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#ifdef GL_OES_standard_derivatives
#extension GL_OES_standard_derivatives : enable
// else we probably have fwidth() in core
#endif

varying lowp vec3 edgeColor;
varying lowp vec3 color;
varying lowp vec2 barycentric;

lowp vec4 zero = vec4(0.0);
void main()
{
    lowp vec2 d = fwidth(barycentric) * 5.0;
    lowp vec4 edge_closeness = smoothstep(zero, vec4(d.x, d.y, d.x, d.y),
            vec4(barycentric.x, barycentric.y, 1.0 - barycentric.x, 1.0 - barycentric.y));
    lowp float total = min(min(edge_closeness[0], edge_closeness[1]),
            min(edge_closeness[2], edge_closeness[3]));
    // square to make lines sharper
    total = total > 0.5 ? (1.0 - (1.0 - total) * (1.0 - total) * 2.0) : total * total * 2.0;
    gl_FragColor.rgb = mix(edgeColor, color, total);
}
