On Sun, 24 May 2015 01:55:30 -0700, David Kastrup <d...@gnu.org> wrote:
Anyway: how do impure functions reference (and trigger?) line breaks?
Non-'pure' functions reference line-breaks very indirectly. Spanners are broken into two or more grobs at line-breaking, so their functions work on the split Grobs that have a line-break column as a bound. I would have to trace to find the path whereby functions trigger line-breaking. I think the path is when the Y-extent of a Grob depends on the Y-extent of a VerticalAxisGroup. The pure version of the VerticalAxisGroup.Y-extent uses functions like rest_of_line_pure_height(,start,end) while the non-pure version ends up calling generic_group_extent(), which I suspect eventually calls the line-breaker. The facility for any 'pure' estimate of a property to depend on the start/end columns seems to have started with the *_of_line_pure_height() of VerticalAxisGroups. I cannot think of any other object for which they are used. The 'start'/'end' parameters are passed down the call stack, so if a 'pure' property depends ultimately on the Y-extent of a VerticalAxisGroup, it would need a sensible start/end pair; I do not know of a case where the 'pure' call-chains for properties of Items (as opposed to Spanners) ask for VerticalAxisGroup dimensions. Conceptually, the height of the arc of a slur could be estimated for a potential line-breaking, but that has not been implemented. If in the future we implement that, it seems that the control logic that is evaluating potential line-breaks would need to provide start/end information, or better the horizontal positions of the slur bounds, to the height-estimator for the Slur; I cannot imagine a way for Slur to seek out the potential line-breaks. But I think we can remove the 'start'/'end' parameters from 'pure' functions for Items. Items have a 'pure' version of their functions as a way to promise that these functions *not* depend on line-breaking. _______________________________________________ lilypond-devel mailing list lilypond-devel@gnu.org https://lists.gnu.org/mailman/listinfo/lilypond-devel
