Computes the transitive closure of glyphs needed for a specified input buffer under the given font and feature list.
The closure is computed as a set, not as a list.
| font |
Font to work upon |
| buffer |
The input buffer to compute from |
| features |
The features enabled on the buffer |
| glyphs |
The Set set of glyphs comprising the transitive closure of the query |
| num_features |
The number of features enabled on the buffer |