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Is BC4 good for distance field compression? Analysis follows...

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from what I know: no.

@sjb3d

has played w it if I remember right.

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and

We switched from BC4 to U8 to be able to render bricks directly. Need the precision for normals but also to keep shared texels identical for neighbouring bricks (we store 8^3 voxel corners to render 7^3 volume).

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and

So you used 8x8x8 tiles in volume texture, each representing 7x7x7 area (with single side borders)? How do you mipmap this? This is a now pow2 tile size. 9x9x9 tiles that represent 8x8x8 regions align perfectly to upper/lower mip level tiles.

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and

Yep texels are duplicated on all shared faces. Not sure what you mean about mip maps, bricks form an octree for level of detail, each octree node is 7 texels long, octree node corners line up with texel centres at all levels (so need 8^3 storage for each).

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and

In 2D, layout is like this (black: octree node bounds, blue: current node texels, red: top-left child node texels)

3:31 PM · Oct 17, 2020Twitter Web App

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and

Oh yes... if the leaf node represents a 7x7x7 region, then the parent of course represents 14x14x14 region (at half res) and the grandparent represents 28x28x28 region (at quarter res). Thus all nodes are 7x7x7 at 1 voxel border. This is better for GPU cache lines than 8x8x8+1.