/*
 * 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.
 */

/* normals.c - Show the effect of lighting on a flat surface
 *	when using face normals and vertex normals. The red 
 *	lines represent the directions of the normal vectors.
 *
 *	Left Mousebutton        - move eye position
 *	Middle Mousebutton      - change twist angle
 *	Right Mousebutton       - move up / down to zoom in / out
 *	Escape Key              - exit the program
 */

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

#include "3d.h"
#include <math.h>
#include <stdio.h>

/*  Function Prototypes  */

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

GLvoid  drawNormal( GLfloat, GLfloat, GLfloat, GLfloat, GLfloat, GLfloat );

void resetView( GLvoid );
void polarView( GLfloat, GLfloat, GLfloat, GLfloat );
void printHelp( char * );

/* Global Definitions */

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

/* Global Variables */

enum		actions { MOVE_EYE, TWIST_EYE, ZOOM, MOVE_NONE };
static GLint		action;

static GLdouble		xStart = 0.0, yStart = 0.0;

static GLfloat 		fovy, nearClip, farClip, distance, twistAngle, incAngle, azimAngle;

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

	glutInit( &argc, argv );

	/* create a window that is 1/4 the size of the screen */

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

	initgfx();

	glutMouseFunc( mouse );
	glutMotionFunc( motion );
	glutKeyboardFunc( keyboard );
	glutReshapeFunc( reshape );
	glutDisplayFunc( drawScene ); 

	printHelp( argv[0] );

	glutMainLoop();
}

void
printHelp( char *progname )
{
	fprintf(stdout, "\n%s - demonstrate face and vertex normals\n\n" 
		"Left Mousebutton	- move eye position\n"
		"Middle Mousebutton	- change twist angle\n"
		"Right Mousebutton	- move up / down to zoom in / out\n"
		"Escape Key		- exit the program\n\n",
		progname);
}

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

	fovy = 60.0f;	/* field of view in Y */
	nearClip = 3.0f;	/* Near clipping plane location */
	farClip  = 12.0f;	/* Far clipping plane location */

	resetView();

	/* Turn on a default light */
	glEnable( GL_LIGHT0 );
}

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

GLvoid 
mouse( GLint button, GLint state, GLint x, GLint y )
{
	static GLint buttons_down = 0;

	if (state == GLUT_DOWN) {
		switch (button) {
		case GLUT_LEFT_BUTTON:
			action = MOVE_EYE;
			break;
		case GLUT_MIDDLE_BUTTON:
			action = TWIST_EYE;
			break;
		case GLUT_RIGHT_BUTTON:
			action = ZOOM;
			break;
		}

		/* Update the saved mouse position */
		xStart = x;
		yStart = y;
	} else {
		if (--buttons_down == 0) 
			action = MOVE_NONE;
	}

}

GLvoid
motion( GLint x, GLint y )
{
	switch (action) {
	case MOVE_EYE:
		/* Adjust the eye position based on the mouse position */
		azimAngle += (GLdouble) (x - xStart);
		incAngle -= (GLdouble) (y - yStart);
		break;
	case TWIST_EYE:
		/* Adjust the eye twist based on the mouse position */
		twistAngle = fmod(twistAngle+(x - xStart), 360.0);
		break;
	case ZOOM:
		/* Adjust the eye distance based on the mouse position */
		distance -= (GLdouble) (y - yStart)/10.0;
		break;
	default:
		printf("unknown action %d\n", action);
	}
	
	/* Update the stored mouse position for later use */
	xStart = x;
	yStart = y;

	glutPostRedisplay();
}

void
resetView( GLvoid )
{
	distance = nearClip + (farClip - nearClip) / 2.0;
	twistAngle = 0.0;	/* rotation of viewing volume (camera) */
	incAngle = 60.0;
	azimAngle = 0.0;
	fovy = 60.0f;	/* Field of view in Y angle */
}

