data/shaders/conical_gradient.frag

0001 /*
0002  *  SPDX-FileCopyrightText: 2007 Adrian Page <adrian@pagenet.plus.com>
0003  *
0004  *  SPDX-License-Identifier: GPL-2.0-or-later
0005  */
0006
0007 uniform sampler1D gradientColors;
0008
0009 uniform vec2 gradientVectorStart;
0010 uniform float gradientVectorAngle;
0011
0012 const float PI = 3.1415926535;
0013
0014 void main(void)
0015 {
0016     vec2 p = gl_TexCoord[0].st - gradientVectorStart;
0017
0018     float angle = atan(p.y, p.x) + PI;
0019     angle -= gradientVectorAngle;
0020
0021     if (angle < 0.0) {
0022         angle += 2.0 * PI;
0023     }
0024
0025     float t = angle / (2.0 * PI);
0026
0027     gl_FragColor = texture1D(gradientColors, t);
0028 }