Hi, First, let me thanks you for all your clear comments.
> > This is, in my mind, both a usage and a design flaw. > > You are creating (and throwing away) instances of drawable > objects to the draw method of a paper instance. But what does > paper.draw() actually do with the drawable object? Call a draw method > within it? No, actually the paper instance is a subclass of a canvas from an external module. And this one have a stroke() method. In reading your comments, I think it's now clear that I must get back and let any primitive have an inner draw() method ( a subclass of Drawable object in our case). > If so, that is when you should pass the paper instance (or > just the part needed -- clipping rectangle perhaps?). In fact, my approach was a bad one : in initialising the paper instance, I was already clipping it. If I wrote : p = Paper(-5,-5,5,5), all drawings made on that paper will be clipped inside a rectangle with lower-left corner (-5,-5) and upper-right corner (5,5). Now, I think it's better to clip after all primitives have been added to the paper. > > The actual implementation of draw() for each primitive will have > to handle clipping to the boundaries of the Canvas object that is passed > to it. > > You'll notice that the only place the primitive needs to know > about the canvas is in its specific draw method. And only at that time > is the canvas (paper) passed to it. > > Instead of the concept; > > Paper, draw a line from x to y > > (and having to pass the "paper" to the initializer of the line > primitive), you have to think in terms of: > > Line, draw yourself on this paper > > Or, if you consider the last example above… Compare that to your > example: > > -=-=-=-=- > paper.draw( Line( paper, x1, y1, x2, y2) ) > -=-=-=-=-=- > > Here, you are telling the paper to do the drawing, and passing > it a Line instance (and passing it the paper it is supposed to be drawn > on). Why? The paper isn't drawing the line on itself… While > > -=-=-=-=- > Line(Point(x1, y1), Point(x2, y2)).draw(paper) > -=-=-=-=- > > initializes a Line instance, then asks it to draw itself using paper as > the surface to be drawn upon. Yes I was wrong, that's all clear now. Thanks again, this was very helpfull. 6TooL9 -- http://mail.python.org/mailman/listinfo/python-list
