TerrainData.UpdateDirtyRegion

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public void UpdateDirtyRegion (int x, int y, int width, int height, bool syncHeightmapTextureImmediately);

Parameters

xStart X position of the dirty heightmap region.
yStart Y position of the dirty heightmap region.
widthWidth of the the dirty heightmap region.
heightWidth of the the dirty heightmap region.
syncHeightmapTextureImmediatelyUpdate immediately, instead of deferring the update.

Description

Triggers an update to integrate modifications done to the heightmap outside of unity.

Invoke this whenever custom custom terrain heightmap paint tools modify the heightmap to let Unity integrate the changes (update collision, physics, etc ).