#include <stdio.h>
#include <stdlib.h>
#include <GLUT/glut.h>

/*
 * interp.c: cubic interpolating polynomial curve
 *
 * Of necessity, this is 2D.
 *
 * All calcs are 3d, though.
 *
 * 3/31/03 pjf
 *
 */

GLfloat p[4][3] = { { -0.5, 0.0, 0.0 },  {-0.15, -0.5, 0.0 },
                    { 0.15, 0.5, 0.0 }, { 0.5, 0.0, 0.0 }};

int ww,hh;


float b0(float u) { return -4.5 * (u-0.333) * (u - 0.666) * (u-1.0); }
float b1(float u) { return 13.5 * u * (u-0.666) * (u-1.0); }
float b2(float u) { return -13.5 * u * (u-0.333) * (u-1.0); }
float b3(float u) { return 4.5 * u * (u-0.333) * (u-0.666); }

/* display callback */
void display() {
 float u;
  int i;
 glClear(GL_COLOR_BUFFER_BIT);
 glColor3f(1.0,1.0,1.0);
 glBegin(GL_LINE_STRIP);
  for (u=0.0;u<=1.0;u+=0.001) {
   GLfloat x = b0(u)*p[0][0] + b1(u)*p[1][0]  + b2(u)*p[2][0] + b3(u)*p[3][0];
   GLfloat y = b0(u)*p[0][1] + b1(u)*p[1][1]  + b2(u)*p[2][1] + b3(u)*p[3][1];
   GLfloat z = b0(u)*p[0][2] + b1(u)*p[1][2]  + b2(u)*p[2][2] + b3(u)*p[3][2];
   glVertex3f(x,y,z);
   }
  glEnd();
  // now draw boxes around control points
 glColor3f(1.0,0.3,0.3);
  for (i=0;i<4;i++) {
   GLfloat x = p[i][0] - 0.02;
   GLfloat y = p[i][1] - 0.02;
   GLfloat z = p[i][2];
   glBegin(GL_LINE_LOOP);
    glVertex3f(x,y,z);
    glVertex3f(x+0.04,y,z);
    glVertex3f(x+0.04,y+0.04,z);
    glVertex3f(x,y+0.04,z);
   glEnd();
   }
 glFlush();
 }

int curcp = -1;

/* mouse: called when a mouse button is pressed or released.
   btn identifies which button; state identifies "press" or "release" */
void mouse(int btn, int state, int x, int y) {
 //fprintf(stderr,"mouse: btn %d, state %d, location (%d,%d).\n",btn,state,x,y);
 if (state==GLUT_UP) { // up
  curcp = -1;
 } else {
  int i;
  float xmouse=2.0*x/ww - 1.0; 
  float ymouse=2.0*(hh-y)/hh - 1.0;
  float zmouse=0.0;
  //fprintf(stderr,"Mousedown @ %f %f\n",xmouse,ymouse);
  float d;
  for(i=0;i<4;i++) {
   float d=(xmouse-p[i][0])*(xmouse-p[i][0]) + 
           (ymouse-p[i][1])*(ymouse-p[i][1]) +
           (zmouse-p[i][2])*(zmouse-p[i][2]);
   if (d<0.007) break;
   };
  if (i<4) { // valid hit
   curcp = i;
   };
 }
 }

/* called initially (before first call to display()) and whenever the
   window is resized */
void reshape(int w, int h) {
  fprintf(stderr,"reshape: new size %d x %d.\n",w,h);
  // must update viewport and clipping planes
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glMatrixMode(GL_MODELVIEW);
  ww=w; hh=h;
}

void motion(int x, int y) {
 float xmouse=2.0*x/ww - 1.0; 
 float ymouse=2.0*(hh-y)/hh - 1.0;
 float zmouse = 0.0;
 //fprintf(stderr,"Motion: loc (%d %d).\n",x,y);
 //fprintf(stderr,"Motion @ %f %f\n",xmouse,ymouse);
 if (curcp == -1) return;
 p[curcp][0] = xmouse;
 p[curcp][1] = ymouse;
 p[curcp][2] = zmouse;
 glutPostRedisplay();
 }
 
void init(void) {
 /* nothing to do! */
 }

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutCreateWindow(argv[0]);
    glutReshapeFunc(reshape);
    glutDisplayFunc(display);
    glutMouseFunc(mouse);
    glutMotionFunc(motion);
    init();
    glutMainLoop();
    return 0;
}