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A Perspective on Chalk's Design
Chalk's codebase has been through as many changes as the app's name
itself. It started with KImageShop (hence the 'kis' prefix one finds
everwhere, and which would have been unnessary had Chalk used
namespaces, one fancies), then became Krayon to end up as Chalk. The
stated design goal was to create a application geared towards the
more artistic user; the kind of user who settles down with his
tablet to create a spot of Art. It ended up as a Gimp-clone, a Kimp,
so to say.
This document was the basis for a discussion on the chalk mailinglist:
http://lists.kde.org/?l=kde-kimageshop&m=106530035202770&w=2. See the
answer for some answers to the questions at the end.
Design Patterns
Patrick Julien restructured Chalk to use a lot design patterns. Chalk
appears to have a very solid base for blasting pixels to the screen,
zooming, selecting and moving. These are what I recognize as his
changes:
* Change brushes handling to a generic Mediator pattern
(kis_resource_mediator). Resources are brush shapes,
patterns (and colours, too?) Patrick intended a Flyweight
here.
* The composite pattern is used in paint devices, layers, channels,
etc. (What about masks?)
* Change colourspace handling to a Strategy pattern
(strategy/kis_strategy_color)
* Change moving chunks of painting to a Strategy pattern
(strategy/kis_strategy_move)
* kis_factory points towards a Factory pattern Creates the
pluginserver and resourceserver.
* Tools are created by a Factory pattern (but it isn't
dynamic yet): kis_tool_factory. Tools are intended to
become tdeparts.
* There's the start of a Memento pattern for tools, but it
doesn't seem to be used (kis_tool_memento). It was an
experiment that didn't pan out.
* The Builder pattern is used to do conversion to and/or
from ImageMagick. I guess this is used for importing
images in other file-formats than .chalk. An idea at one
was to use Koffice filters, but that didn't work because
images are rather different from other office documents.
* Flyweight pattern used for background tiles.
kis_background.
* Nameserver. Perhaps not a pattern -- at least not one
with an obvious GOF name. Appears to be computing a
number for new layers and new documents.
* kis_render. Interface implemented by kis_paint_device
and kis_image.
* Rename kisTool to kisToolInterface -- but the file is
still called kis_tool. (This is intentional, and should
be kept in the style guide.)
* Addition of kis_types. Defines shared pointer pointers
to core chalk objects: image, paintdevice, channel,
mask, layer etc.
* Tile architecture. There's Mediator and a Singleton
pattern here at least. This stuff seems to work, doesn't
need hacking at the moment.
* Visitor pattern used to flatten an image or merge
layers. Merging exposes a funny bug where the tiles
are re-arranged in an interesting mosaic pattern.
User interface
Chalk uses a fairly ugly side-panel to collect what are palettes
in other applications. I would prefer dockable, attachable
palettes myself. Doesn't KDE have a lib for that already?
ui/labels
These classes are used in the statusbar.
ui
The dialogs appear to be created by hand, not with Qt
Designer. Besides, many are inoperational.
other
The canvas, rules and sidebar panels are defined here, too,
nicely separated.
Tools
Working: select_rectangular, test, zoom, colorpicker, paste, move
Not working: airbrush, brush, colorchanger (no idea what it should
do), ellipse, eraser, fill, line, pen, polygon, polyline,
rectangle, select_contiguous, select_elliptical, select_freehand,
select_polygonal, stamp
Missing tools: convolve, smear, smudge, whirl, charcoal, chalk,
oils, clone, select_by_colour
Plugins
The single plugin example has been present in chalk since about day
one, as far as I can see. It doesn't show anything about what one
can do with plugins.
To judge from the code in kis_plugin_server, it never got beyond
an idea. (kdDebug() << "hallo\n"...)
(This code should be removed.)
ImageMagick
There still appear to be some dependencies upon ImageMagick (builder
subdir). What are these for, and should they stay? Is it for
importing/exporting foreign file formats?
Undo/Redo
Undo and Redo make use of the standard KDE mechanism, which I don't
really understand either.
Obsolete files
The following files appear to be unused:
core/helper/kis_timer
core/helper/kis_scopedlock (Replaced with QMutexlocker)
core/kis_krayon (was predecessor of kis_resource)
core/kis_mask
core/kis_util
ui/kis_krayon_widget
Random head-scratchings
- Why the QUANTUM redefinition: the number of bits per channel,
8 for 32-bit colour, 16 for 64-bit colour.
- is_mask unimplemented? What was it meant to do, or is it an
interface?
- nameserver presents unique numbers for new layers and images.
- what does 'upscale' do? in 8 bit/channel color mode, upscale
doesn't do anything. However, downscale and upscale in > 8 bit,
this is needed to covert the color for the actual display
rendering, i.e. X, etc, only do 8 bit color. Using this
everywhere you work on color will keep chalk color channel
bit depth independent.
- Is KisVector only used in obsolete tools?
- I take it that the two tests that are present in chalk/test
are obsolete?
- what with the dummmmmy.cc?
- which bits of the chalk/ui files are still relevant?
- kis_selection.h needs to be included to compile code that
uses kis_paint_device, and I wonder why.
- what is paint-offset?
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