ViewLegendsTask

`construct.view.legends`: the field legends of the viewport, as a person sees them (construct-fea-solve §FEO-1).

In the namespace construct::opal. Declared in src/libs/libconstruct/construct/opal/ViewLegendsTask.hpp.

Detailed description

Read only. It runs the two functions the corner HUD of the shell runs, construct::model::collectLegendInputs() and construct::model::groupFieldLegends(), on the document the call names, so a plan sees the legends a person sees: one entry per legend that shows, at most three, with its items, field, label, unit, range, colormap, clamp marks and out-of-date state, and `moreItems`, the colored items whose legend does not show. Since field-presentation phase 3b also how the colors read: bands, the out-of-range rule and colors, the scale, the no-data swatch, the true maximum and the caption lines (§FVO-3).

An item shows a legend when its field's values are built. The first call after a change of field can start that build on the thread pool and list no legend for the item; a later call lists it, as the viewport shows it when the values land.

Not FEM-guarded: every mesh and tet item can show a field (quality, volume, depth, the dihedral angle) with no solver in the build.