Problems with Rotation using Float2x2, converting from mat2

Graphics Shaders & Materials
1

Hello,

This is been really bugging me, the resource I’ve been using to learn from, the book of shaders (written in glsl) uses a technique for rotation that I haven’t been able to translate with success.

It’s using a rotation matrix, cos,sin,-sin,cos something like that, the return value is a mat2 in glsl, but the function is set up with a vec2, which doesn’t make sense to me when turning into hlsl, I don’t know how it’s returning a different type.

vec2 rotate(vec2 p, float angle)
{
    float c = cos(angle);
    float s = sin(angle);
   
    return mat2(c,s,-s,c) * p;
}

my ghetto way was just to chop off the end like this below, doesn’t really work if you want to make something specific like a rotating tunnel.

float2 rotate(float2 p, float angle)
{
    float c = cos(angle);
    float s = sin(angle);
   
    return float2(c,s) * p;
}

Does anyone have nay ideas of what to change it to? I know it should be float2x2, but haven’t managed to get it to work, says type mismatch. I’m not quite sure what to do, any thoughts?

2

It’s one of the subtle differences between GLSL and HLSL.

GLSL:
mat2(1,1,1,1) * vec2(1,1);

HLSL:
mul(float2(1,1), float2x2(1,1,1,1));

3 Likes
3

Ahh thank you so much!! That one was killing me!