/*
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 3 by 3 matrix with unique elements.
	const mat3 a = mat3( 1.0, 2.0, 3.0,
	                     4.0, 5.0, 6.0,
	                     7.0, 8.0, 9.0);

	// Copy the constant matrix to another non-const matrix.
	mat3 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[1][0] != 4.0) elms = false;
	if(b[1][1] != 5.0) elms = false;
	if(b[1][2] != 6.0) elms = false;
	if(b[2][0] != 7.0) elms = false;
	if(b[2][1] != 8.0) elms = false;
	if(b[2][2] != 9.0) elms = false;

	// Add up each row of the copy.
	bool rows = true;
	x = b[0][0] + b[1][0] + b[2][0];
	if( x < 12.0-ERROR_EPSILON || x > 12.0+ERROR_EPSILON ) rows = false;
	x = b[0][1] + b[1][1] + b[2][1];
	if(x < 15.0-ERROR_EPSILON || x > 15.0+ERROR_EPSILON ) rows = false;
	x = b[0][2] + b[1][2] + b[2][2];
	if(x < 18.0-ERROR_EPSILON || x > 18.0+ERROR_EPSILON ) rows = false;

	// Add up each column of the copy.
	bool cols = true;
	x = b[0][0] + b[0][1] + b[0][2];
	if( x < 6.0-ERROR_EPSILON || x > 6.0+ERROR_EPSILON ) cols = false;
	x = b[1][0] + b[1][1] + b[1][2];
	if(x < 15.0-ERROR_EPSILON || x > 15.0+ERROR_EPSILON) cols = false;
	x = b[2][0] + b[2][1] + b[2][2];
	if(x < 24.0-ERROR_EPSILON || x > 24.0+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);
}