Pixel-Composer/shaders/sh_path_sdf/sh_path_sdf.fsh

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform vec2  dimension;
uniform int   subdivision;
uniform float maxDistance;
uniform int   inverted;

uniform vec2 points[1024];

vec2 pointToLine(in vec2 p, in vec2 l0, in vec2 l1) {
	float l2 = pow(l0.x - l1.x, 2.) + pow(l0.y - l1.y, 2.);
	if (l2 == 0.) return l0;
	  
	float t = ((p.x - l0.x) * (l1.x - l0.x) + (p.y - l0.y) * (l1.y - l0.y)) / l2;
	t = clamp(t, 0., 1.);
	
	return mix(l0, l1, t);
}

void main() {
	vec2 px = v_vTexcoord * dimension;
	
	float minDist = 9999.;
	vec2 ox = points[0], nx;
	vec2 p;
	
	for(int i = 1; i < subdivision; i++) {
		nx = points[i];
		p  = pointToLine(px, ox, nx);
		
		float dist = distance(px, p);
		minDist = min(minDist, dist);
		
		ox = nx;
	}
	
	float distC = minDist / maxDistance;
	if(inverted == 1) distC = 1. - distC;
	
	gl_FragColor = vec4(vec3(distC), 1.);
}