float side = 100;
float rad60=60*PI/180;

float rotx = PI/4;
float roty = PI/4;

void setup() {
  size(800,600,P3D);
}
void draw() {
  background(0);
  translate(width/2.0, height/2.0, -100);
  rotateX(rotx);
  rotateY(roty);
  
  drawtetrahedron();
   
}
void drawtetrahedron() {
   beginShape(TRIANGLES);
   vertex(-side/2,0,0);
   vertex(0,sin(rad60)*(-side),0);
   vertex(side/2,0,0);    
  endShape();
  beginShape(TRIANGLES);
   vertex(-side/2,0,0);
   vertex(0,sin(rad60)*(-side)*.5,sin(rad60)*(side));
   vertex(side/2,0,0);    
  endShape();
   beginShape(TRIANGLES);
   vertex(-side/2,0,0);
   vertex(0,sin(rad60)*(-side)*.5,sin(rad60)*(side));
   vertex(0,sin(rad60)*(-side),0);    
  endShape();
    beginShape(TRIANGLES);
     vertex(0,sin(rad60)*(-side),0);
     vertex(0,sin(rad60)*(-side)*.5,sin(rad60)*(side));
       vertex(side/2,0,0);
  endShape();
  
}
void mouseDragged() {
  float rate = 0.01;
  rotx += (pmouseY-mouseY) * rate;
  roty += (mouseX-pmouseX) * rate;
  //println("rot x is "+rotx*180/PI+"degrees and roty is "+roty*180/PI);
}