/*
 * 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.
 */

/*  shadeModel.c  - open a window, clear the background, and render a 
 *	line, a triangle fan and a quad strip using flat/smooth shading.
 *
 *	SPACE key	- toggle between flat/smooth shading
 *	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 flatShading = GL_FALSE;

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 shading models\n\n"
		"SPACE Key		- toggle between flat/smooth shading\n"
		"Escape Key		- exit the program\n\n",
		progname);
}

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

	glOrtho( 0.0, 1.0, 0.0, 1.0, -1.0, 1.0 );
}

GLvoid 
keyboard( GLubyte key, GLint x, GLint y )
{
    static GLboolean flat = GL_FALSE;
    
	switch (key) {
	case ' ':
		flatShading = !flatShading;
		if (flatShading) 
			glShadeModel(GL_FLAT);
		else
			glShadeModel(GL_SMOOTH);
		glutPostRedisplay();
		break;
	case KEY_ESC:	/* Exit whenever the Escape key is pressed */
		exit(0);
	}
}

GLvoid
drawScene( GLvoid )
{
	static GLfloat    blackColor[] = { 0.0f, 0.0f, 0.0f };
	static GLfloat    redColor[]  = { 1.0f, 0.0f, 0.0f };
	static GLfloat    purpleColor[] = { 1.0f, 0.0f, 1.0f };
	static GLfloat    yellowColor[] = { 1.0f, 1.0f, 0.0f };
	static GLfloat    whiteColor[] = { 1.0f, 1.0f, 1.0f };
	static GLfloat    darkgreenColor[] = { 0.0f, 0.5f, 0.0f };
	
	glClear( GL_COLOR_BUFFER_BIT );

	/* Draw a point */
	glBegin( GL_POINTS );
	  glColor3fv( whiteColor );
	  glVertex2f( 0.3f, 0.85f );
	  glColor3f( 1.0f, 0.50f, 0.0f );   /* Orange */
	  glVertex2f( 3.0f, 9.65f );       /* This point is clipped */
	glEnd();

	/* Gouraud shade a line */
	glBegin( GL_LINES );
	  glColor3f( 1.0f, 0.0f, 0.0f );    /* Red */
	  glVertex2f( 0.1f, 0.1f );
	  glColor3fv( yellowColor );
	  glVertex2f( 0.2f, 0.9f );
	glEnd();

	/* Gouraud shade a polygon */
	glBegin( GL_POLYGON );
	  glColor3fv( purpleColor );
	  glVertex2f( 0.5f, 0.1f );
	  glColor3fv( redColor );
	  glVertex2f( 1.0f, 0.4f );
	  glColor3fv( blackColor );
	  glVertex2f( 0.9f, 1.0f );
	  glColor3fv( darkgreenColor );
	  glVertex2f( 0.3f, 0.8f );
	  glColor3fv( whiteColor );
	  glVertex2f( 0.1f, 0.5f );
	glEnd();

	/* Draw a triangle fan */
	glBegin( GL_TRIANGLE_FAN );
	  glColor3fv( blackColor );
	  glVertex2f( 0.4f, 0.4f );
	  glColor3fv( redColor );
	  glVertex2f( 0.3f, 0.4f );
	  glColor3f( 0.0f, 0.0f, 1.0f );	/* blue */
	  glVertex2f( 0.4f, 0.5f );
	  glColor3fv( yellowColor );
	  glVertex2f( 0.5f, 0.5f );
	  glColor3fv( whiteColor );
	  glVertex2f( 0.5f, 0.4f );
	  glColor3fv( darkgreenColor );
	  glVertex2f( 0.4f, 0.3f );
	glEnd();

	glFlush();
}