GLSL Normalize Mouse Input

Question

i'm new in this shader world and just want to try out something. I want to do the following:
In a specific radius around the mouse the texture in the background should rotate by 10°. The mouse coordinates are absolute values, so to work with them i have to normalize them, so i can adress the right space in the texture. But somehow this doesn't work right. The rotation works but i get the color information with a little offset.

I think the problem is the normalize(mouse)but i don't know how to do this right. Here is the shader:

uniform sampler2D tex0;
uniform vec2 mouse;

void main() {
    vec2 pos = vec2(gl_FragCoord.x, gl_FragCoord.y);

    if (distance(pos, mouse) < 90.0) {
        vec2 p = gl_TexCoord[0].st;
        vec2 m = normalize(mouse);

        p.x = m.x + (cos(radians(10.0)) * (p.x - m.x) - sin(radians(10.0)) * (p.y - m.y));
        p.y = m.y + (sin(radians(10.0)) * (p.x - m.x) + cos(radians(10.0)) * (p.y - m.y));

        gl_FragColor = vec4(0.0, m.y, 0.0, 0.0);
        gl_FragColor = texture2D( tex0, p );
    }
    else {
        gl_FragColor.rgb = texture2D( tex0, gl_TexCoord[0].st ).rgb;
        gl_FragColor.a = 1.0;
    }
}

I'm using cinder to do this.

mShader.uniform( "mouse", Vec2f( m.x, 682 - m.y ) );

Thank you.

Answer 1

In order transform absolute mouse coordinates into [0,1] range (required for a texture sample), you don't need normalize function. You need a simple scale:

vec2 mouse_norm = vec2( m.x/screen.width, 1.0 - m.y/screen.height )

I wrote it in GLSL, but for you it will be easier to do on CPU side before passing a uniform, because originally it's CPU side that is aware of the screen resolution.