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trellis/modules/sparse/spatial.py

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+from typing import *
+import torch
+import torch.nn as nn
+from . import SparseTensor
+
+__all__ = [
+    'SparseDownsample',
+    'SparseUpsample',
+    'SparseSubdivide'
+]
+
+
+class SparseDownsample(nn.Module):
+    """
+    Downsample a sparse tensor by a factor of `factor`.
+    Implemented as average pooling.
+    """
+    def __init__(self, factor: Union[int, Tuple[int, ...], List[int]]):
+        super(SparseDownsample, self).__init__()
+        self.factor = tuple(factor) if isinstance(factor, (list, tuple)) else factor
+
+    def forward(self, input: SparseTensor) -> SparseTensor:
+        DIM = input.coords.shape[-1] - 1
+        factor = self.factor if isinstance(self.factor, tuple) else (self.factor,) * DIM
+        assert DIM == len(factor), 'Input coordinates must have the same dimension as the downsample factor.'
+
+        coord = list(input.coords.unbind(dim=-1))
+        for i, f in enumerate(factor):
+            coord[i+1] = coord[i+1] // f
+
+        MAX = [coord[i+1].max().item() + 1 for i in range(DIM)]
+        OFFSET = torch.cumprod(torch.tensor(MAX[::-1]), 0).tolist()[::-1] + [1]
+        code = sum([c * o for c, o in zip(coord, OFFSET)])
+        code, idx = code.unique(return_inverse=True)
+
+        new_feats = torch.scatter_reduce(
+            torch.zeros(code.shape[0], input.feats.shape[1], device=input.feats.device, dtype=input.feats.dtype),
+            dim=0,
+            index=idx.unsqueeze(1).expand(-1, input.feats.shape[1]),
+            src=input.feats,
+            reduce='mean'
+        )
+        new_coords = torch.stack(
+            [code // OFFSET[0]] +
+            [(code // OFFSET[i+1]) % MAX[i] for i in range(DIM)],
+            dim=-1
+        )
+        out = SparseTensor(new_feats, new_coords, input.shape,)
+        out._scale = tuple([s // f for s, f in zip(input._scale, factor)])
+        out._spatial_cache = input._spatial_cache
+
+        out.register_spatial_cache(f'upsample_{factor}_coords', input.coords)
+        out.register_spatial_cache(f'upsample_{factor}_layout', input.layout)
+        out.register_spatial_cache(f'upsample_{factor}_idx', idx)
+
+        return out
+
+
+class SparseUpsample(nn.Module):
+    """
+    Upsample a sparse tensor by a factor of `factor`.
+    Implemented as nearest neighbor interpolation.
+    """
+    def __init__(self, factor: Union[int, Tuple[int, int, int], List[int]]):
+        super(SparseUpsample, self).__init__()
+        self.factor = tuple(factor) if isinstance(factor, (list, tuple)) else factor
+
+    def forward(self, input: SparseTensor) -> SparseTensor:
+        DIM = input.coords.shape[-1] - 1
+        factor = self.factor if isinstance(self.factor, tuple) else (self.factor,) * DIM
+        assert DIM == len(factor), 'Input coordinates must have the same dimension as the upsample factor.'
+
+        new_coords = input.get_spatial_cache(f'upsample_{factor}_coords')
+        new_layout = input.get_spatial_cache(f'upsample_{factor}_layout')
+        idx = input.get_spatial_cache(f'upsample_{factor}_idx')
+        if any([x is None for x in [new_coords, new_layout, idx]]):
+            raise ValueError('Upsample cache not found. SparseUpsample must be paired with SparseDownsample.')
+        new_feats = input.feats[idx]
+        out = SparseTensor(new_feats, new_coords, input.shape, new_layout)
+        out._scale = tuple([s * f for s, f in zip(input._scale, factor)])
+        out._spatial_cache = input._spatial_cache
+        return out
+    
+class SparseSubdivide(nn.Module):
+    """
+    Upsample a sparse tensor by a factor of `factor`.
+    Implemented as nearest neighbor interpolation.
+    """
+    def __init__(self):
+        super(SparseSubdivide, self).__init__()
+
+    def forward(self, input: SparseTensor) -> SparseTensor:
+        DIM = input.coords.shape[-1] - 1
+        # upsample scale=2^DIM
+        n_cube = torch.ones([2] * DIM, device=input.device, dtype=torch.int)
+        n_coords = torch.nonzero(n_cube)
+        n_coords = torch.cat([torch.zeros_like(n_coords[:, :1]), n_coords], dim=-1)
+        factor = n_coords.shape[0]
+        assert factor == 2 ** DIM
+        # print(n_coords.shape)
+        new_coords = input.coords.clone()
+        new_coords[:, 1:] *= 2
+        new_coords = new_coords.unsqueeze(1) + n_coords.unsqueeze(0).to(new_coords.dtype)
+        
+        new_feats = input.feats.unsqueeze(1).expand(input.feats.shape[0], factor, *input.feats.shape[1:])
+        out = SparseTensor(new_feats.flatten(0, 1), new_coords.flatten(0, 1), input.shape)
+        out._scale = input._scale * 2
+        out._spatial_cache = input._spatial_cache
+        return out
+