as a set of dot products as shown below.

```
m3x3 r0.xyz, r1, c0 which will be expanded to:
dp3 r0.x, r1, c0
dp3 r0.y, r1, c1
dp3 r0.z, r1, c2
```

## Related topics