/*
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.
*/


attribute vec4 gtf_Vertex;
uniform mat4 gtf_ModelViewProjectionMatrix;
varying vec4 color;

#define ERROR_EPSILON 0.1

void main (void)
{
	float x;
	// Declare a 2 by 2 matrix with unique elements.
	mat2 a = mat2(1.0, 2.0,   // 1.0 4.0
	              4.0, 8.0);  // 2.0 8.0

	// Copy the matrix to another non-const matrix.
	mat2 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[1][0] != 4.0) elms = false;
	if(b[1][1] != 8.0) elms = false;

	// Add up each row of the copy.
	bool rows = true;
	x = b[0][0] + b[1][0];
	if(x < 5.0-ERROR_EPSILON || x > 5.0+ERROR_EPSILON) rows = false;
	x = b[0][1] + b[1][1];
	if(x < 10.0-ERROR_EPSILON || x > 10.0+ERROR_EPSILON) rows = false;

	// Add up each column of the copy.
	bool cols = true;
	x = b[0][0] + b[0][1];
	if(x < 3.0-ERROR_EPSILON || x > 3.0+ERROR_EPSILON) cols = false;
	x = b[1][0] + b[1][1];
	if(x < 12.0-ERROR_EPSILON || x > 12.0+ERROR_EPSILON) cols = false;

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

	// Assign the varying variable color.
	color = vec4(gray, gray, gray, 1.0);

	// Transform the vertex position.
	gl_Position = gtf_ModelViewProjectionMatrix * gtf_Vertex;
}