/*
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;

/* This epsilon will work as long as the magnitude of the float is < 128.
 * This can be seen by taking the spec relative mediump precision of 2^-10:
 * 0.125 / 2^-10 = 128
 */
#define ERROR_EPSILON (0.125)

void main (void)
{
	vec4 L1 = vec4(1.0, 2.0, 3.0, 4.0);
	vec4 L2 = vec4(5.0, 6.0, 7.0, 8.0);
	vec4 L3 = vec4(9.0, 10.0, 11.0, 12.0);
	vec4 L4 = vec4(13.0, 14.0, 15.0, 16.0);

	mat4 a = mat4(L1,L2,L3,L4);

	float gray,sum1=0.0,sum2=0.0,sum3=0.0,sum4=0.0;
	int i;

	sum1 = sum1 + a[0][0];
	sum2 = sum2 + a[1][0];
	sum3 = sum3 + a[2][0];
	sum4 = sum4 + a[3][0];

	sum1 = sum1 + a[0][1];
	sum2 = sum2 + a[1][1];
	sum3 = sum3 + a[2][1];
	sum4 = sum4 + a[3][1];

	sum1 = sum1 + a[0][2];
	sum2 = sum2 + a[1][2];
	sum3 = sum3 + a[2][2];
	sum4 = sum4 + a[3][2];

	sum1 = sum1 + a[0][3];
	sum2 = sum2 + a[1][3];
	sum3 = sum3 + a[2][3];
	sum4 = sum4 + a[3][3];

	if( ( sum1 > 10.0-ERROR_EPSILON && sum1 < 10.0+ERROR_EPSILON  ) &&
		( sum2 > 26.0-ERROR_EPSILON && sum2 < 26.0+ERROR_EPSILON) &&
		( sum3 > 42.0-ERROR_EPSILON && sum3 < 42.0+ERROR_EPSILON) &&
		( sum4 > 58.0-ERROR_EPSILON && sum4 < 58.0+ERROR_EPSILON) )
	gray=1.0;
	else gray=0.0;
	gl_FragColor = vec4(gray, gray, gray, 1.0);
}