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Robert Pearce wrote: > Minor thing this... > In the DrawingArea section of the tutorial, on the page about arcs, > at > http://developer.gnome.org/gtkmm-tutorial/2.22/sec-cairo-drawing-arcs.html.en > the second paragraph shows how to draw an ellipse then says "this > contradicts the Cairo documentation". I don't think it does. > The apparent problem arises from a co-ordinate reference > discrepancy. When the Cairo documentation discusses ellipses, it uses > x,y,w,h to represent the bounding box of the desired ellipse. Thus > the ellipse is centred at x+w/2,y+h/2 and the translate operation > uses that as the new origin. In the Gtkmm tutorial, however, x,y > refers to the centre of the desired ellipse already, and the bounding > box would be x-width/2,y-height/2,width,height. > If you take this context difference into account, both examples do > the same thing. I would suggest, therefore, that the "This > contradicts" wording be changed to something like "This looks > different to the official Cairo documentation because we are defining > our desired position differently. They do the same thing in > reality." Terribly late reply! I found this note from April 2011 when I was looking for something else. I corrected this text in the gtkmm tutorial in September. http://developer.gnome.org/gtkmm-tutorial/3.2/sec-cairo-drawing-arcs.html.en My correction is not exactly as you suggested, but I'm convinced that it's correct. When I was working with the tutorial, I did not remember having seen your note. Obviously I did not pay due attention to it when you posted it. Kjell |