hello everyone,

I am trying to rotate a mesh towards the center of the screen so that it 'looks' at the center.  This needs 3 angles to rotate the mesh in a x, y and z direction. The problem is, i dont know how to retrieve those values. At this moment i am in a fight with vectors, and trying to understand the dot and cross product, but with no succes...

to run the sketch, you need the peasycam library and the hemesh library

1. import peasy.*;
   
   import wblut.math.*;
   import wblut.hemesh.modifiers.*;
   import wblut.hemesh.kdtree.*;
   import wblut.hemesh.creators.*;
   import wblut.hemesh.tools.*;
   import wblut.hemesh.*;
   import wblut.hemesh.subdividors.*;
   import wblut.geom.*;
   
   import processing.opengl.*;
   import javax.media.opengl.*;
   // cam
   PeasyCam cam;
   PVector center, angle, child;
   HE_Mesh m; 
   PVector direction = new PVector();
   void setup() {
     size(800,600, OPENGL);
     background(255);
   
     // camera
     cam = new PeasyCam(this, 100);
     cam.setMinimumDistance(1);
     cam.setMaximumDistance(500);
     center = new PVector(0,0,0);
     angle = new PVector(1,0.1,0.3);
     angle.normalize();
     child = new PVector();
   
     child.set(angle);
     child.mult(100);
   
     //angle from child to center
     PVector angleToCenter = new PVector();
     angleToCenter.set(angle);
     angleToCenter.mult(-1);
   
     float d = 10;
     float h = 50;
     float w = 70;
   
     HEC_Creator c = new HEC_Box(this).setDepth(d).setHeight(h).setWidth(w).setWidthSegments(10).setHeightSegments(10).setDepthSegments(10);
     m = new HE_Mesh(c);
   
     double[] limits = m.limits();
     PVector minBoundingBox = new PVector( (float) limits[0], (float) limits[1], (float) limits[2]);
     PVector maxBoundingBox = new PVector( (float) limits[3], (float) limits[4], (float) limits[5]);
   
     float volumeX = calculateDifferences( minBoundingBox.x, maxBoundingBox.x);
     float volumeY = calculateDifferences( minBoundingBox.y, maxBoundingBox.y);
     float volumeZ = calculateDifferences( minBoundingBox.z, maxBoundingBox.z);
   
     int direction_id = 0;
     float[] volumes = {
       volumeX, volumeY, volumeZ
     };
     for(int i = 0; i < volumes.length; i++) {
       if(min(volumes) == volumes[i]) { 
         direction_id = i;
         break;
       }
     }
   
   
     switch(direction_id) {
     case 0:
       direction.set(1,0,0);
       break;
     case 1:
       direction.set(0,1,0);
       break;
     case 2:
       direction.set(0,0,1);
       break;
     }
     direction.mult(30);
     angle.mult(20);
   
     WB_Point rotationCenter = new WB_Point(0,0,0);
     WB_Vector axisDirection = new WB_Vector(1,0,0);
     float rotationAngle = 0;
    
     // horizontal axis = depth rotation
     // m.rotateAboutAxis(rotationAngle, rotationCenter, axisDirection);
   
     axisDirection.set(0,1,0);
     rotationAngle = 0;
     // vertical axis = horizontal rotation
     // m.rotateAboutAxis(rotationAngle, rotationCenter, axisDirection);
   
     axisDirection.set(0,0,1);
     rotationAngle = 0;
     // depth axis = vertial rotation
     // m.rotateAboutAxis(rotationAngle, rotationCenter, axisDirection);
   }
   
   
   void draw() {
     background(255);
     stroke(0);
     strokeWeight(1);
     lights();
     pushMatrix();
     translate(center.x, center.y, center.z);
     box(10);
     strokeWeight(3);
     stroke(255,0,0); 
     beginShape();
     vertex(0,0,0);
     vertex(angle.x, angle.y, angle.z);
     endShape();
     popMatrix();
   
     strokeWeight(1);
     pushMatrix();
     translate(child.x, child.y, child.z);
     stroke(0);
     m.drawFaces();
    
     strokeWeight(3);
     stroke(255,0,0); 
     beginShape();
     vertex(0,0,0);
     vertex(direction.x, direction.y, direction.z);
     endShape();
    
     popMatrix();
   }