we can avoid the terrain sync completely in most cases #3103
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elsid
requested changes
Sep 15, 2021
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From the logic point of view this change is ok but need to fix comments. Benchmark I used for https://gitlab.com/OpenMW/openmw/-/merge_requests/1193 shows improvement. Flying over 21 cells doesn't cause more than 2 ms spent on terrain preloading in Scene::changeCellGrid vs 64 ms before.
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We can take elsid's commit 605cb8d further by avoiding the terrain sync completely in most cases. Currently in changeCellGrid we wait for a new preloading task to ensure the getPagedRefnums for the new active cells have been filled in by object paging. This is usually not necessary because we have already completed a preload in the past containing these active cells. With this PR we remember what we preloaded and skip the terrain sync if it is not needed.
How to test this PR:
[ ] Check that syncTerrainLoad will no longer be called in the usual case, moving slowly
[ ] Check that syncTerrainLoad will still be called in unusual cases, e.g. abruptly changing direction at high speed