1 2/* 3Copyright (c) 2019 The Khronos Group Inc. 4Use of this source code is governed by an MIT-style license that can be 5found in the LICENSE.txt file. 6*/ 7 8 9#ifdef GL_ES 10#ifdef GL_FRAGMENT_PRECISION_HIGH 11precision highp float; 12#else 13precision mediump float; 14#endif 15#endif 16varying vec4 color; 17 18void main (void) 19{ 20 const float M_PI = 3.14159265358979323846; 21 float x = 2.0 * (color.g - 0.5); 22 float y = 2.0 * (color.b - 0.5); 23 float atan_c = 0.0; 24 float scale = 1.0; 25 float sign = 1.0; 26 vec4 result = vec4(0.0, 0.0, 0.0, 1.0); 27 const float epsilon = 1.0e-4; 28 29 // Avoid evaluating atan(0, x) for x < epsilon because it's implementation-dependent 30 if(x > epsilon || abs(y) > epsilon) 31 { 32 if(x < 0.0 ^^ y < 0.0) 33 { 34 sign = -1.0; 35 } 36 37 if(abs(y) <= abs(x)) 38 { 39 float c = abs(y / x); 40 41 // Taylors series expansion for atan 42 for(int i = 1; i < 12; i += 2) 43 { 44 atan_c += scale * pow(c, float(i)) / float(i); 45 scale *= -1.0; 46 } 47 48 result = vec4(sign * atan_c / (2.0 * M_PI) + 0.5, 0.0, 0.0, 1.0); 49 } 50 else 51 { 52 float c = abs(x / y); 53 54 // Taylors series expansion for atan 55 for(int i = 1; i < 12; i += 2) 56 { 57 atan_c += scale * pow(c, float(i)) / float(i); 58 scale *= -1.0; 59 } 60 61 result = vec4(sign * (M_PI / 2.0 - atan_c) / (2.0 * M_PI) + 0.5, 0.0, 0.0, 1.0); 62 } 63 64 if(x < 0.0) 65 if(y < 0.0) result.r -= 0.5; 66 else if(y > 0.0) result.r += 0.5; 67 } 68 69 gl_FragColor = result; 70} 71 72