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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
#extension GL_OES_standard_derivatives : enable
precision mediump float;
#endif
// setting a boundary for cases where screen sizes may exceed the precision
// of the arithmetic used.
#define SAFETY_BOUND 500.0
// Macro to scale/bias the range of output. If input is [-1.0, 1.0], maps to [0.5, 1.0]..
// Accounts for precision errors magnified by derivative operation.
#define REDUCE_RANGE(A) ((A) + 3.0) / 4.0
// This fragment shader computes an image representation of the derivative of
// sine. The derivative of sine is cosine. This shader's output is compared to
// the reference shader that computes an image representation of cosine
// directly.
uniform float viewportwidth;
uniform float viewportheight;
varying vec2 vertXY;
void main (void)
{
const float M_PI = 3.14159265358979323846;
float sine;
float cosine;
#ifdef GL_OES_standard_derivatives
sine = sin(fract(gl_FragCoord.y / 128.0) * (2.0 * M_PI));
cosine = REDUCE_RANGE((128.0 / (2.0 * M_PI)) * dFdy(sine));
#else
cosine = 0.5;
#endif
if( gl_FragCoord.y < SAFETY_BOUND )
{
gl_FragColor = vec4(cosine, cosine, cosine, 1.0);
}
else discard;
}
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