How do I construct a Bounds Query for 3D Simplex Noise?
[This is more or less a follow-up to my last question]
Simply put, for an arbitrary octree node (cube) in my volume (a section of Unity3d world space), I am trying to find out whether there is a surface inside the octree node (to determine if I need to subdivide my octree node). As explained in the other question, I cannot rely on edge-crossings to detect if a node contains a surface or not. Right now, I query each Vector3 integer coordinate in my volume (appropriately scaled by ~1/50) for a simplex noise value.
I was directed to bounds queries, where instead of querying for a specific point by supplying specific coordinates, I query for a
[min,max] of the function in a certain volume (my octree node). If
min > 0 or
max < 0, I need not subdivide, because the surface is outside my node (the surface intersects edges between vertices with different polarity/signs).
What (I think) I understand so far:
- At every simplex vertex, the value is
0. This means that my minimum is not greater than 0, and my maximum is not less than 0. Turns out, because of my scaling, a single octave of simplex noise usually just puts 2 simplex vertices in my volume. Does this mean that my bounds query will require I subdivide every node that contains one of these simplex vertices? This is obviously wrong, else I would be subdividing infinitely...
- If I do not have any simplex vertex in my node, I still have to find the vertices' unit vectors of the simplices my node exists in. Then, somehow, I decide on a min/max. I suppose, it would come down to the nature of the simplices I am in...If they both give positive/negative values, then my bounds query would pass, and I wouldn't need to subdivide...right? But how do I calculate this?
- To construct the bounds query, I must find the pseudo-random unit vector assigned to each simplex vertex found in my node. This allows me to view the range of possible values in each simplex found in the node.
(I hope that all wasn't too confusing)
Despite/Because all that, I can't for the life of me think up any algorithm. What am I missing?
If there are any resources on this, please point me to them! I've googled about every keyword-loaded phrase I can come up with, but found nothing.