Question

I`m currently working out the design for simple graphic editor, who support trivial operations for two-dimensional and three-d shapes.
The point is, I want to render prototype of these shapes, as MsPaint does. And at the moment it is rendering I need to store somewhere pixels from the canvas which get covered by prototype, just in case when prototype changes to restore their state on the canvas. So, I want all my shapes to support this kind of buffering (Graphic Operation is the base class for all rendering operations):

public abstract class Shape: GraphicOperation {
        protected List<SomePoint> backup;
        public Shape(Color c): base(c) { }

        public Color FigureColor {
            get { return color; }
            protected set { color = value; }
        }
        public abstract void renderPrototype(Bitmap canvasToDrawOn);
}

The main idea is that in terms of OO design it would be great to provide the support of the buffer on base class (Shape) level, I mean for TwoDShape and ThreeDShape classes this list must be initialized in different way – for TwoDShape with TwoDPoint instances, and for ThreeDShape with ThreeDPoint instances.
But to do this, SomePoint must be base class for both two-dimensional point and three-dimensional point classes. Is it acceptable in terms of OO to derive both these classes from single base class?
May be there are too many words, but I just wanted the problem to be clear for everyone.
Edit: btw, is this the good idea to derive point classes from their king of shapes? I personally see no other options, but may be it would be better if I derive it directly from shape? Now it is:

public abstract class TwoDShape : Shape {
        protected List<SomePoint> backup;
        public TwoDShape(Color c) : base(c) { }
    }
public class TwoDPoint: TwoDShape {
        //...
}

and the same is for ThreeDPoint.

Answer 1

I don’t see any reason not to. But if the only difference between Shapes is in the type of Points they contain, why not make the Shape class itself a template, or a “generic” in Java parlance?