adapted from ex.14-10 from learning processing

platonicSolid1.pde

/*
tetrahedron
*/

float theta;

void setup() {
  size(300,300,P3D);
  background(0);
  theta = 0;
}

void draw() {
  background(0);
  theta += 0.01;
  translate(width/2,height/2);
  rotateX(theta);
  rotateY(theta);
  drawShape(50);
}

void drawShape(int t) {
  stroke(color(255,0,0));
  beginShape(TRIANGLES);
  //base
  vertex(-t*sin(PI/3),t,t*1/2);
  vertex(t*sin(PI/3),t,t*1/2);
  vertex(0,-t,t*1/2);
  
  vertex(-t*sin(PI/3),t,t*1/2);
  vertex(t*sin(PI/3),t,t*1/2);
  vertex(0,0,-t);
  
  vertex(t*sin(PI/3),t,t*1/2);
  vertex(0,-t,t*1/2);
  vertex(0,0,-t);
  
  vertex(0,-t,t*1/2);
  vertex(-t*sin(PI/3),t,t*1/2);
  vertex(0,0,-t);
  endShape();
}