Adds SV4D code

sgm/modules/diffusionmodules/util.py

@@ -17,6 +17,36 @@ import torch.nn as nn
 from einops import rearrange, repeat
 
 
+def get_alpha(
+    merge_strategy: str,
+    mix_factor: Optional[torch.Tensor],
+    image_only_indicator: torch.Tensor,
+    apply_sigmoid: bool = True,
+    is_attn: bool = False,
+) -> torch.Tensor:
+    if merge_strategy == "fixed" or merge_strategy == "learned":
+        alpha = mix_factor
+    elif merge_strategy == "learned_with_images":
+        alpha = torch.where(
+            image_only_indicator.bool(),
+            torch.ones(1, 1, device=image_only_indicator.device),
+            rearrange(mix_factor, "... -> ... 1"),
+        )
+        if is_attn:
+            alpha = rearrange(alpha, "b t -> (b t) 1 1")
+        else:
+            alpha = rearrange(alpha, "b t -> b 1 t 1 1")
+    elif merge_strategy == "fixed_with_images":
+        alpha = image_only_indicator
+        if is_attn:
+            alpha = rearrange(alpha, "b t -> (b t) 1 1")
+        else:
+            alpha = rearrange(alpha, "b t -> b 1 t 1 1")
+    else:
+        raise NotImplementedError
+    return torch.sigmoid(alpha) if apply_sigmoid else alpha
+
+    
 def make_beta_schedule(
     schedule,
     n_timestep,