GLSL snippets

Ray marching

// http://jamie-wong.com/2016/07/15/ray-marching-signed-distance-functions/
vec3 rayDirection(float fieldOfView, vec2 size, vec2 fragCoord) {
    vec2 xy = fragCoord - size / 2.0;
    float z = size.y / tan(radians(fieldOfView) / 2.0);
    return normalize(vec3(xy, -z));
}

// http://jamie-wong.com/2016/07/15/ray-marching-signed-distance-functions/
float castRay(const int scene, vec3 eye, vec3 dir,
    float start, float end, float epsilon, int max_marching_steps,
    out int material)
{
    float depth = start;
    for (int i = 0; i < max_marching_steps; i++) {
        float d = sceneSDF(scene, eye + depth * dir, material);
        if (d < epsilon)
            return depth;

        depth += d;
        if (depth >= end)
            break;
    }

    return end;
}

// http://iquilezles.org/www/articles/normalsSDF/normalsSDF.htm
vec3 estimateNormal( const int scene, const float epsilon, in vec3 p )
{
    int m;
    
    const vec2 k = vec2(1,-1);
    return normalize( k.xyy*sceneSDF( scene, p + k.xyy*epsilon, m ) + 
                      k.yyx*sceneSDF( scene, p + k.yyx*epsilon, m ) + 
                      k.yxy*sceneSDF( scene, p + k.yxy*epsilon, m ) + 
                      k.xxx*sceneSDF( scene, p + k.xxx*epsilon, m ) );
}

Matrix transformations

// https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glRotate.xml
mat4 rotate(float a, vec3 v)
{
    float c = cos(a);
    vec3 ci = (1. - c) * v;
    vec3 s = sin(a) * v;

    return mat4(
        ci.x * v.x + c, ci.x * v.y + s.z, ci.x * v.z - s.y, 0,
        ci.y * v.x - s.z, ci.y * v.y + c, ci.y * v.z + s.x, 0,
        ci.z * v.x + s.y, ci.z * v.y - s.x, ci.z * v.z + c, 0,
        0, 0, 0, 1
    );
}

// https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glTranslate.xml
mat4 translate(vec3 v)
{
    return mat4(
        1, 0, 0, 0,
        0, 1, 0, 0,
        0, 0, 1, 0,
        v.x, v.y, v.z, 1
    );
}

Noise

// https://stackoverflow.com/questions/12964279/whats-the-origin-of-this-glsl-rand-one-liner
float rand(vec2 co)
{
    return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453);
}