/*
 * Copyright (c) 1996-1999  Silicon Graphics, Inc.  All rights reserved.
 *
 * THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
 * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
 *
 * IN NO EVENT SHALL SILICON GRAPHICS BE LIABLE FOR ANY SPECIAL, INCIDENTAL,
 * INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY DAMAGES WHATSOEVER
 * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER OR NOT ADVISED OF THE
 * POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF LIABILITY, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/*  checkerboard.c  - open a window, clear the background, and 
 *	render a checkerboard composed of flat shaded rectangles.
 *
 *	Escape key	- exit program
 */

#include <GL/glut.h>	/* includes gl.h, glu.h */
#include <stdlib.h>
#include <stdio.h>

/*  Function Prototypes  */

GLvoid  initgfx( GLvoid );
GLvoid	keyboard( GLubyte, GLint, GLint );
GLvoid  drawScene( GLvoid );

void printHelp( char * );

/* Global Definitions */

#define KEY_ESC	27	/* ascii value for the escape key */

void
main( int argc, char *argv[] )
{
	GLsizei width, height;

	glutInit( &argc, argv );

	width = glutGet( GLUT_SCREEN_WIDTH ); 
	height = glutGet( GLUT_SCREEN_HEIGHT );
	glutInitWindowPosition( width / 4, height / 4 );
	glutInitWindowSize( width / 2, height / 2 );
	glutInitDisplayMode( GLUT_RGBA );
	glutCreateWindow( argv[0] );

	initgfx();

	glutKeyboardFunc( keyboard );
	glutDisplayFunc( drawScene ); 

	printHelp( argv[0] );

	glutMainLoop();
}

void
printHelp( char *progname )
{
	fprintf(stdout, "\n%s - renders a checkerboard\n\n"
		"Escape Key		- exit the program\n\n",
		progname);
}

GLvoid
initgfx( GLvoid )
{
	glClearColor( 0.0, 0.0, 1.0, 1.0 );

	glOrtho( -2.0, 2.0, -2.0, 2.0, -1.0, 1.0 );
}

GLvoid 
keyboard( GLubyte key, GLint x, GLint y )
{
	switch (key) {
	case KEY_ESC:	/* Exit whenever the Escape key is pressed */
		exit(0);
	}
}

GLvoid
drawScene( GLvoid )
{
	GLfloat		x, y;

	static GLfloat	redColor[] = { 1.0f, 0.0f, 0.0f };
	static GLfloat	blackColor[] = { 0.0f, 0.0f, 0.0f };

	/* alternate between red and black rectangles*/
	GLboolean	useRed = GL_TRUE;  

	glClear( GL_COLOR_BUFFER_BIT );

	/* Draw a checkerboard composed of 0.1 by 0.1 rectangles 
	 * (For convenience, this code as been added to the class 
	 * library as Checkerboard()).
	 */

	for ( x = -1.0f; x < 1.0f; x += 0.1f ) {
		useRed = !useRed;
		for ( y = -1.0f; y < 1.0f; y += 0.1f ) {
			if ( useRed )
				glColor3fv( redColor );
			else
				glColor3fv( blackColor );
			glRectf( x, y, x + 0.1f, y + 0.1f );
			useRed = !useRed;
		}
	}

	glFlush();
}