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/*
Copyright (c) 2019 The Khronos Group Inc.
Use of this source code is governed by an MIT-style license that can be
found in the LICENSE.txt file.
*/
#ifdef GL_ES
precision mediump float;
#endif
varying vec4 color;
void main (void)
{
const float M_PI = 3.14159265358979323846;
float c = 4.0 * 2.0 * (color.r - 0.5);
float atan_c = 0.0;
float scale = 1.0;
float sign = 1.0;
vec4 result;
if(c < 0.0)
{
sign = -1.0;
c *= -1.0;
}
if(c <= 1.0)
{
// Taylors series expansion for atan
for(int i = 1; i < 12; i += 2)
{
atan_c += scale * pow(c, float(i)) / float(i);
scale *= -1.0;
}
result = vec4(sign * atan_c / M_PI + 0.5, 0.0, 0.0, 1.0);
}
else
{
c = 1.0 / c;
// Taylors series expansion for atan
for(int i = 1; i < 12; i += 2)
{
atan_c += scale * pow(c, float(i)) / float(i);
scale *= -1.0;
}
result = vec4(sign * (M_PI / 2.0 - atan_c) / M_PI + 0.5, 0.0, 0.0, 1.0);
}
gl_FragColor = result;
}
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