/* trackball.c    */

/* E. Angel, Interactive Computer Graphics */
/* A Top-Down Approach with OpenGL, Third Edition */
/* Addison-Wesley Longman, 2003 */
/* Rotating cube demo with trackball*/#include <math.h>#include <GL/glut.h>#define bool int#define false 0#define true 1
#define M_PI 3.14159int 	winWidth, winHeight;float 	angle = 0.0, axis[3], trans[3];bool 	trackingMouse = false;bool 	redrawContinue = false;bool    trackballMove = false;/*----------------------------------------------------------------------*//*** Draw the cube.*/GLfloat vertices[][3] = {    {-1.0,-1.0,-1.0},{1.0,-1.0,-1.0}, {1.0,1.0,-1.0}, {-1.0,1.0,-1.0},     {-1.0,-1.0,1.0}, {1.0,-1.0,1.0}, {1.0,1.0,1.0}, {-1.0,1.0,1.0}};GLfloat colors[][3] = {    {0.0,0.0,0.0},{1.0,0.0,0.0}, {1.0,1.0,0.0}, {0.0,1.0,0.0},     {0.0,0.0,1.0}, {1.0,0.0,1.0}, {1.0,1.0,1.0}, {0.0,1.0,1.0}};void polygon(int a, int b, int c , int d, int face){    /* draw a polygon via list of vertices */    glBegin(GL_POLYGON);  	glColor3fv(colors[a]);  	glVertex3fv(vertices[a]);  	glColor3fv(colors[b]);  	glVertex3fv(vertices[b]);  	glColor3fv(colors[c]);  	glVertex3fv(vertices[c]);  	glColor3fv(colors[d]);  	glVertex3fv(vertices[d]);    glEnd();}void colorcube(void){    /* map vertices to faces */    polygon(1,0,3,2,0);    polygon(3,7,6,2,1);    polygon(7,3,0,4,2);    polygon(2,6,5,1,3);    polygon(4,5,6,7,4);    polygon(5,4,0,1,5);}/*----------------------------------------------------------------------*//* ** These functions implement a simple trackball-like motion control.*/float lastPos[3] = {0.0F, 0.0F, 0.0F};int curx, cury;int startX, startY;voidtrackball_ptov(int x, int y, int width, int height, float v[3]){    float d, a;    /* project x,y onto a hemi-sphere centered within width, height */    v[0] = (2.0F*x - width) / width;    v[1] = (height - 2.0F*y) / height;    d = (float) sqrt(v[0]*v[0] + v[1]*v[1]);    v[2] = (float) cos((M_PI/2.0F) * ((d < 1.0F) ? d : 1.0F));    a = 1.0F / (float) sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);    v[0] *= a;    v[1] *= a;    v[2] *= a;}voidmouseMotion(int x, int y){    float curPos[3], dx, dy, dz;    trackball_ptov(x, y, winWidth, winHeight, curPos);if(trackingMouse){    dx = curPos[0] - lastPos[0];    dy = curPos[1] - lastPos[1];    dz = curPos[2] - lastPos[2];    if (dx || dy || dz) {	angle = 90.0F * sqrt(dx*dx + dy*dy + dz*dz);	axis[0] = lastPos[1]*curPos[2] - lastPos[2]*curPos[1];	axis[1] = lastPos[2]*curPos[0] - lastPos[0]*curPos[2];	axis[2] = lastPos[0]*curPos[1] - lastPos[1]*curPos[0];	lastPos[0] = curPos[0];	lastPos[1] = curPos[1];	lastPos[2] = curPos[2];    }}     glutPostRedisplay();}voidstartMotion(int x, int y){    trackingMouse = true;    redrawContinue = false;    startX = x; startY = y;    curx = x; cury = y;    trackball_ptov(x, y, winWidth, winHeight, lastPos);	trackballMove=true;}voidstopMotion(int x, int y){    trackingMouse = false;    if (startX != x || startY != y) {	redrawContinue = true;    } else {	angle = 0.0F;	redrawContinue = false;	trackballMove = false;    }}/*----------------------------------------------------------------------*/void display(void){    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);    /* view transform */    if (trackballMove) {	    glRotatef(angle, axis[0], axis[1], axis[2]);    }	colorcube();    glutSwapBuffers();}/*----------------------------------------------------------------------*/void mouseButton(int button, int state, int x, int y){	if(button==GLUT_RIGHT_BUTTON) exit(0);	if(button==GLUT_LEFT_BUTTON) switch(state) 	{    case GLUT_DOWN:	y=winHeight-y;	startMotion( x,y);	break;    case GLUT_UP:	stopMotion( x,y);	break;    } }void myReshape(int w, int h){    glViewport(0, 0, w, h);    winWidth = w;    winHeight = h;}void spinCube(){    if (redrawContinue) glutPostRedisplay();}voidmain(int argc, char **argv){    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);    glutInitWindowSize(500, 500);    glutCreateWindow("colorcube");    glutReshapeFunc(myReshape);    glutDisplayFunc(display);    glutIdleFunc(spinCube);    glutMouseFunc(mouseButton);    glutMotionFunc(mouseMotion);	glEnable(GL_DEPTH_TEST);     glMatrixMode(GL_PROJECTION);    glLoadIdentity();	glOrtho(-2.0, 2.0, -2.0, 2.0, -2.0, 2.0);    glMatrixMode(GL_MODELVIEW);    glutMainLoop();}