Negative sized viewport
The current state of the BiDi branch (fb7e2980), in combination with a large padding results in an assertion failure on startup in some VTE-based frontends (e.g. Tilix, ROXTerm), complaining about the RingView having a negative amount of lines.
What probably happens: There's an allocation provided by GTK, which has at least 0x0 size (or is at least 1x1 guaranteed?), not yet adjusted to the actual window size of the app, then we "subtract" the paddings, and the result is a viewport of e.g. -200x-200 pixels.
This is presumably intermittent in these apps. E.g. in Tilix the number of the requested rows is negative twice the padding, meaning that the font size is uninitialized (1x1) at this point.
I'll work it around in the BiDi branch, but I'm wondering if we could (and should) refactor our code to provide a generic protection, e.g. to compute the padding dynamically, making sure that the actual terminal canvas is at least 0x0...?