Live Path Effects
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 the version 0.46 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) are included. 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).
Details about operation
The following schematic tries to explain how LPE work.
original style ------------> output style original path --> LPE --> output path ^ | parameters
The original style and path are from the path that the effect is applied on. The output is what is visible on screen. What is very important to notice is that output style equals original style.
The parameters can be paths, numbers, points, text, in principle anything.
Path effects are applied through the Path Effects dialog. This is 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 gives details, 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.
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 these 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.
Currently available live path effects are:
- Pattern along path
- Stitch subpaths
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!