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src/graphics/shaders/distance-fs.glsl

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+#version 300 es
+
+precision lowp float;
+
+#define LINE_COUNT {lineCount}
+#define BLOB_COUNT {blobCount}
+
+#define SURFACE_OFFSET 0.001
+ 
+uniform float maxMinDistance;
+uniform float distanceNdcPixelSize;
+
+in vec2 position;
+
+float smoothMin(float a, float b)
+{
+    const float k = 2.0;
+    
+    a = pow(a, k);
+    b = pow(b, k);
+    return pow((a * b) / (a + b), 1.0 / k);
+}
+
+#if LINE_COUNT > 0
+    uniform struct {
+        vec2 from;
+        vec2 toFromDelta;
+        float fromRadius;
+        float toRadius;
+    }[LINE_COUNT] lines;
+
+    void lineMinDistance(inout float minDistance, inout float color) {
+        float myMinDistance = maxMinDistance;
+        for (int i = 0; i < LINE_COUNT; i++) {
+            vec2 targetFromDelta = position - lines[i].from;
+            vec2 toFromDelta = lines[i].toFromDelta;
+            
+            float h = clamp(
+                dot(targetFromDelta, toFromDelta) / dot(toFromDelta, toFromDelta),
+                0.0, 1.0
+            );
+
+            float lineDistance = -mix(
+                lines[i].fromRadius, lines[i].toRadius, h
+            ) + distance(
+                targetFromDelta, toFromDelta * h
+            );
+
+            myMinDistance = min(myMinDistance, lineDistance);
+        }
+
+        color = mix(0.0, color, step(distanceNdcPixelSize + SURFACE_OFFSET, -myMinDistance));
+        minDistance = -myMinDistance;
+    }
+#endif
+
+#if BLOB_COUNT > 0
+    uniform struct {
+        vec2 headCenter;
+        vec2 leftFootCenter;
+        vec2 rightFootCenter;
+        float headRadius;
+        float footRadius;
+        float k;
+    }[BLOB_COUNT] blobs;
+
+    float circleMinDistance(vec2 circleCenter, float radius) {
+        return distance(position, circleCenter) - radius;
+    }
+
+    void blobMinDistance(inout float minDistance, inout float color) {
+        for (int i = 0; i < BLOB_COUNT; i++) {
+            float headDistance = circleMinDistance(blobs[i].headCenter, blobs[i].headRadius);
+            float leftFootDistance = circleMinDistance(blobs[i].leftFootCenter, blobs[i].footRadius);
+            float rightFootDistance = circleMinDistance(blobs[i].rightFootCenter, blobs[i].footRadius);
+
+            float res = min(
+                smoothMin(headDistance, leftFootDistance),
+                smoothMin(headDistance, rightFootDistance)
+            );
+
+            res = min(100.0, headDistance);
+            res = min(res, leftFootDistance);
+            res = min(res, rightFootDistance);
+            //color = mix(2.0, color, step(distanceUvPixelSize + SURFACE_OFFSET, res));
+            minDistance = min(minDistance, res);
+            color = mix(2.0, color, step(distanceNdcPixelSize + SURFACE_OFFSET, res));
+        }
+    }
+#endif
+
+out vec2 fragmentColor;
+
+void main() {
+    float minDistance = -maxMinDistance;
+    float color = 0.0;
+
+    #if LINE_COUNT > 0
+        lineMinDistance(minDistance, color);
+    #endif
+
+    #if BLOB_COUNT > 0
+        blobMinDistance(minDistance, color);
+    #endif
+
+
+    // minDistance / 2.0: NDC to UV scale
+    fragmentColor = vec2((minDistance - SURFACE_OFFSET) / 2.0, color);
+}