mirror of https://github.com/python/cpython
70 lines
4.6 KiB
HTML
70 lines
4.6 KiB
HTML
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<HTML><HEAD><TITLE>Using WASTE</TITLE></HEAD>
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<BODY>
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<H1>Using WASTE</H1>
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<HR>
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WASTE is an almost-compatible TextEdit replacement which overcomes
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some of the limitations of it (like the 32K limit) and provides some extensions
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(drag and drop, images, undo support). Moreover, it has a much cleaner interface
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and is therefore easier integrated in Python. <p>
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WASTE is written by Marco Piovanelli, <A HREF="mailto:piovanel@kagi.com"><piovanel@kagi.com></A>,
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and copyrighted by him. You can always obtain the latest version (for use in C
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or Pascal programs) and the documentation from
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<A HREF="ftp://ftp.dsi.unimi.it/DSI/piovanel/WASTE"><ftp://ftp.dsi.unimi.it/DSI/piovanel/WASTE></A>.
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We explain the useage of waste here by showing how to modify the TextEdit based
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<A HREF="textedit/ped.py">ped.py</A> of the
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<A HREF="textedit.html">previous example</A> into the waste-based <A HREF="waste/wed.py">wed.py</A>,
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so you should have both sources handy. <p>
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Functionally, <code>wed.py</code> provides three new things: resizable windows, a horizontal
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scroll bar and undo. <p>
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Let us look at the code, first at the application class <code>Wed</code>. The only real change is that
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we now handle <code>undo</code>. Aside from enabling it in the creation routine and the addition of
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a callback routine there is a bit of new code in <code>updatemenubar</code>: Waste not only handles
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the full details of implementing undo, it will also tell us what the next undo operation will undo
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(or redo). We use this to our advantage by changing the undo menu label to tell the user. <p>
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The <code>WasteWindow</code> has seen a bit more change. Initialization of the waste data structure is
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a bit different, in that we can specify some options at creation time. Also, waste has no <code>SetText</code>
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method but a <code>UseText</code> which expects a handle as parameter. We have to be <EM>very</EM> careful
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that we keep this handle around, because Python will happily free the handle if we have no more references
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to it (and I doubt that Waste would like this:-). A final difference in <code>open</code>
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is that we use a large number for the destination rectangle width, because we will use a horizontal scroll
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bar. <p>
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The <code>idle</code> method is a bit more involved, since we also call <code>WEAdjustCursor</code> to
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provide the correct cursor based on mouse-position. Users like this. <p>
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<code>Getscrollbarvalues</code> is simpler than its' TextEdit counterpart because Waste correctly
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updates the destination rectangle when the document changes. Also note that waste uses accessor functions
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to get at internal values, as opposed to direct struct access for TextEdit. <p>
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<code>Scrollbar_callback</code> on the other hand is more elaborate (but also provides more functionality).
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It also handles horizontal scrolls (scrolling one-tenth and half a screenful with the buttons). This
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function is also "multi-font-ready" in that scrolling one line will do the expected thing in case of multiple
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fonts. We will implement a multi-font editor later. A minor annoyance of Waste is that is does not provide
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a pinned scroll, so at the end of our callback routine we have to check that we have not scrolled past the
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beginning or end of the document, and adjust when needed. <p>
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<code>do_update</code> is also changed, because Waste is completely region-based (as opposed to rect-based).
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Hence, we erase regions here and we can also return immedeately if there is nothing to update. <p>
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<code>Do_postresize</code> is new: because Waste uses accessor functions we can now modify the viewRect from
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Python, which is impossible in the Python TextEdit interface, and hence we can implement resize. The
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<code>do_key</code> and <code>do_contentclick</code> methods have also seen minor changes, because the
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corresponding waste routines need a bit more information than their TextEdit counterparts. The Cut/copy/paste
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code is simplified, because Waste uses the normal desktop scrap. <p>
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Implementing undo is a wonder of simplicity: Waste handles all the details for us. Also, the new
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<code>can_paste</code> method (which controls greying out of the paste menu entry) is an improvement
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over what <code>ped</code> did: in ped it was possible that paste was enabled but that the data on the
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scrap was incompatible with TextEdit. No more such problems here. <p>
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<hr>
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That is all for now. At some point in the future I will extend this editor to incorporate multiple fonts and
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pointsizes, pictures and possibly drag-and-drop editing but I will first have to write the code for it.
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For now you will have to go back to the <A HREF="index.html">index</A> to pick another example.
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