code: private void setFrame(int a, int b, float offset) {
  		current = (Shape) shapes.get(a);
  		next = (Shape) shapes.get(b);
  		this.offset = offset;
  		pointsDirty = true;
  	}
docs: Set the frame to be represented
  
  @param a The index of the first shape
  @param b The index of the second shape
  @param offset The offset between the two shapes to represent