Automatic smoothing of hand-drawn lines

[pascal-niklaus]

Is your feature request related to a problem? Please describe.

Hand-drawn lines often look shaky...

Describe the solution you'd like

...applying some smoothing algorithm can clean-up such lines

Possible solution

Since I have been playing with the gromit source code, I have also implemented a smoothing option.

Basically, when a line is completed, it first applies a point reduction using the Douglas-Peucker algorithm, and then interpolates among the remaining points with centripetal Catmull-Rom splines.

The general shape and start and end points are preserved, and the smoothing degree can be set.

Here is an example with relatively strong smoothing.

Before spamming this repo with PRs, I wanted to discuss (1) whether such an option is useful, and, if yes, (2) how it is best integrated. For the moment, I just have an additional tool called SMOOTH, but there could be a "smooth=..." option for the PEN tool.

To provide a perspective on the extent of code addition, the entire smoothing logic is a bit less than 200 lines of code, in an additional file smooth.c.

[bk138]

@pascal-niklaus Neat idea! Sorry for the delay, I was busy with €€€-work. I guess a separate tool aka GromitPaintContext makes sense as the smoothing is not applicable to ERASER, RECOLOR OR LINE. Maybe call it SMOOTH_PEN ?

[bk138]

Implemented by 19a5569