I think I did not yet officially announce LPE... from our wiki: __________________
Live path effects (LPE)
Live path effects (not to be confused with extension effects or SVG filters) are a new way to non-destructively modify path and shape objects. Path effects affect the path data of an object but not its style. The original path is preserved and can be edited directly on-canvas, and the path effect applied to it will be updated live.
In this version, we include several path effects that are analogous to the corresponding extension effects (such as Path along Path effect and Pattern along Path that replaces the extension of the same name). The most important advantage of path effects is that they are, indeed, live - you can still edit the original path and the effect will update in real time (unlike the extension effects which were one-time one-way transformations). In the future, we plan to reimplement most if not all of path-changing extensions as live path effects.
Live path effects were developed by Johan Engelen as part of the GSoC 2007.
= Applying effects =
Path effects are applied through the Path Effects dialog (opened from the Path menu, or by pressing Ctrl+Shift+7. This dialog is also used for controlling the effect's parameters and for removing effects.
When a path with a path effect applied is selected, the statusbar description mentions that, for example "Path (4 nodes, path effect)".
There is a special Paste Path Effect command (Ctrl+7) that can be used to copy effects from one path to another. [edit] Editing effect parameters
When switching to the node edit tool (F2), the original path can be edited. The original path is shown as a red helper path. Normal path operations, like simplify, still work.
Some parameters of effects can be edited on-canvas. For example, path parameters can be node-edited, by pressing the "edit on-canvas" button in the Path Effects dialog. Press "7" to cycle through the different on-canvas editable parameters. This way, one can edit the parameters without opening the Path Effects dialog. The statusbar tells the name of the parameters that is currently being shown.
= Available effects =
Path along path
The Path along Path effect can curve a path along another path. When this effect is applied to a path, it can be bend along another path (called bend path). With the node edit tool, both the original path and the bend path can be changed on-canvas and the result is updated live. This provides a direct equivalent of "vector brushes" or "skeletal strokes" features in other vector editors.
In the effect's control panel in the Path Effects dialog, you can select how many copies of the original path are put along the bend path (either single or repeated) and whether it is stretched to fill the bend path. In this dialog you'll also find a button to edit the bend path on-canvas and a button to paste a new bend path from clipboard. A possible workflow is this: you select and copy the new bend path to the clipboard, then select the path you want to bend, apply the Path along path effect, and paste the bend path with the paste button next to 'bend path'.
Pattern along path
The Pattern along Path effect can curve a path along another path. When this effect is applied to path A (called skeleton), another path B (called pattern) can then be passed as a parameter. The result is that path B is bent along path A. With the node edit tool, path A can be changed on-canvas and the result is updated live. This provides a direct equivalent of "vector brushes" or "skeletal strokes" features in other vector editors.
In the effect's control panel in the Path Effects dialog, you can select how many copies of the pattern are attached (either single or repeated) and whether the pattern is stretched to fill the skeleton path. You can also choose the pattern for the selected skeleton [either directly or] by pasting it from clipboard (that is, you select and copy to the clipboard the pattern, then select the skeleton, apply the Path along path effect, and paste the pattern). The Scale width parameter allows you to change the width of the pattern applied to the path.
Stitch Subcurves
The Stitch Subcurves effect connects points from two subpaths of the path with straight line or curved segments, i.e. the stitches. It looks a lot like the Effect Lines from Expression 3. The result is also referred to as "String Art". For some examples of string art, see http://members.shaw.ca/jillbritton/string_art/jbstringart.htm.
The shape of the connecting paths can controlled by the stroke path parameter. This could be used to draw 'hair-shaped' connecting paths with sharp end-tips. Other controls include the number of paths, the variation in spacing between the connecting paths (clustering) and also whether the start and end points of the stitches should like exactly on the original subcurves or can stray randomly around them. Finally the width of the stroke path can be varied.
Note that this effect can only be applied to a path with two subpaths in it, hence 'subcurve' in the name. Use Path > Combine to create such a path from two separate paths.
Example file: live-path-effects-curvestitch.svg
Example file showing cooperation between Stitch Subcurves and Path along Path: live-path-effects-curvestitch-hair.svg
Gears
The Gears effect is a toy effect. It generates a chain of interconnected gears from the path that has the effect applied to it. The nodes of the path define the centers of the gears. The first 3 nodes are special; the first defines the start angle of the chain, the second defines the center of the first gear and the third knot specifies the radius of the first gear. That is, to create a chain of 2 gears, you will need a path with 4 nodes; for 3 gears, 5 nodes, and so on.
Example file: live-path-effects-gears.svg
= Development of new effects =
One of the goals of the Summer of Code project was to make it easy to create new effects. There is a framework that greatly simplifies effect implementation; very little code is needed to get the effect hooked into Inkscape. This leaves valuable time for the actual effect to be implemented. See the http://wiki.inkscape.org/wiki/index.php/MakingLivePathEffects wiki page for an explanation of how to get started with your own effect!
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I'd really like people to test things and to get feedback. It already works very nicely from my point of view, but that is also because I know how to use it! I hope it is intuitive enough to be used, if not: please let us know!
Kind regards, Johan Engelen