anchor.diff:    
     void drawFillCircle(ctx, num x_, num y_, num radius, color) {
       ctx.beginPath();
  -    ctx.setLineWidth(2);
  -    ctx.setFillColor(color);
  +    ctx.lineWidth = 2;
  +    ctx.strokeStyle = color;
  +    ctx.fillStyle = color;
       ctx.arc(x_, y_, radius, 0, TAU, false);
       ctx.fill();
     }
  
positive.code:   }
    
    void draw() {
      num baseHeading = TAU * (heading / 360);
      num deltaX = Math.cos(baseHeading);
      num deltaY = Math.sin(baseHeading);
      num newX = x + delta * deltaX;
  
negative.code:     cleanCtx(turtleCtx);
      if (delta != 0 && penupdown == PENDOWN) {
        userCtx.beginPath();
        userCtx.lineWidth = 2;
        userCtx.fillStyle = BLACK;
        userCtx.strokeStyle  = BLACK;
        userCtx.moveTo(x, y);
        userCtx.lineTo(newX, newY);
        userCtx.stroke();
  