Peter, thanks for the pointers, again. I have now used itemdelete. And I have looked at ltk.lisp as well as the on-line ltk docs too. The latter suggested that removing things could be accomplished by using delete in place of create.
So I looked at create-line's source, and set up delete-line using it as a model. Using itemdelete and your comments, I found it worked on a canvas item object such as results from create-line.
I was, however struck by the way any of these operated. I built 2 buttons in a canvas, one labeled Draw, the other Erase, and attached commands to them.
Draw does the obvious: (create-line canvas (list 100 100 200 200)). Erase in the form (delete-line canvas (list 100 100 200 200)) does nothing. However, if I crib from your more example in which you create a canvas and bind (create-line canvas (list 100 100 200 200)) to a symbol - c in your example- then (delete-line canvas c) attached to the Erase button works.
I (tentatively) conclude that itemdelete and its relatives delete only things they can "know" about. Probably (clearly!) I do not know how to rescue the handle returned by (create-line ..) other than by binding it to a symbol, which may be the difficulty. But I (tentatively) conclude that things like ltk distinguishes between a "known" line and a set of pixels which form a line in a canvas, but to which a symbol has not been explicitly attached.
Is this a fair comment, may I ask ? Peter Herth wrote:
Hi Greg,
what you are looking for is itemdelete. You can pass it either an integer canvas handle or a canvas item object. There is also the clear method which removes all items from a canvas. Though usually I try to reuse canvas items by re- configure -ing.
HTH, Peter
On Tue, Jan 5, 2010 at 5:58 PM, Greg Bennett gwbennett@sentex.ca wrote:
Good morning and Happy New Year, all.
I have trolled through ltk.lisp in an attempt to discover how to erase things .. lines, rectangles, ovals .. drawn by create-line etc..
I was looking for things like erase-line or delete-rectangle, but could not find anything like this. The closest I came to discovering this sort of functionality was the destroy facility, which seems to destroy widgets. In drawing a shape, however, I may do not usually create it explicitly as a widget with an associated symbol to feed to destroy; must I do this under ltk ?
More than likely I have simply missed something (sigh).
Thanks in advance for any help and advice.
Cheers /Greg Bennett
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