Can't convert mat2 to float2x2.

Unity Engine
,
1

Hi there, Sorry I’m new to shaders.
I’m having trouble to converting a mat2 Type function(GLSL). I have normally seen vec2 functions, but I can’t seem to find out how to call the equivalent float2x2(HLSL).

GLSL

float s = sin(a);
float c = cos(a);
return mat2(c, -s, s, c);
}```

HLSL
``` float2x2 Rot(float a) {
float s = sin(a);
float c = cos(a);
return float2x2(c, -s, s, c);
}```

OR
```float2 Rot(float a) {
float s = sin(a);
float c = cos(a);
return float2x2(c, -s, s, c);
}```

Function call:
``` float map(float3 p){
p.xy*=Rot(_Time*0.06);
}```

Getting error:: "type mismatch at line xx" ie "p.xy*=Rot(_Time*0.06);"
How do I rewrite the original mat2 function? This seem to run fine on GLSL. I think "rotate" is expecting float2 but that doesn't work.
2

How is rotate defined? Why aren’t you using Rot?

I’m not sure what you want to do exactly, but here is how to rotate some vertices in a shader.

            half4 Rotate (half4 vertex, half degrees) {
                half alpha = degrees * UNITY_PI / 180;
                half sina, cosa;
                sincos(alpha, sina, cosa);
                half2x2 m = half2x2(cosa, -sina, sina, cosa);
                return half4(mul(m, vertex.xy), vertex.zw).xyzw;
            }
3

When you multiply a vector and a matrix together in GLSL you can do myVector *= myMatrix to get the equivalent of myMatrix * myVector.

But in HLSL you don’t use the * operator for matrices this way. You instead need to use the mul() function to multiply matrices by vectors or vice versa. That also means there’s no *= operator where the right hand variable is a matrix, unless the left hand is also a matrix.

So you’ll want:

p.xy = mul(rotate(_Time.y * 0.06), p.xy);

Also note Unity’s _Time is a float4 where _Time.y is the unmodified game time.

2 Likes
4

Thanks, I meant to put in “p.xy*=Rot(_Time0.06);" I don’t think there’s anything wrong with “Rot”. I think I calling it incorrectly ""p.xy=Rot(_Time*0.06)”

5

WOW. Thanks. This worked. → p.xy = mul(rotate(_Time.y * 0.06), p.xy);