[solved] Shapestring Tracking

[chrisb]

The tracking of a ShapeString is said to be the addisional distance between the characters. I thought until now that this doesn't work but I was wrong, the values I entered where far too small to have any effect. However, I don't understand the meaning of the units and I am unsure how to reliably control it:

I made a test with FreeSans.ttf and entered some text at a height of 10. If I set the tracking to 1000mm (yes, that's one meter while the height of a character is 18mm ) I get additional spacing of 8.3333 mm. And even worse, if I double the height of the string the additional space is doubled as well. So it is definitely not a distance, but rather a factor, but what is it multiplied with?

Does anyone know more about this?

OS: Ubuntu 14.04.5 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.11379 (Git)
Build type: None
Branch: master
Hash: 654276c49d1b66cf3c2a5ec538629c6d9f77c489
Python version: 2.7.6
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 7.1.0

[wandererfan]

Does anyone know more about this?

This is a bug in FT2FC.cpp. The tracking value needs to be scaled.

From a quick review, 1/64 of a pixel is the "natural unit" in FreeType (the library that understands font definitions) and a pixel's size changes with the font size and device resolution. So tracking needs to be translated into something horrible like font-size-in-points/72 points-per-inch * ??device-dots-per-inch * 64. Plus changing font height in mm into points.

If you make a ticket, I'll try to find time to relearn FreeType and fix it.

wf

[chrisb]

Done: issue #3094.
The test file should look like this, if you have the appropriate font. The ShapeStrings are two capital letters "I". I can add a file using the MacOS fonts if needed.

[wandererfan]

This should be fixed by git commit 674aabe8.

[Kunda1]

@chrisb please mark as [Solved]
Thanks WF for the fix!

[chrisb]

Thank you very much. Now I will have to revisit all my files containing ShapeStrings if they contain some monstrous tracking values .

[wandererfan]

You're welcome.

[DeepSOIC]

Hmm, should I teach FCTeleport to do it automatically?

[sgrogan]

Hmm, should I teach FCTeleport to do it automatically?

Would be interesting to see FCTeleport handle this. Would be a good use case of the POC.

[chrisb]

I wonder if it's worth the effort. As a pure guess I would say that most people who have tried it have entered a value during the creation process. And they have probably forgotten about it, because nothing visible has happened. In the example on the Ubuntu it was a deviation of 8/1000 mm, on the mac it was even less.
Since the ShapeStrings are usually not construction elements with tight fitting or other high precision requirements I would neglect it.