pseudocode.txt

# Cross level merging

- Build multi map of potential matches for each node, up to a certain depth (1/2 of max by default)
- Add all nodes of level below the root to the list of nodes to check
- For every level
    - Rebuild multi-map if necessary (if depth of subtrees is smaller than those in multi-map)
    - For every node to check (that has not been eliminated yet)
        - For each other level higher up:
            - For each potential match
                - If equal through deep comparison
                    - Store correspondences for all nodes in the duplicate subtrees
        - If no match found
            - Add to list of nodes to check next
    - Update pointers of nodes in the level above
    - Update pointers of nodes in lower levels to nodes in this level

## Symmetric cross level merging

- Same, for each symmetry option:
    - Build match maps for each symmetry option
    - Deep comparison for each symmetry option
    - Also store symmetry option in correspondence
    
### -OR-
- Convert to SDAG
- Create multi-map of MirrorNode hashes
- The same as normal cross level merging


# Exploiting hidden geometry
1. Normal based
 - Voxels on the surface of a closed object only need to look right from the outside
 - The part of the nodes that lay inside of the surface can be changed as we please
2. Inside/outside based
 - Any node on the inside of a closed surface can be changed as we please
 
Question:
 - How to implement this
    1:
    - Store normal in each node in the SVO
    - When merging nodes, mark nodes as unusable if their normals differ greater than a threshold
    - 
    2:
    - Inner nodes: Do subtree comparisons, but ignore the children that are hidden
    - Leaf nodes:  Do child bit mask comparison, but ignore bits that are hidden
    
 - 

 ## Current status
 - Flood fill from a corner of the scene, marking all nodes on the outside with a bitmask in their parent
 - How to ignore the inside children during subtree comparison?
    - Single level merging: In the comparator of two nodes, take the AND of the outside masks, only compare those children
    - No straightforward compatibility with cross-level merging, since the hashes are precomputed
        - Could maybe pre-compute all hash combinations (2^8 match maps), which is O(256) time increase
    - Problem: Can't sort nodes anymore (so can't put them in a map)
        - Since the comparison between any two nodes is dynamic: ChildMask & OutsideMask
        - Therefore, single-level merging doesn't work in the way it is currently implemented
 
# Lossy compression:
 - Currently only in low levels, on nodes that are referenced infrequently
 - Todo: Noisiness of voxels and "create no holes, only fill them?"
 - Can also use noisiness indicator for fake detail using cycles
    - Wouldn't be useful for flat surfaces, but for organic material/smoke/particles