playing with sdf

circle.glsl

float circle(vec2 point, vec2 center, float r)
{
    return distance(point, center) - r;
}

float hollowCircle(vec2 point, vec2 center, float r1, float r2)
{
    float med = (r1+r2)/2.;
    return abs(distance(point, center) - med) - r2 + med;
}

float rect(vec2 point, vec2 center, vec2 size)
{
    point = point - center;
    point.x = abs(point.x);
    point.y = abs(point.y);
    if (point.x > size.x && point.y > size.y) {
        return distance(size, point);
    }
    if (point.x > size.x) {
        return point.x - size.x;
    }
    if (point.y > size.y) {
        return point.y - size.y;
    }
    return max(point.x - size.x, point.y - size.y);
}

float sqr(float x) { return x*x; }
float det(vec2 a, vec2 b) { return a.x*b.y-b.x*a.y; }

float halfPlane(vec2 point, vec2 p0, vec2 p1)
{
    if (distance(p0, p1) < 0.001) {
        // not a line
        return distance(p0, point);
    }
    return det(point - p0, point - p1) / distance(p0, p1);
}

float thing(vec2 point, vec2 p0, vec2 p1, float k)
{
    float d = 0.01 - (exp(-distance(point, p0)/10.) + exp(-distance(point, p1)/10.));
    if (d > 0.005) {
        return min(distance(point, p0), distance(point, p1));
    }
    return d;
    return (-sqr(distance(point, p0)/k));
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 center = iResolution.xy / 2.;
    vec2 h = vec2(iResolution.x / 20., 0);
    float dist;
//    dist = hollowCircle(fragCoord.xy, center, 100., 200.);
//    dist = rect(fragCoord.xy, center, vec2(200., 100.));
//    dist = (circle(fragCoord.xy, center - h, 250.)
//          + circle(fragCoord.xy, center + h, 250.)) / 2.;
//    dist = halfPlane(fragCoord.xy, center, iMouse.xy);
    vec2 xy = mix(fragCoord.xy, center, 0.);
    dist = thing(xy, center - h, center + h, 10.);
    if (dist > 0.) {
        fragColor = vec4(mod(dist/50.,1.),0.,0.,1.);
    } else {
        dist = -dist;
        fragColor = vec4(1.-mod(dist/50.,1.),1.-mod(dist/50.,1.),0.,1.);
    }
//	vec2 uv = fragCoord.xy / iResolution.xy;
//	fragColor = vec4(uv,0.5+0.5*sin(iGlobalTime),1.0);
}

line.glsl

float det(vec2 a, vec2 b) { return a.x*b.y-b.x*a.y; }

float approx_distance(vec2 point, vec2 mouse, vec2 p0, vec2 p1) {
    vec2 dir = mouse - p0;
    if (length(dir) < 0.001) {
        // YOU LIED TO ME, THIS IS NOT A LINE
        return distance(point, p0);
    }
    return abs(det(point - p0, dir) / length(dir));
}

vec4 getColor( in vec2 fragCoord)
{
	vec2 xy = fragCoord.xy;
	
	vec2 p0 = vec2(0.25, .5) * iResolution.xy;
	vec2 p1 = vec2(.75, .5) * iResolution.xy;
	vec2 mouse = iMouse.xy;
	float d = approx_distance(xy, mouse, p0, p1);
	float thickness = 1.0;

    if(d < thickness) {
        return vec4(d/50.,1.,1.,1.);
	} else {
	  // Anti-alias the edge.
      float a = 1.0 - smoothstep(d, thickness, thickness+1.0);
      return vec4(mod(d/50.,1.0),a,a,1.);
	}
}

// anti-aliasing
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec4 sum;
    sum = getColor( fragCoord + vec2(-0.25,-0.25));
    sum = sum + getColor( fragCoord + vec2(-0.25,0.25));
    sum = sum + getColor( fragCoord + vec2(0.25,-0.25));
    sum = sum + getColor( fragCoord + vec2(0.25,0.25));
	fragColor = sum / 4.0;
}