GLvoid
reshape( GLsizei width, GLsizei height )
{
	GLdouble	aspect;

	glViewport( 0, 0, width, height );

	aspect = (GLdouble) width / (GLdouble) height;

	glMatrixMode( GL_PROJECTION );
	glLoadIdentity();
	gluPerspective( fovy, aspect, nearClip, farClip );
	glMatrixMode( GL_MODELVIEW );
}

void
polarView( GLfloat distance, GLfloat azimuth, GLfloat incidence,
			GLfloat twist)
{
	glTranslatef( 0.0f, 0.0f, -distance);
	glRotatef( -twist, 0.0f, 0.0f, 1.0f);
	glRotatef( -incidence, 1.0f, 0.0f, 0.0f);
	glRotatef( -azimuth, 0.0f, 0.0f, 1.0f);
}

GLvoid
drawNormal( GLfloat px, GLfloat py, GLfloat pz,
	GLfloat nx, GLfloat ny, GLfloat nz )
{
	GLdouble normal[3], cross[3], zaxis[3];
	GLdouble angle;

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#define DegreesToRadians        (M_PI / (GLfloat) 180.0)

	glColor3f( 1.0f, 0.0f, 0.0f );
	glPushMatrix();
		glTranslatef( px, py, pz );
		glBegin( GL_LINES );
			glVertex3f( 0.0f, 0.0f, 0.0f );
			glVertex3f( nx, ny, nz );
		glEnd();

		/* normalize the normal vector */
		normal[0] = nx; normal[1] = ny; normal[2] = nz;
		normalize( normal );

		/* determine angle between z axis and normal */
		zaxis[0] = 0; zaxis[1] = 0; zaxis[2] = 1;
		angle = acos( dot3( zaxis, normal ) )/DegreesToRadians;
		
		if ( angle != 0.0 ) {
			/* find the axis of rotation */
			crossprod( zaxis, normal, cross );
			glRotatef( angle, cross[0], cross[1], cross[2] );
		}
		/* move to end of normal vector */
		glTranslatef( 0.0f, 0.0f, 1.0f );
		glutSolidCone( 0.05, 0.1, 8, 8 );
	glPopMatrix();
}

GLvoid
drawScene( GLvoid )
{
	glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

	glPushMatrix();

		polarView( distance, azimAngle, incAngle, twistAngle );

		/* Draw a lit flat-shaded triangle on the left */
		glPushMatrix();
			glTranslatef( -2.0f, 0.0f, 0.0f );

			/* Turn on lighting computations */
			glEnable( GL_LIGHTING );

			glBegin( GL_TRIANGLES );
				glNormal3f( 0.0f, 0.0f, 1.0f );
				glVertex2f( 0.0f, 1.0f );
				glVertex2f( -0.866f, -0.50f );
				glVertex2f( 0.866f, -0.50f );
			glEnd();

			/* Turn off lighting computations */
			glDisable( GL_LIGHTING );
			
			/* Draw an unlit line representing the face normal */
			drawNormal( 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f );
		glPopMatrix();

		/* Draw a lit, smooth-shaded triangle on the right */
		glPushMatrix();
			glTranslatef( 2.0f, 0.0f, 0.0f );

			/* Turn on lighting computations */
			glEnable( GL_LIGHTING );

			glBegin( GL_TRIANGLES );
				glNormal3f( 0.0f, 0.0f, 1.0f );
				glVertex2f( 0.0f, 1.0f );
				glNormal3f( 0.455f, 0.796f, 0.398f );
				glVertex2f( -0.866f, -0.50f );
				glNormal3f( 0.162f, 0.566f, 0.808f );
				glVertex2f( 0.866f, -0.50f );
			glEnd();

			/* Turn off lighting computations */
			glDisable( GL_LIGHTING );

			/* Draw unlit lines representing the vertex normals */
			drawNormal( 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 1.0f );
			drawNormal( -0.866f, -0.50f, 0.0f, 0.455f, 0.796f, 0.398f );
			drawNormal( 0.866f, -0.50f, 0.0f, 0.162f, 0.566f, 0.808f );
		glPopMatrix();


	glPopMatrix();

	glutSwapBuffers();
}