Fixed incorrect loading of chunks near terrain borders with Clipbox

doc/source/changelog.md

@@ -22,6 +22,7 @@ Primarily developped with Godot 4.3.
     - `VoxelLodTerrain`:
         - Fixed potential crash when when using the Clipbox streaming system with threaded update (thanks to lenesxy, issue #692)
         - Fixed blocks were saved with incorrect LOD index when they get unloaded using Clipbox, leading to holes and mismatched terrain (#691)
+        - Fixed incorrect loading of chunks near terrain borders when viewers are far away from bounds, when using the Clipbox streaming system
     - `VoxelTerrain`: edits and copies across fixed bounds no longer behave as if terrain generates beyond (was causing "walls" to appear).
     - `VoxelGeneratorGraph`: fix wrong values when using `OutputWeight` with optimized execution map enabled, when weights are determined to be locally constant
     - `VoxelMesherTransvoxel`: revert texturing logic that attempted to prevent air voxels from contributing, but was lowering quality. It is now optional as an experimental property.

terrain/variable_lod/voxel_lod_terrain_update_clipbox_streaming.cpp

@@ -266,8 +266,6 @@ void process_viewers(
 				const int lod_mesh_block_size_po2 = volume_settings.mesh_block_size_po2 + lod_index;
 				const int lod_mesh_block_size = 1 << lod_mesh_block_size_po2;
 
-				const Box3i volume_bounds_in_mesh_blocks = volume_bounds_in_voxels.downscaled(lod_mesh_block_size);
-
 				const Vector3i ld = get_relative_lod_distance_in_chunks(
 						lod_index,
 						lod_count,
@@ -301,12 +299,19 @@ void process_viewers(
 					new_mesh_box = enforce_neighboring_rule(new_mesh_box, child_box, even_coordinates_required);
 				}
 
-				// Clip last
-				new_mesh_box.clip(volume_bounds_in_mesh_blocks);
-
 				paired_viewer.state.mesh_box_per_lod[lod_index] = new_mesh_box;
 			}
 
+			// Clip all mesh boxes in a second pass, because `enforce_neighboring_rule` depends on the child LOD box
+			for (unsigned int lod_index = 0; lod_index < lod_count; ++lod_index) {
+				const int lod_mesh_block_size_po2 = volume_settings.mesh_block_size_po2 + lod_index;
+				const int lod_mesh_block_size = 1 << lod_mesh_block_size_po2;
+				const Box3i volume_bounds_in_mesh_blocks = volume_bounds_in_voxels.downscaled(lod_mesh_block_size);
+
+				Box3i &box = paired_viewer.state.mesh_box_per_lod[lod_index];
+				box.clip(volume_bounds_in_mesh_blocks);
+			}
+
 			// TODO We should have a flag server side to force data boxes to be based on mesh boxes, even though the
 			// server might not actually need meshes. That would help the server to provide data chunks to clients,
 			// which need them for visual meshes