shader-sdf

Shader SDFs

Signed Distance Functions return the distance from a point to a shape's surface. Negative = inside, positive = outside, zero = on surface.

Quick Start

// 2D circle SDF
float sdCircle(vec2 p, float r) {
  return length(p) - r;
}

// Usage
float d = sdCircle(uv - 0.5, 0.3);

// Render
vec3 color = d < 0.0 ? vec3(1.0) : vec3(0.0);           // Hard edge
vec3 color = vec3(smoothstep(0.01, 0.0, d));            // Soft edge
vec3 color = vec3(smoothstep(0.02, 0.0, abs(d)));       // Outline

2D Primitives

Circle

float sdCircle(vec2 p, float r) {
  return length(p) - r;
}

Box

float sdBox(vec2 p, vec2 b) {
  vec2 d = abs(p) - b;
  return length(max(d, 0.0)) + min(max(d.x, d.y), 0.0);
}

Rounded Box

float sdRoundedBox(vec2 p, vec2 b, float r) {
  vec2 d = abs(p) - b + r;
  return length(max(d, 0.0)) + min(max(d.x, d.y), 0.0) - r;
}

Line Segment

float sdSegment(vec2 p, vec2 a, vec2 b) {
  vec2 pa = p - a;
  vec2 ba = b - a;
  float h = clamp(dot(pa, ba) / dot(ba, ba), 0.0, 1.0);
  return length(pa - ba * h);
}

Triangle

float sdTriangle(vec2 p, vec2 p0, vec2 p1, vec2 p2) {
  vec2 e0 = p1 - p0, e1 = p2 - p1, e2 = p0 - p2;
  vec2 v0 = p - p0, v1 = p - p1, v2 = p - p2;
  vec2 pq0 = v0 - e0 * clamp(dot(v0, e0) / dot(e0, e0), 0.0, 1.0);
  vec2 pq1 = v1 - e1 * clamp(dot(v1, e1) / dot(e1, e1), 0.0, 1.0);
  vec2 pq2 = v2 - e2 * clamp(dot(v2, e2) / dot(e2, e2), 0.0, 1.0);
  float s = sign(e0.x * e2.y - e0.y * e2.x);
  vec2 d = min(min(
    vec2(dot(pq0, pq0), s * (v0.x * e0.y - v0.y * e0.x)),
    vec2(dot(pq1, pq1), s * (v1.x * e1.y - v1.y * e1.x))),
    vec2(dot(pq2, pq2), s * (v2.x * e2.y - v2.y * e2.x)));
  return -sqrt(d.x) * sign(d.y);
}

Ring

float sdRing(vec2 p, float r, float thickness) {
  return abs(length(p) - r) - thickness;
}

Polygon (N-sided)

float sdPolygon(vec2 p, float r, int n) {
  float a = atan(p.x, p.y) + 3.141592;
  float s = 6.283185 / float(n);
  return cos(floor(0.5 + a / s) * s - a) * length(p) - r;
}