Some path searches, using PathSearch, were created directly at the callsite rather than using the pathfinder trait. This means some searches did not not benefit from the performance checks done in the pathfinder trait. It also means the pathfinder trait was not responsible for all pathing done in the game. Fix this with the following changes:
- Create a sensible shape for the IPathFinder interface and promote it to a trait interface, allowing theoretical replacements of the implementation. Ensure none of the concrete classes in OpenRA.Mods.Common.Pathfinder are exposed in the interface to ensure this is possible.
- Update the PathFinder class to implement the interface, and update several callsites manually running pathfinding code to instead call the IPathFinder interface.
- Overall, this allows any implementation of the IPathFinder interface to intercept and control all path searching performed by the game. Previously some searches would not have used it, and no alternate implementations were possible as the existing implementation was hardcoded into the interface shape.
Additionally:
- Move the responsibility of finding paths on completed path searches from pathfinder to path search, which is a more sensible location.
- Clean up the pathfinder pre-search optimizations.
- When a path search is being performed the path search will not attempt route to inaccessible cells, so domain index checks to avoid inaccessible cells in the search predicate are redundant and can be removed.
- DomainIndex is a required world trait, so we don't need to use TraitOrDefault and therefore can avoid dealing with the null case.
The existing APIs surfaces for pathfinding are in a wonky shape. We rearrange various responsibilities to better locations and simplify some abstractions that aren't providing value.
- IPathSearch, BasePathSearch and PathSearch are combined into only PathSearch. Its role is now to run a search space over a graph, maintaining the open queue and evaluating the provided heuristic function. The builder-like methods (WithHeuristic, Reverse, FromPoint, etc) are removed in favour of optional parameters in static creation methods. This removes confusion between the builder-aspect and the search function itself. It also becomes responsible for applying the heuristic weight to the heuristic. This fixes an issue where an externally provided heuristic ignored the weighting adjustment, as previously the weight was baked into the default heuristic only.
- Reduce the IGraph interface to the concepts of nodes and edges. Make it non-generic as it is specifically for pathfinding, and rename to IPathGraph accordingly. This is sufficient for a PathSearch to perform a search over any given IGraph. The various customization options are concrete properties of PathGraph only.
- PathFinder does not need to deal with disposal of the search/graph, that is the caller's responsibility.
- Remove CustomBlock from PathGraph as it was unused.
- Remove FindUnitPathToRange as it was unused.
- Use PathFinder.NoPath as the single helper to represent no/empty paths.
Each successive value of BlockedByActor is a superset of the previous value. Having a mixed up order of values in PathSearchOrder is not useful.
In the previous ordering, if a search for Immovable failed to find a path, it would then attempt Stationary. However Stationary is *more* restrictive then Immovable. If Immovable failed, there is no way Stationary could succeed. This means the search for Stationary is wasted effort.
In the fixed ordering, we try Stationary first. In the fixed ordering there are no pointless searches. Every search might succeed where the previous one failed and is therefore useful to try.
If progress == Distance, we must not move again on the same tick,
but still 'return true' to avoid losing a tick in the case
when this is the last Move tick followed by a different activity
(or a new queued Move, for example via waypoints).
There were 2 issues at work here, both when progress
would overshoot Distance (which is the usual case,
rather than the exception):
- the overshot progress was passed on by MoveFirstHalf, however
OnComplete would make the next MovePart start ticking the
same tick on which the old MovePart reached Distance,
but move by carryoverProgress +(!!!) terrain speed instead of moving
by just the left-over carryoverProgress.
- MoveSecondHalf would not pass any overshot progress to the
next MoveFirstHalf queued by parent Move, leading to
the next MoveFirstHalf performing a full-speed move the same tick
MoveSecondHalf finished its last move.
InnerActivity and UpdateCenterLocation made this
overly complex and hard to read & debug.
This also fixes a bug that would make an outdated
facing being passed during OnComplete (because
InnerActivity was cached before UpdateCenterLocation
could set the correct final facing).
While they may be only 'visual' in terms of influence/cell grid,
they all do update CenterPosition, which is essentially the
actual world position of the actor.
'Visual' would imply that it only affects the position where the
actor is drawn, which is inaccurate.
Furthermore, using the term 'Visual' here would make
naming future methods/properties related to visual interpolation
unnecessarily complicated, because that's where we might
need a real 'Visual(Only)Position'.
While individual trait look-ups may be cheap,
if a large army that is currently standing still gets
its first move-including order, the look-ups of dozens
or even hundreds of actors may happen on the same tick.
Therefore this may help reducing that first-order lag spike,
at least a little bit.
