Module measure 

Pango-backed TextMeasure.

The one part of the engine that needs a font stack. Everything about this implementation is shaped by the thing it must not do: xtext’s find_next_wrap (xtext.c:3685) called backend_get_text_width_emph per character, and each of those did a pango_layout_set_text + pango_layout_get_pixel_size round trip. That is the single hottest path in xtext’s append and the reason resizing a large buffer hitches.

Here:

• the unit of work is a run, because that is all the trait exposes;
• one pango::Layout is reused rather than allocated per call;
• TextMeasure::fit_prefix is a single xy_to_index query instead of the trait’s default binary search, so finding a wrap point costs one shaping pass rather than log n of them;
• a small cache keyed on (text, style) short-circuits the repeat measurements that wrapping produces for the same run.

Structs

PangoMeasure