/*
 * 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.
 */

/*  grid.c  - open a window, clear the background, and render a
 *       grid of points or lines centered around the origin.
 *
 *	SPACE key	- toggle between point/line grid
 *	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 */

static GLint pointGrid = GL_TRUE;

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 - demonstrates simple rendering primitives\n\n"
		"SPACE Key		- toggle between point/line grid\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 ' ':
		pointGrid = !pointGrid;
		glutPostRedisplay();
		break;
	case KEY_ESC:	/* Exit whenever the Escape key is pressed */
		exit(0);
	}
}

GLvoid
drawScene( GLvoid )
{
	GLfloat x, y;

	glClear( GL_COLOR_BUFFER_BIT );

	glColor3f( 1.0f, 1.0f, 1.0f );

	if (pointGrid) {
		/* Render a grid composed of evenly spaced points */
		glPointSize( 3.5 ); 
		glBegin( GL_POINTS );
		for ( x = -1.0f; x < 1.1f; x += 0.1f ) 
			for ( y = -1.0f; y < 1.1f; y += 0.1f )
				glVertex2f( x, y );
		glEnd();
	} else {
		/* Draw a line grid centered at the origin */
		glLineWidth( 2.5 );
		glBegin( GL_LINES );
		for ( x = -1.0f; x < 1.1f; x += 0.1f ) {/* draw vertical lines */
			glVertex2f( x, -1.0f );
			glVertex2f( x, 1.0f );
		}
		for ( y = -1.0f; y < 1.1f; y += 0.1f ) {/* draw horizontal lines */
			glVertex2f( -1.0f, y );
			glVertex2f( 1.0f, y );
		}
		glEnd();
	}

	glFlush();
}