
/*
** Copyright (c) 2012 The Khronos Group Inc.
**
** Permission is hereby granted, free of charge, to any person obtaining a
** copy of this software and/or associated documentation files (the
** "Materials"), to deal in the Materials without restriction, including
** without limitation the rights to use, copy, modify, merge, publish,
** distribute, sublicense, and/or sell copies of the Materials, and to
** permit persons to whom the Materials are furnished to do so, subject to
** the following conditions:
**
** The above copyright notice and this permission notice shall be included
** in all copies or substantial portions of the Materials.
**
** THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
** MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
*/


attribute vec4 gtf_Color;
attribute vec4 gtf_Vertex;
uniform mat4 gtf_ModelViewProjectionMatrix;
varying vec4 color;

void main (void)
{
    vec3 x = (gtf_Color.rgb + 0.01) / 1.01;
    vec3 y = vec3(0.0);
    vec3 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));
    vec3 p = z;
    for(int i = 1; i <= 101; i += 2)
    {
        y += p / float(i);
        p *= z * z;
    }
    y *= -2.0;

    color = vec4(y / -4.61, 1.0);
    gl_Position = gtf_ModelViewProjectionMatrix * gtf_Vertex;
}
