From: Josef Wolf <jw@...>
Date: 2009-09-09T01:40:17+09:00
Subject: Re: Zoomable TkCanvas?

On Tue, Sep 08, 2009 at 07:35:31AM +0900, Joel VanderWerf wrote:
> Josef Wolf wrote:
>>  - maintain original coordinates at all zoom factors. Thus even after
>>    zoom operations, events as well as querying/moving/adding items are
>>    done as if the canvas is at zoom factor 1.0. So zoom is handled
>>    completely transparent to the user of the module..
>
> Yep, tkar does that too--object coordinates are independent of zoom level. 
> TkCanvas coordinates are hidden in the abstraction.

Hmm, somehow I fail to see how this is supposed to work.

I see zoom_by does the scaling, adjusts the scrollregion and updates the
view. IMHO, to keep coordinates independent from zoom level, you would need
to intercept query/movement/creation of the items. Without that

 TkcRectangle.new(canvas, [100,100], [300, 200])
 canvas.zoom_by(2.0)
 TkcRectangle.new(canvas, [100,100], [300, 200])

would result in two rectangles with different sizes.

>>  - turn around the y-axis (origin is at left bottom)
> Tkar has an option to flip the y-axis (and also an option to use radians 
> instead of degrees for rotation commands).
>
>>  - handle scroll bars + panning
> Check.

This is done with the help of the Window class, AFAICS. So it is not as
transparent as the Tk::AbstractCanvas module.