
/*
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

/* 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)
{
	float x;
	// Declare a constant 4 by 4 matrix with unique elements.
	const mat4 a = mat4( 1.0,  2.0,  3.0,  4.0,
	                     5.0,  6.0,  7.0,  8.0,
	                     9.0, 10.0, 11.0, 12.0,
	                    13.0, 14.0, 15.0, 16.0);

	// Copy the constant matrix to another non-const matrix.
	mat4 b = a;

	// Check each element of the copy.
	bool elms = true;
	if(b[0][0] !=  1.0) elms = false;
	if(b[0][1] !=  2.0) elms = false;
	if(b[0][2] !=  3.0) elms = false;
	if(b[0][3] !=  4.0) elms = false;
	if(b[1][0] !=  5.0) elms = false;
	if(b[1][1] !=  6.0) elms = false;
	if(b[1][2] !=  7.0) elms = false;
	if(b[1][3] !=  8.0) elms = false;
	if(b[2][0] !=  9.0) elms = false;
	if(b[2][1] != 10.0) elms = false;
	if(b[2][2] != 11.0) elms = false;
	if(b[2][3] != 12.0) elms = false;
	if(b[3][0] != 13.0) elms = false;
	if(b[3][1] != 14.0) elms = false;
	if(b[3][2] != 15.0) elms = false;
	if(b[3][3] != 16.0) elms = false;

	// Add up each row of the copy.
	bool rows = true;
	x = b[0][0] + b[1][0] + b[2][0] + b[3][0];
	if(x < 28.0-ERROR_EPSILON || x > 28.0+ERROR_EPSILON) rows = false;
	x = b[0][1] + b[1][1] + b[2][1] + b[3][1];
	if(x < 32.0-ERROR_EPSILON || x > 32.0+ERROR_EPSILON) rows = false;
	x = b[0][2] + b[1][2] + b[2][2] + b[3][2];
	if(x < 36.0-ERROR_EPSILON || x > 36.0+ERROR_EPSILON) rows = false;
	x = b[0][3] + b[1][3] + b[2][3] + b[3][3];
	if(x < 40.0-ERROR_EPSILON || x > 40.0+ERROR_EPSILON) rows = false;

	// Add up each column of the copy.
	bool cols = true;
	x = b[0][0] + b[0][1] + b[0][2] + b[0][3];
	if(x < 10.0-ERROR_EPSILON || x > 10.0+ERROR_EPSILON) cols = false;
	x = b[1][0] + b[1][1] + b[1][2] + b[1][3];
	if(x < 26.0-ERROR_EPSILON || x > 26.0+ERROR_EPSILON) cols = false;
	x = b[2][0] + b[2][1] + b[2][2] + b[2][3];
	if(x < 42.0-ERROR_EPSILON || x > 42.0+ERROR_EPSILON) cols = false;
	x = b[3][0] + b[3][1] + b[3][2] + b[3][3];
	if(x < 58.0-ERROR_EPSILON || x > 58.0+ERROR_EPSILON) cols = false;

	// Check if all of the operations were successful.
	float gray = elms && rows && cols ? 1.0 : 0.0;

	// Assign the fragment color.
	gl_FragColor = vec4(gray, gray, gray, 1.0);
}

