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37 lines
2.0 KiB
37 lines
2.0 KiB
Painting with brushes
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:.,I don't know anything, nada, zilch, noppes about writing paint applications. So
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when I started working on Chalk, I felt I needed examples. I used the following
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sources:
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* The old Chalk brush code (http://webcvs.kde.org/cgi-bin/cvsweb.cgi/koffice/chalk/tools/kis_tool_brush.cc?rev=1.58&content-type=text/x-cvsweb-markup)
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* Peter Jodda's Perico (http://software.jodda.de/perico.html)
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* The source of the Gimp (both current and 0.99.11 -- the oldest version I could find) (http://www.gimp.org)
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* David Hodson's article on Gimp brushes (http://members.ozemail.com.au/~hodsond/gimpbrush.html)
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* Raph Levien's article on Gimp brushes (http://www.levien.com/gimp/brush-arch.html)
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Chalk uses the gimp's brush file formats: .gbr and .gih, for singe
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and pipeline brushes, respectively. These brushes contain one or more
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grayscale or rgba images. If the image is grayscale, the gray image is
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intended to be used as an alpha mask: each gray level corresponds to
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a certain alpha level, and when painting the current painting colour
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is composited in the image with this level as its alpha component. The
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image brushes should be masked -- i.e., these are coloured images placed
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on a white background. The white background should be made transparent,
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and then the brush image can be composited onto our image.
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This is currently only half supported: I make masks of everything,
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partly because I like that better, partly because until very recently
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there was no way of making out the difference between gray and rgb
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brushes because KisBrush didn't remember that bit of data.
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Making the initial mask of a brush is however by now pretty well done; the next
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problem is painting with those masks.
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Here we have two situations, one easy, one difficult. The easy one is the single
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mouse click. If the user clicks or taps with his stylus, we can composite the
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mask or the image at the pixel position of the mouse click.
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The difficult situation is drawing a line. This line needs to be antialiased.
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