gerber: convert font glyphs directly

[davidperrenoud]

From irasc...@gmail.com on July 14, 2011 05:26:41

Instead of rasterizing fonts, figure out how to convert the font glyphs directly, or somehow attach to Qt's font engine...

Original issue: http://code.google.com/p/fritzing/issues/detail?id=1568

[davidperrenoud]

From irasc...@gmail.com on July 14, 2011 22:49:57

in general, the more svg elements we can convert directly, rather than going through raster conversion, the better

[davidperrenoud]

From irasc...@gmail.com on July 14, 2011 22:50:53

or sticking with rasterizing, would it be possible to do just the fonts at a higher res?

[davidperrenoud]

From irasc...@gmail.com on July 16, 2011 14:37:52

an technique called distance-mapping might work as a fast way to convert a given svg vector to a raster: http://labs.qt.nokia.com/2011/07/15/text-rendering-in-the-qml-scene-graph/

[davidperrenoud]

From irasc...@gmail.com on July 19, 2011 15:51:35

QPainterPath has an addText function which takes a QFont. The resulting path is composed of moveTo, lineTo, curveTo. One would have to approximate the curves (both cubic and quadratic bezier) with circular arcs.

There is a paper about the cubic bezier approximation at http://itc.ktu.lt/itc354/Riskus354.pdf , also see http://www.cosy.sbg.ac.at/~helmut/Teaching/SEDissertanten/program.pdf , and http://cgcad.thss.tsinghua.edu.cn/~yongjh/papers/cad2000v32n4p253.pdf

[davidperrenoud]

From irasc...@gmail.com on July 20, 2011 03:22:49

QPainterPath also has a number of path-to-polygon conversion functions, so depending on how closely these curves are converted, it might be possible to use these directly. This could also be the means for converting elliptical arcs--because QPainterPath's arcTo is elliptical.

[KjellMorgenstern]

A while ago I made some progress on this.
I have experimented with single line fonts from https://k40lasercutter.com , and was able to render them into svg paths from the Qt font engine.
In a separate experiment, we can turn svg paths into gerber quite reliably, by interpolating Béziers with arcs, usually a few (less than ten) arcs are enough for one Bezier. This is recursive, meaning we just split the Bézier into arcs until we have reached an approximation with a desired maximum error.
In the long term this will benefit gerber formats, and enable CNCed or additive (3d printed) texts.
We have also prepared a custom single line font that can be added to Fritzing under SIL OFL. The ones from k40 are usually commercial, and I was not able to reach anyone there to ask for a cooperation, probably got lost in their inbox.
Still, this is kind of a fun project. Because there are too many mundane (and important) problems in Fritzing, it will take more time and releases until solving this issue.