84 lines
2.9 KiB
Plaintext
84 lines
2.9 KiB
Plaintext
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IfsCompose
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IfsCompose is a plug-in for PIKA that allows
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the creation of Iterated Function System fractals by direct
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manipulation onscreen of the component transforms.
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IFS Fractals
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------------
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You may be familiar with IFS's from the screen
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hack 'Flame'. They are also the basis of fractal image compression.
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For a brief introduction to IFS's see Foley and van Dam, et
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al,. _Computer Graphics, Principles and Practice_, 2nd Ed.,
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(Addison Wesley, 1990).
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The standard references in the field are Michael Barnsley's books (though
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I haven't looked at them yet):
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M. Barnsley, _Fractals Everywhere_, Academic Press Inc., 1988.
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M. Barnsley and L. Hurd, _Fractal Image Compression_, Jones and
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Bartlett.
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Briefly, you take a point and repeatedly apply one of a set of
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transformations to it, choosing randomly between them, and plot the
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point at each step. An interesting result (the Collage Theorem) says
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that if you can find a set of transformations that break up an image
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into smaller copies of itself, then the resulting fractal exactly
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reproduces the original image. For example, here is a classic image
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of a leaf and the same image with the four component transforms
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colored distinctively.
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But the best way to appreciate this may to install this program and
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try it out. I've extended the basic concept as found in
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Foley and van Dam to include transformations in color space as
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well as in real space.
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Installation
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------------
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The included Makefile should work with minor modifications on most
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systems if you have installed Pika normally. Put the resulting binary
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in ~/.pika/plug-ins or the system-wide plug-ins directory.
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The included files gtkaspectframe.c/.h implement a modified frame
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widget that guarantees that the aspect ratio of the child widget
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remains constant when the parent is resized. It's sort of specialized,
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but if you think it would be useful for other purposes, let me know
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and I'll lobby for its inclusion in the standard gtk.
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Use
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---
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The interface is somewhat complex and it may take you a little while
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to get the hang of it. (There are 19 parameters for each
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transformation in your fractal, after all). The best way to learn is
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probably to start by making small changes, and seeing what they
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do. Click on the transformations (represented by polygons) in the
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design window to manipulate them interactively.
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Button-1: rotate/scale
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Button-2: distort
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Button-3: move
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If you hold down shift while clicking, you can select multiple polygons
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to apply the transformation to.
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Try not to click too near the center of a polygon, as this will
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amplify your actions.
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Note that if you render onto an image with an alpha channel, the
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background will be transparent (very useful for compositing several
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fractals), otherwise the background will be the current background.
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There are tutorials and some example images at:
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http://www.gtk.org/~otaylor/IfsCompose/ifs_tutorial/tutorial.html
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http://tigert.pika.technology.heckin/ifs-compose/
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Have fun!
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Owen Taylor
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