From 3502dcfcb0b7dc6a49369a437bf96f137393c15a Mon Sep 17 00:00:00 2001
From: schmelczerandras <andras@schmelzer.dev>
Date: Sat, 11 Jul 2020 22:16:25 +0200
Subject: [PATCH] Add skeleton for distance shader

---
 frontend/src/shaders/dist.frag | 97 ++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 frontend/src/shaders/dist.frag

diff --git a/frontend/src/shaders/dist.frag b/frontend/src/shaders/dist.frag
new file mode 100644
index 0000000..0affcde
--- /dev/null
+++ b/frontend/src/shaders/dist.frag
@@ -0,0 +1,97 @@
+#ifdef GL_ES
+precision mediump float;
+#endif
+
+#define INFINITY 1.0 / 0.0
+
+#define WORLD_SIZE 4
+
+#define N (20)
+
+uniform vec2 u_resolution;
+uniform vec2 u_mouse;
+uniform float u_time;
+
+struct Light {
+    vec2 center;
+  	float radius;
+    vec3 color;
+    float intensity;
+};
+
+struct Circle {
+    vec2 center;
+  	float radius;
+    vec3 color;
+};
+
+Circle world[WORLD_SIZE];
+
+vec3 red = vec3(5.0, 0.0, 2.0);
+vec3 blue = vec3(0.0, 0.0, 3.0);
+
+float sdPolygon( in vec2[N] v, in vec2 p )
+{
+    float d = dot(p-v[0],p-v[0]);
+    float s = 1.0;
+    const int num = v.length();
+    for( int i=0, j=num-1; i<N; j=i, i++ )
+    {
+        vec2 e = v[j] - v[i];
+        vec2 w = p - v[i];
+        vec2 b = w - e*clamp( dot(w,e)/dot(e,e), 0.0, 1.0 );
+        d = min( d, dot(b,b) );
+        bvec3 c = bvec3(p.y>=v[i].y,p.y<v[j].y,e.x*w.y>e.y*w.x);
+        if( all(c) || all(not(c)) ) s*=-1.0;  
+    }
+    return s*sqrt(d);
+}
+
+float circleDistance(in vec2 position, in Circle circle)
+{
+	return length(position - circle.center) - circle.radius;
+}
+
+float circleDistance(in vec2 position, in Light circle)
+{
+	return length(position - circle.center) - circle.radius;
+}
+
+float getDistance(in vec2 target) {
+    float distance = INFINITY;
+    for (int i = 0; i < WORLD_SIZE; i++) {
+        distance = min(distance, circleDistance(target, world[i]));
+    }
+    return distance;
+}
+
+float getDistance(in vec2 target, out Circle nearest) {
+    float distance = INFINITY;
+    for (int i = 0; i < WORLD_SIZE; i++) {
+        float distanceToCurrent = circleDistance(target, world[i]);
+        if (distanceToCurrent < distance) {
+            distance = distanceToCurrent;
+            nearest = world[i];
+        }
+    }
+    return distance;
+}
+
+void createWorld() {
+    world[0] = Circle(vec2(250.0, 100.0), 12.5, blue);   
+    world[1] = Circle(vec2(150.0, 50.0), 32.5, red);
+    world[2] = Circle(vec2(300.0, 350.0), 52.5, blue);
+}
+
+float linearstep(float a, float b, float q) {
+    return a + clamp((b - a) * q, 0.0, 1.0);
+}
+
+void main() {
+    createWorld();
+    
+    vec2 position = gl_FragCoord.xy + vec2(0.5);
+    
+    vec3 color = vec3(1.0) * linearstep(0.0, 1.0, getDistance(position));
+    gl_FragColor = vec4(color, 1.0);
+}