A little heart shader

heart.rs

// cosine based palette, 4 vec3 params
vec3 palette( in float t )
{
    vec3 a = vec3(0.5, 0.1, 0.1);
    vec3 b = vec3(0.7, 0.4, 0.4);
    vec3 c = vec3(1.0, 0.8, 0.8);
    vec3 d = vec3(0.263, 0.416, 0.557);
    return a + b*cos( 6.28318*(c*t+d) );
}

float dot2( in vec2 v ) { return dot(v,v); }

float sdHeart( in vec2 p )
{
    p.x = abs(p.x);

    if( p.y+p.x>1.0 )
        return sqrt(dot2(p-vec2(0.25,0.75))) - sqrt(2.0)/4.0;
    return sqrt(min(dot2(p-vec2(0.00,1.00)),
                    dot2(p-0.5*max(p.x+p.y,0.0)))) * sign(p.x-p.y);
}

// The distance estimator for a sphere
float sphereDE(vec3 pos, vec3 spherePos, float size) {
	return length(pos - spherePos) - size;
}

vec3 march(vec3 origin, vec3 direction) {
    float rayDist = 0.0;
    const int NUM_STEPS = 32; // doesn't matter much right now
    const float MIN_DIST = 0.001; // threshold for intersection
    const float MAX_DIST = 1000.0; // oops we went into space
    
    for(int i = 0; i < NUM_STEPS; i++) {
        vec3 current_pos = origin + rayDist*direction;
        
        // Use our distance estimator to find the distance
        float _distance = sphereDE(current_pos, vec3(0.0), 1.0);
        
        if(_distance < MIN_DIST) {
            // We hit an object! This just adds a subtle shading effect.
            return vec3(rayDist/float(NUM_STEPS)*4.0);
        }
        
        if(rayDist > MAX_DIST) {
            // We have gone too far
            break;
        }
        
        // Add the marched distance to total
        rayDist += _distance;
    }
    // The ray didn't hit anything so return a color (black, for now)
    return vec3(0.0);
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = (fragCoord * 2.0 - iResolution.xy ) / iResolution.y;
    uv.x += cos(0.5 * iTime * 4.);
    uv.y += sin(0.2 * iTime * 4.);

    float d = sdHeart(uv * 4.0);

    vec3 camPos = vec3(0.0, 0.0, -3.0);
    vec3 rayDir = vec3(uv, 1.0);

    vec3 col = palette(d + iTime) * march(camPos, rayDir);
    
    d = sin(d * 8. + iTime)/8.;
    d = abs(d);
    d = 0.004 / d;
    d = smoothstep(0.0, 0.1, d);

    col *= d;
    
    fragColor = vec4(col, 1.0);
}