"Ink trap" : ink trap.

It's to prevent the ink inside a sharp edge running in. As your image shows, the outside joints are regular (or rather, if the outside joints were blunt as well that would be by design only, not as a practical precaution).

Inside and outside, it can be a good idea to truncate very sharp angles to mitigate the exaggerated effect that results when users apply a stroke (I know, but it's not like we can stop them doing it).

Inktraps of course, but they're used in display fonts as well. This got me to suspect that there may be also other reasons.

Strokes - hmm, interesting point. But in my case I certainly wouldn't compromise the design of the contours for preventing stroke inconsistencies.

I’ve sometimes blunted outside very acute angles to avoid ugly on-screen rasterizing effects (where the displayed glyphs will display unwanted spurs, particularly at smaller sizes), although it’s seemed to me an inelegant solution to the problem.

David

It provides a more decisive letter shape.
A sharp point is unfinished, in the sense that its exact position is determined by the output device (or size), not the type designer, and this will happen differently depending on relative sharpness, whereas as a designer one wants a more consistent shape.

From me, this comes from the old practice of leaving room for the router bit.

For *extremely* sharp corners, under some rasterizers, sometimes very bad things would happen. Leastways, that's what I got taught at Adobe, and I remember seeing the effects a few times, though that was Long Ago.

Thanks for all your comments!

I love traps- they do so many things.

See also:
http://www.themicrofoundry.com/ss_trapping1.html

hhp

where to set joining type of glyphs from U-joining to D-joining in fontlab

In the “Node Properties” panel.

Make this appear by first control-clicking (Mac) on a node, then on “Properties”, near the bottom of the resulting pop-up menu.

[Sorry, not what you meant…]