Open source Star Ruler 2 source code!

data/shaders/source/radial_progress_ps.txt

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+#define pi 3.141592653589793238462643383279
+#define twopi (pi * 2.0)
+varying vec2 rcoords;
+uniform float progress;
+
+const float maxRad = 0.8;
+const float minRad = 0.4;
+
+void main() {
+	float r = length(rcoords);
+	if(r < minRad || r > maxRad)
+		discard;
+	float ang = (atan(rcoords.y, rcoords.x) + pi) / twopi;
+	if(ang > progress)
+		discard;
+
+	float alpha = abs(r - (minRad + (maxRad - minRad) / 2.0));
+	alpha /= (maxRad - minRad);
+	alpha = 1.0 - alpha;
+	gl_FragColor.rgb = gl_Color.rgb;
+	gl_FragColor.a = alpha;
+}