arcFragmentShader.glsl

precision mediump float;

varying vec4 color;
varying vec2 uv;
varying float pixelSize;
varying float innerRadius;
varying vec2 angleUnit;



float sq(float a){ return a*a; }
float clampUnit(float a){ return clamp(a,0.0,1.0); }
float lengthSquared(vec2 a){ return dot(a,a); }
vec2 orthoCloc(vec2 b){ return vec2(b.y, -b.x); }
vec2 orthoCoun(vec2 b){ return vec2(-b.y, b.x); }

float circleOpacity(vec2 uv, float pixelSize, float innerRadius, vec2 angleUnit){
 float dist = length(uv);
 float fringeSpan = 2.0*pixelSize;
 float angleFade;
 float distFromAngleUnit = (dot(uv,orthoCloc(angleUnit))+fringeSpan)/fringeSpan;
 float distFromXAxis = (uv.y + fringeSpan)/fringeSpan;
 if(angleUnit.y > 0.0){
  angleFade = min(distFromAngleUnit, distFromXAxis);
 }else{
  angleFade = max(distFromAngleUnit, distFromXAxis);
 }
 return clampUnit(min(
  min(
   1.0 - dist, //outer fringe
   dist + fringeSpan - innerRadius )/fringeSpan, //inner fringe
  angleFade //angle of the unit thing
 ));
}

void main(){
 float copa = circleOpacity(uv, pixelSize, innerRadius, angleUnit);
 gl_FragColor = vec4(color.rgb, color.a*copa);
  // gl_FragColor = vec4(color.rgb, color.a*circleOpacity(uv, pixelSize, innerRadius, angleUnit));
}