/*
 * 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.
 */

/* aspect.c - draw a grid, using glutReshapeFunc() to handle
 *	window resizes (taking into account the aspect ratio).
 *
 *	Escape Key	- exit program
 */
#include <GL/glut.h>	/* includes gl.h, glu.h */

#include <stdio.h>

/*  Function Prototypes  */

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

void printHelp( char * );

/* Global Definitions */

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

GLvoid
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();

	glutReshapeFunc( reshape );
	glutKeyboardFunc( keyboard );
	glutDisplayFunc( drawScene ); 

	printHelp( argv[0] );

	glutMainLoop();
}

void
printHelp( char *progname )
{
	fprintf(stdout, "\n%s - demonstrates one way to make the aspect "
		"ratio of the viewport\nand the viewing volume match\n\n"
		"Escape Key		- exit the program\n\n",
		progname);
}

GLvoid
initgfx( GLvoid )
{
	glClearColor( 0.0, 0.0, 1.0, 1.0 );
	glShadeModel( GL_FLAT );
}

GLvoid
reshape( GLsizei width, GLsizei height )
{
	GLdouble    aspect, left, right, bottom, top;

	glViewport( 0, 0, width, height );

	/* compute aspect ratio */
	aspect = (GLdouble) width / (GLdouble) height;

	/* make sure the window goes from [-2.0, 2.0] in the
	   smallest dimension */
	if ( aspect < 1.0 ) {
		left = -2.0;
		right = 2.0;
		bottom = -2.0 * ( 1.0 / aspect );
		top = 2.0 * ( 1.0 / aspect );
	} else {
		left = -2.0 * aspect;
		right = 2.0 * aspect;
		bottom = -2.0;
		top = 2.0;
	}

	glMatrixMode( GL_PROJECTION );
	/* Reset world coordinates first ... */
	glLoadIdentity();

	/* Then set them to what we want based on the new aspect ratio */
	glOrtho( left, right, bottom, top, -1.0, 1.0 );
	glMatrixMode( GL_MODELVIEW );
}

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    whiteColor[] = { 1.0, 1.0, 1.0 };

	glClear( GL_COLOR_BUFFER_BIT );

	glColor3fv( whiteColor );	

	glBegin( GL_LINES );
	for ( x = -1.0f; x < 1.1f; x += 0.1f ) {
		glVertex2f( x, -1.0f );
		glVertex2f( x, 1.0f );
	}
	for ( y = -1.0f; y < 1.1f; y += 0.1f ) {
		glVertex2f( -1.0f, y );
		glVertex2f( 1.0f, y );
	}
	glEnd();

	glFlush();
}