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Fix Transvoxel when the surface lines up with integer coordinates

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This commit is contained in:
Marc Gilleron 2022-03-19 22:45:12 +00:00
parent bf946db0ef
commit d4b1178d61
1 changed files with 15 additions and 8 deletions
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23
meshers/transvoxel/transvoxel.cpp
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@ -321,16 +321,23 @@ void build_regular_mesh(Span<const Sdf_T> sdf_data, TextureIndicesData texture_i
for (pos.x = min_pos.x; pos.x < max_pos.x; ++pos.x, data_index += block_size_with_padding.y) {
{
const bool s = sdf_data[data_index] < isolevel;
// The chosen comparison here is very important. This relates to case selections where 4 samples
// are equal to the isolevel and 4 others are above or below:
// In one of these two cases, there has to be a surface to extract, otherwise no surface will be
// allowed to appear if it happens to line up with integer coordinates.
// If we used `<` instead of `>`, it would appear to work, but would break those edge cases.
// `>` is chosen because it must match the comparison we do with case selection (in Transvoxel
// it is inverted).
const bool s = sdf_data[data_index] > isolevel;
if ( //
(sdf_data[data_index + n010] < isolevel) == s &&
(sdf_data[data_index + n100] < isolevel) == s &&
(sdf_data[data_index + n110] < isolevel) == s &&
(sdf_data[data_index + n001] < isolevel) == s &&
(sdf_data[data_index + n011] < isolevel) == s &&
(sdf_data[data_index + n101] < isolevel) == s &&
(sdf_data[data_index + n111] < isolevel) == s) {
(sdf_data[data_index + n010] > isolevel) == s &&
(sdf_data[data_index + n100] > isolevel) == s &&
(sdf_data[data_index + n110] > isolevel) == s &&
(sdf_data[data_index + n001] > isolevel) == s &&
(sdf_data[data_index + n011] > isolevel) == s &&
(sdf_data[data_index + n101] > isolevel) == s &&
(sdf_data[data_index + n111] > isolevel) == s) {
// Not crossing the isolevel, this cell won't produce any geometry.
// We must figure this out as fast as possible, because it will happen a lot.
continue;