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📁 Tcl 语言的入门级图书
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<A NAME="top"><H1>Canvases</H1>


<P> Canvases are named after artists' canvases.  They are meant to be a blank
subwindow on which you can put almost anything.  The things you put
on a canvas are called <CITE>items.</CITE>

<P> Items can be any of the Tk widgets as well as some geometric figures: lines,
curves, rectangles, ovals, and polygons.

<P> Canvases can be set up so that users can drag some of their items around with
a mouse.

<P> There is a mechanism for generating a postscript image of a canvas but it
does not reproduce other widgets that that have been loaded into the canvas.

<P> This chapter develops a rather complicated script which permits you to
experiment with the geometric figures that canvas widgets support.  The third
section describes how to use the script.  Later in the twelfth section, you will
find three three exercises devoted solely to the implementation of this
script.

<P> <UL>
<LI> 
Introduction, Subwindows and Scrolling
<LI> 
Anchoring and Discrete Scrolling
<LI> 
A Script for Examining Canvas Items
<LI> 
The Oval is a Typical Item
<LI> 
Canvas Tags
<LI> 
A Tour of Canvas Items
<LI> 
Changing Option Values
<LI> 
Moving Items
<LI> 
Identifying an Item or Tagged Set under the Mouse
<LI> 
Canvas Object Actions
<LI> 
Postscript
<LI> 
<CITE>Implementing the Item Examining Script</CITE>
<LI> 
Solutions to Exercises
</UL>
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<STRONG>Author</STRONG>
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<P>
<I>Jun 17, 1998</I>
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