AStarGrid2D allow_partial_path returning no path when there should be about godot HOT 4 OPEN

So while technically a disabled/solid point is part of the point list, if the end point is disabled (or "solid" for the AStarGrid2D class) _solve returns early which means even when asked to return the partial path the path is still an empty array as no actual pathfinding was done yet. You can see this early return here

https://github.com/godotengine/godot/blob/master/core/math/a_star_grid_2d.cpp#L453

The original issue that the partial path implementation was for was for non-disabled points that are in the point list, finding a path close to those even if there are obstacles preventing a complete path. The picture from the original proposal (godotengine/godot-proposals#277) showcases that intention

I did not change/modify the early termination present when the destination is itself disabled, however I can see the merit in having this functionality too. The main issue is this change would, unless I dragged in the partial path option into the _solve function to modify the early termination (which could be done if desired), mean that even for users who are not desiring a partial return the extra "processing" would happen to find that partial path even though we would then discard that result and return the empty array.

This short circuit was added as part of #27506 when disabling points became an option, as it represents a much more performant way to temporarily add/remove points from pathfinding without having to actually run the more expensive add/remove point functions. I believe the specific part of having it in _solve was just for the optimization of not trying to pathfind when the destination was "invalid", though this is speculation on my part as the intention wasn't directly stated anywhere.

Curious to hear other's thoughts on it as well!

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I was personally caught out by this just now. The documentation of the current behaviour in the AStarGrid2D doc lead me to believe that it would find the closest non-solid tile to a solid tile. It's very understandable why this isn't the case upon reading into it, though!

That said, I do think it should be considered inside the _solve function, since it makes sense in my head for allow_partial_path to perform the way I originally thought it would. I'll work around it in the meantime!

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I found godotengine/godot-proposals#277 (comment) so it seems like I'm not alone with there being some confusion on how partial path is meant to work

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I found godotengine/godot-proposals#277 (comment) so it seems like I'm not alone with there being some confusion on how partial path is meant to work

#88047 description says:

Note: This will not return a partial path to a location not in the AStar point list, the destination point still has to be a point. This is especially helpful for games where points may become disconnected due to other points being disabled during play while still permitting a path that gets close to the destination point.

cc @theashtronaut

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