simple 2d sdf of a heart

heart.glsl

float box(vec2 p){
  vec2 q = abs(p);
  return max(q.x,q.y);
}

// /.-\
// |  |
// \  / <- center is here, it's a bit top-heavy
//  \/ 
float heart(vec2 p){
  vec2 q = abs(p);
  return mix(
    box(vec2(p.x-p.y,p.x+p.y))/sqrt(2.),
    length(q-(q.x*q.x+q.y*q.y)/(2.*(q.x+q.y))),
    step(0.,p.y));
}