# HLSL: UV swap

# Message from 2021

This post is pretty old! Opinions and technical information in it are almost certainly oudated. Commands and configurations will probably not work. Consider the age of the content before putting any of it into practice.

This shader swaps the U and V channels in the YUV color space with a single matrix multiplication. The constants in the matrix are calculated based on wikipedia’s RGB -> YUV matrix, the corresponding YUV -> RGB matrix, and the simple reversing matrix R obtained by:

- Take the 4x4 identity matrix I
- Swap the second and third rows (corresponding to U and V).

Multiply the three matrices RGB->YUV, R, and YUV->RGB. Get a computer to do it because the math is boring.

sampler s0 : register(s0); float4 main(float2 tex : TEXCOORD0) : COLOR { float4x4 matUVshiftRGB = { -0.00029999999999998084, 0.00013179999999999513, 1.0041311, 0, -0.0010000000000000286, 1.004206, 0.00014329999999999492, 0, 1, -.00002499999999975368, 0.00002220000000001008, 0, 0, 0, 0, 0}; // matrix math! return mul(tex2D( s0, tex), matUVshiftRGB); }

This shader was made to use with Media Player Classic.