/* picking.c */

/*
	Purpose : view vectors & create normals
*/


#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define KEY_ESC 27


/*
	New types
*/

typedef struct ViewInfo ViewInfo;
struct ViewInfo
{
	GLfloat radius;
	GLfloat angle;
	GLfloat elevation;
};


/*
	Module level variables and constants
*/

static const int mMaxSize = 3;

static ViewInfo mViewInfo = {	1.5,	/* radius */
								0.0,	/* angle */
								0.0,	/* elevation */
};



/*
	Functions
*/

GLvoid checkError( const char* const label )
{
	GLenum error;

	error = glGetError();
	while ( GL_NO_ERROR != error )
	{
		fprintf( stderr,"%s: %s\n", label, (char*) gluErrorString(error) );
		error = glGetError();
	}
}


void reshape( GLint width, GLint height )
{
	/* We still want the output to cover the whole window */
	glViewport( 0, 0, width, height );

	glMatrixMode( GL_PROJECTION );
	glLoadIdentity();
	glOrtho( -mMaxSize, mMaxSize,  -mMaxSize, mMaxSize,  -mMaxSize, mMaxSize );
	glMatrixMode( GL_MODELVIEW );
}


GLvoid keyboard( GLubyte key, GLint x, GLint y)
{
	switch (key)
	{
  	case KEY_ESC:   /* exit when escape key is pressed */
		exit(0);
	break;

	case 'a':
	case 'A':
		mViewInfo.elevation += 2.0;
	break;

	case 'z':
	case 'Z':
		mViewInfo.elevation -= 2.0;
	break;

	}

	glutPostRedisplay();
}


void specialkeys( GLint key, GLint xpos, GLint ypos )
{
    switch( key )
	{
	case GLUT_KEY_LEFT: /* move left */
		mViewInfo.angle += 2.0;
	break;

	case GLUT_KEY_RIGHT: /* move left */
		mViewInfo.angle -= 2.0;

	break;

	}

	glutPostRedisplay();
}


/* Make a graphical representation of a vector */
void drawVec( const float vec[3] )
{
	glBegin( GL_LINES );
		glVertex3f( 0.0, 0.0, 0.0 );
		glVertex3fv( vec );
	glEnd();
}

/*
	retVec = v1 x v2
	Caller is responsible for allocation retVec space.
*/
void crossProduct( float retVec[3], const float v1[3], const float v2[3])
{
	retVec[0] = v1[1]*v2[2] - v1[2]*v2[1];
	retVec[1] = v1[2]*v2[0] - v1[0]*v2[2];
	retVec[2] = v1[0]*v2[1] - v1[1]*v2[0];
}


/*
	Take a c-string and display it at raster location (x,y,z)
*/
void displayStr(const char* const str, const GLfloat x, const GLfloat y, const GLfloat z)
{
	/* choose what font we wish to use */
	void* fontName = GLUT_BITMAP_HELVETICA_18;

	unsigned int index = 0;

	/* where do we want the text to go */
	glRasterPos3f(x, y, z);

	/* Display the string on the screen */
	while( str[index] != 0  &&  index < 1000 )
	{
		if( '\t' != str[index] )
		{
			glutBitmapCharacter( fontName, str[index] );
		}
		else
		{
			int loop;
			for( loop = 0; loop < 8; ++loop ) glutBitmapCharacter( fontName, ' ' );
		}
		++index;
	}

}


void drawAxes( void )
{
	glColor3f( 0.0, 0.0, 1.0 );
	glBegin( GL_LINES );
		glVertex3f( 0.0, 0.0, 0.0 );
		glVertex3f( 1.0, 0.0, 0.0 );

		glVertex3f( 0.0, 0.0, 0.0 );
		glVertex3f( 0.0, 1.0, 0.0 );

		glVertex3f( 0.0, 0.0, 0.0 );
		glVertex3f( 0.0, 0.0, 1.0 );		
	glEnd();
	
	displayStr( "x", 1.2, 0.0, 0.0 );
	displayStr( "y", 0.0, 1.2, 0.0 );
	displayStr( "z", 0.0, 0.0, 1.2 );
}
/*
	Draw a simple scene with three objects.
*/
void drawScene( void )
{
	glLoadIdentity();   /* Reset the ModelView transformation every time we draw */

	/* set up viewing position */
	glTranslatef( 0, 0, -mViewInfo.radius );
	glRotatef( mViewInfo.elevation, 1, 0, 0 );
	glRotatef( mViewInfo.angle, 0, 1, 0 );

	drawAxes();

	/* draw here */
	{
		float v1[3] = { 1.0, 0.0, 1.0 };
		float v2[3] = { 1.0, 1.0, 0.0 };
		float normal[3];

		glColor3f( 0.0, 1.0, 1.0 );
		drawVec( v1 );
		drawVec( v2 );

		glColor3f( 1.0, 0.0, 0.0 );
		crossProduct( normal, v1, v2 );		
		drawVec( normal );
	}
}


GLvoid display( GLvoid )
{
	/* Do all your OpenGL rendering here */

	glClear( GL_COLOR_BUFFER_BIT );

	/* Draw some objects for picking */
	drawScene();

	/*
		Don't check errors every frame - expensive. Only do it
		while debugging.
	*/
	checkError( "display" );

	glFlush();
}

void init( void )
{
	glClearColor( 0.0, 0.0, 0.0, 1.0 );
	glLineWidth( 3.0 );
}


int main( int argc, char* argv[] )
{
	glutInit( &argc, argv );
	glutInitDisplayMode( GLUT_RGBA );
	glutCreateWindow( argv[0] );

	glutDisplayFunc( display );
	glutKeyboardFunc( keyboard );
	glutReshapeFunc( reshape );
	glutSpecialFunc( specialkeys );

	init();

	glutMainLoop();

	return 0;
}