Rotating a Sphere Not on its Axis

Processing Coding Questions
1

I’m trying to rotate a sphere around another sphere using PShapes, translate and rotate, but I can’t figure out how to do it since the sphere automatically draws at 0,0,0 and as such I can only get it to rotate around its axis not some other point.

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2

basically you need a

  • static translate ( like to the middle of screen )
  • make the fix sphere
  • dynamic translate ( with rotation math )
  • make the moving sphere

+++ make something that you can look at it from all sides…
so the 3D gets visible / usable

without it you could just use 2 circles moving ( in 2D )

float er = 40,ang,speed=0.02;

void setup() {
  size(200,200,P3D);
  noStroke();
  info_print();
}

void draw() {
 background(0,0,80);
 PTZ();
}

void draw_object() {             //_________________called by / from inside PTZ
 fill(200,200,0);                // yellow
 sphere(20);                     // sun
 translate(er*sin(ang),er*cos(ang));
 fill(0,0,200);                  // blue
 sphere(5);                      // earth
 ang+=speed;                      
}


//_____________________________________ PTZ tab
int mode = 0;
float Zmag = 2;
int Zaxis=-10;                                                       
float Xmag, Ymag = 0;
float newXmag, newYmag = 0; 
int newZmag = 0;
int zoomf = 3;
float newxpos, newypos = 0;       // for PAN
float xposd, yposd = 0;           // for PAN

//_________________________________________________________________ ROTATE / TILDE and MOVE / PAN
void mousePressed() {
  if      (mouseButton == LEFT) { 
    mode=1;
  }  // ORBIT
  else if (mouseButton == RIGHT) { 
    mode=2;
  }  // PAN
  // else if (mouseButton == CENTER) { mode=3; }  // zoom mouse wheel works same , presssed or not
}

//_________________________________________________________________ mouse PT end
void mouseReleased() { 
  mode = 0;
}

//_________________________________________________________________ mouseWheel ZOOM
void mouseWheel(MouseEvent event) {
  int newZmag = event.getCount();                                     // +- 1
  //if (Zmag > 10) { Zmag += newZmag * 5; } else { Zmag += newZmag; }// from 1 to 11 go in step 1 else in step 5 
  Zmag += newZmag*0.1;
  //println("Zmag: "+nf(Zmag, 1, 2));
}

void keyPressed() {
  if ( keyCode == UP   )  Ymag -= 0.1 ;
  if ( keyCode == DOWN )  Ymag += 0.1 ;
  if ( keyCode == RIGHT)  Xmag -= 0.1 ;
  if ( keyCode == LEFT )  Xmag += 0.1 ;
  if ( keyCode == 16 )    Zmag -= 0.1 ;
  if ( keyCode == 11 )    Zmag += 0.1 ;
  //println("key: "+key); println("keyCode: "+keyCode);
}
//_________________________________________________________________ Pan Tilde Zoom
void PTZ() {
  pushMatrix(); 
  translate(width/2, height/2, Zaxis);
  // get new mouse operation  
  if ( mode == 2 ) {                              // PAN ( right mouse button pressed)
    xposd = (mouseX-float(width/2));
    yposd = (mouseY-float(height/2));
  }  
  newxpos = xposd;// xposd=0;
  newypos = yposd;// yposd = 0; 
  translate(newxpos, newypos, 0);          // move object
  if ( mode == 1 ) {  // ORBIT ( left mouse button pressed)
    newXmag = mouseX/float(width) * TWO_PI;
    newYmag = mouseY/float(height) * TWO_PI;

    float diff = Xmag-newXmag;
    if (abs(diff) >  0.01)   Xmag -= diff/4.0;
    diff = Ymag-newYmag;
    if (abs(diff) >  0.01)   Ymag -= diff/4.0;
  }
  rotateX(-Ymag);   
  rotateY(-Xmag);   
  scale(Zmag);
  draw_object();                                // THE OBJECT  see main tab
  popMatrix();
}

//_______________________________________________ SETUP PRINT INFO
void info_print() {
  println("PTZ info:");
  println("key UP DOWN RIGHT LEFT -> rotate // key PAGE UP DOWN -> zoom");
  println("mouse LEFT press drag up down right left -> rotate // mouse RIGHT press -> move // mouse WHEEL turn -> zoom");
}
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3

Note that if you need rotation of de-centered objects around a central point, the PeasyCam library is ideal for this.

http://mrfeinberg.com/peasycam/

This example is based on the demo peasycam sketch, but with two spheres instead of two boxes.

import peasy.*;

PeasyCam cam;

void setup() {
  size(200, 200, P3D);
  cam = new PeasyCam(this, 100);
  cam.setMinimumDistance(50);
  cam.setMaximumDistance(500);
}

void draw() {
  background(0);
  rotateX(-.5);
  rotateY(-.5);
  fill(255, 0, 0);
  sphere(30);
  translate(0, 0, 30 + 15);
  fill(0, 0, 255);
  sphere(15);
}

TwoSphere

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