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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;
const float ln2 = 0.69314718055994530941723212145818;
void main (void)
{
float x = (color.r + 0.01) / 1.01;
float y = 0.0;
float z; // x-1 / x+1
int n = 50;
// ln(x) = 2[x-1 + 1 (x-1)^3 + 1 (x-1)^5 + ...] for x > 0
// [x+1 3 (x+1) 5 (x+1) ]
// Note: z will always be negative between 0.01 and 1.0 and
// so will y since it is raised to an odd power, and the shader spec
// does not support pow(-x, y) where y is not a compile time constant
z = abs((x - 1.0) / (x + 1.0));
float p = z;
for(int i = 1; i <= 101; i += 2)
{
y += p / float(i);
p *= z * z;
}
y *= -2.0 / ln2;
gl_FragColor = vec4(y / -8.0, 0.0, 0.0, 1.0);
}
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