Create SmoothEllipseShader.c

Retina Display support for ellipse()

Author: FeynmanTech

SmoothEllipseShader.c

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+//
+// Renders a stroked ellipse
+//
+
+//Default precision qualifier
+precision highp float;
+
+//This represents the current texture on the mesh
+uniform lowp sampler2D texture;
+
+//The interpolated texture coordinate for this fragment
+varying highp vec2 vTexCoord;
+
+//Ellipse parameters
+uniform lowp vec4 fillColor;
+uniform lowp vec4 strokeColor;
+
+uniform highp vec2 radius;
+uniform highp float strokeWidth;
+
+void main()
+{
+    highp vec2 RadiusAA = vec2(radius.x - 2.0, radius.y - 2.0);
+    
+    highp vec2 scaledPointSq = vec2( (vTexCoord.x * radius.x) *
+    (vTexCoord.x * radius.x),
+    (vTexCoord.y * radius.y) *
+    (vTexCoord.y * radius.y) );
+    
+    highp float c = (scaledPointSq.x / (radius.x*radius.x)) +
+    (scaledPointSq.y / (radius.y*radius.y));
+    
+    highp float cAA = (scaledPointSq.x / (RadiusAA.x*RadiusAA.x)) +
+    (scaledPointSq.y / (RadiusAA.y*RadiusAA.y));
+    
+    highp vec2 innerRadius = vec2( radius.x - strokeWidth * 2.0,
+    radius.y - strokeWidth * 2.0 );
+    
+    highp vec2 innerRadiusAA = vec2( radius.x - strokeWidth * 2.0 - 2.0,
+    radius.y - strokeWidth * 2.0 - 2.0 );
+    
+    highp float cInner = (scaledPointSq.x / (innerRadius.x*innerRadius.x)) +
+    (scaledPointSq.y / (innerRadius.y*innerRadius.y));
+    
+    highp float cInnerAA = (scaledPointSq.x /
+    (innerRadiusAA.x*innerRadiusAA.x)) +
+    (scaledPointSq.y /
+    (innerRadiusAA.y*innerRadiusAA.y));
+    
+    //Premult
+    lowp vec4 fragCol = mix( fillColor, strokeColor,
+    smoothstep( cInner / cInnerAA, 1.0, cInner ) );
+    
+    gl_FragColor = mix( fragCol, vec4(0,0,0,0),
+    smoothstep( c / cAA, 1.0, c ) );
+}