/*
 * 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.
 */

/* viewport.c - Demonstrates how to separate a window into two drawing 
 *	areas using glViewport().  It creates two viewports that divide 
 *	the window in half. In each half, a rectangle the size of the 
 *	viewing volume is rendered. In one half it also renders a square 
 *	grid. Note how the mapping of the viewing volume to the viewport
 *	affects the shape of the grid.
 *
 *	SPACE key	- toggle which viewport the grid is drawn in
 *	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 );

void printHelp( char * );

/* Global Definitions */

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

/* Global Variables */

static	GLboolean	grid_in_bottom = GL_TRUE;

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();

	glutKeyboardFunc( keyboard );
	glutDisplayFunc( drawScene ); 

	printHelp( argv[0] );

	glMatrixMode( GL_PROJECTION );
	glOrtho( -2.0, 2.0, -2.0, 2.0, -1.0, 1.0 );
	glMatrixMode( GL_MODELVIEW );

	glutMainLoop();
}

void
printHelp( char *progname )
{
	fprintf(stdout, "\n%s - demonstrates how the viewport controls \n"
		"what portion of the window will be rendered into\n\n"
		"SPACE key		- toggle which viewport the grid is drawn in\n"
		"Escape Key		- exit the program\n\n",
		progname);
}

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

GLvoid 
keyboard( GLubyte key, GLint x, GLint y )
{
	switch (key) {
	case ' ':	/* toggle grid location */
		grid_in_bottom = !grid_in_bottom;
		glutPostRedisplay();
		break;
	case KEY_ESC:	/* Exit when the Escape key is pressed */
		exit(0);
	}
}

/* Draw a square grid */
GLvoid
drawSquareGrid( GLvoid )
{
	GLfloat		x, y;

	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();
}


GLvoid
drawScene( GLvoid )
{
	GLsizei		width, height;

	static GLfloat  blueColor[] = { 0.0f, 0.0f, 1.0f };
	static GLfloat  greenColor[] = { 0.0f, 1.0f, 0.0f };

	glClear( GL_COLOR_BUFFER_BIT );

	/* Get the current window size */
	width = glutGet(GLUT_WINDOW_WIDTH); 
	height = glutGet(GLUT_WINDOW_HEIGHT);

	/* Create the first viewport - the bottom half of the screen */
	glViewport( 0, 0, width, height / 2 );

	/* Draw a blue rectangle that fills the entire viewing volume */
	glColor3fv( blueColor );
	glRectf( -2.0f, -2.0f, 2.0f, 2.0f );

	if (grid_in_bottom) {
		glColor3f( 1.0f, 1.0f, 1.0f );
		drawSquareGrid();
	}

	/* Create the second viewport - the top half of the screen */
	glViewport( 0, height / 2, width, height / 2 );

	/* Draw a green rectangle that fills the entire viewing volume */
	glColor3fv( greenColor );
	glRectf( -2.0f, -2.0f, 2.0f, 2.0f );

	if (!grid_in_bottom) {
		glColor3f( 0.0f, 0.0f, 0.0f );
		drawSquareGrid();
	}

	glFlush();
}