These are the numbers I'm using for the planet in the video and below are estimates of how much uncompressed memory would be needed for a planet with these properties:
Patch Size (# vertices on a single patch edge): 33
Max Depth of Quad Tree: 5
Texture Size Per Patch: 128 x 128
Assuming I could use a single height map, normal map and tangent map and sample them by using geomipmapping:
16 bit height map memory = 6 faces x ((33 verts per patch x 2^(max depth + 1)) - (2^(max depth + 1) - 1))^2 x 2 (because 16 bit)
= 6 x ((33 x 64) - (64 - 1))^2 x 2
= 6 x (2049 x 2049) x 2
= 6 x 8,396,802
= 58,777,614 bytes
8 bit normal map memory = 6 faces x ((33 verts per patch x 2^(max depth + 1)) - (2^(max depth + 1) - 1))^2 x 3 (for x,y,z)
= 6 x (2049 x 2049) x 3
= 75,571,218 bytes
tangent map is the same size as normal map
128x128 textures memory: this is a summation for each level or you can just calculate the amount needed for the deepest level and multiply by 1/3rd for a ceiling estimate (same estimate used when doing mip mapping) because each level is one mip map level lower than the level below it.
= 6 faces x texture size x num patches at lowest level x num bytes per pixel
= 6 faces x (128 x 128) x (2^(max depth + 1))^2 x 3
= 6 x (128 x 128) x 4096 x 3
= 1,207,959,552 bytes
ceiling = 1,207,959,552 + (1,207,959,552 / 3) = 1,610,612,736 bytes
So the total is:
58,777,614 + 75,571,218 + 75,571,218 + 1,610,612,736
= 1,820,532,786 bytes
So just under 2 GB for a single planet and nothing else. While 2GB is not an unreasonable amount of RAM to ask a gaming rig to set aside these days it is still too much if you want to have a lot of other models, animations and textures loaded. That's why I've been working on resource management more than anything else.
I would like to allow the entire planet to be custom made and loaded from disk rather than just generated on the fly and I'd like to be able to support a combination of both. The idea is that a planet starts out randomly generated and then get's customized by the artist - this should work well in cases where you have a couple continents and the rest is ocean floor, or where you have a moon that is not customized at all. No reason for your artists to spend time on the ocean floor usually, and hopefully they can tweak the generation parameters to get close the the type of land formations they want.
Really, I could load the height map into memory and always generate the normals and tangents based on the height map. The textures would be too large to keep all in memory at once so I would still have to load/unload those as needed.
Alternately, I could scrap the whole texture per patch thing and go back to some blended texture pixel shader based on a blend map that is the same resolution as the height maps ( 6 x (2049 x 2049) x 8 layers = 201,523,248 bytes)