49 lines
1.8 KiB
Markdown
49 lines
1.8 KiB
Markdown
# Piecasso — A desktop Paint application in PyQt
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Express yourself with PieCasso, the only painting programme to feature
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ready made pictures of pie.
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Piecasso is a clone of the Paint programme from Windows 95 (ish) with a
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few additions (and subtractions). The programme features standard
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tools including pen, brush, fill, spray can, eraser, text and a number of
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shapes.
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You can copy from the image, with a custom shape,
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although pasting + floating is not supported. The canvas is a fixed size
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and loaded images are adjusted to fit. A stamp tool is also included
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which is pre-loaded with pictures of delicious pie.
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> If you think this example app is neat and want to learn more about
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PyQt in general, [take a look at my ebook & online course
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"Create Simple GUI Applications"](https://martinfitzpatrick.name/create-simple-gui-applications)
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which covers everything you need to know to start building your own applications with PyQt.
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## Code notes
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### Event handling
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All tools are implemented with nested event handlers, which forward
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on events as appropriate. This allows for a lot of code re-used between
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tools which have common behaviours (e.g. shape drawing). Adding the select
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region animation requires a timer (to update the crawling ants) which
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added some complexity.
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### Flood fill
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This was the trickiest part of this app from a performance point of view.
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Checking pixels directly is far too slow (full-canvas fill
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time of approx 10 seconds). Most code to achieve this in Python sensibly
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uses numpy, but I didn't want to introduce a dependency for this alone.
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By exporting the image as a bytestring, then down-sampling to a boolean
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byte-per-pixel (for match/no-match) to simplify the comparison loop, I
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could get it up to a reasonable speed.
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The search-to-fill algorithm is still pretty dumb though.
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