add LcmAdapter

This adds support for the condition scale embedding.
Also updates the UNet converter to support LCM.

scripts/conversion/convert_diffusers_unet.py

@@ -1,5 +1,6 @@
 import argparse
 from pathlib import Path
+from typing import Any
 
 import torch
 from diffusers import UNet2DConditionModel  # type: ignore
@@ -7,6 +8,7 @@ from torch import nn
 
 from refiners.fluxion.model_converter import ModelConverter
 from refiners.foundationals.latent_diffusion import SD1UNet, SDXLUNet
+from refiners.foundationals.latent_diffusion.stable_diffusion_xl.lcm import LcmAdapter
 
 
 class Args(argparse.Namespace):
@@ -28,9 +30,16 @@ def setup_converter(args: Args) -> ModelConverter:
     source_in_channels: int = source.config.in_channels  # type: ignore
     source_clip_embedding_dim: int = source.config.cross_attention_dim  # type: ignore
     source_has_time_ids: bool = source.config.addition_embed_type == "text_time"  # type: ignore
-    target = (
-        SDXLUNet(in_channels=source_in_channels) if source_has_time_ids else SD1UNet(in_channels=source_in_channels)
-    )
+    source_is_lcm: bool = source.config.time_cond_proj_dim is not None
+
+    if source_has_time_ids:
+        target = SDXLUNet(in_channels=source_in_channels)
+    else:
+        target = SD1UNet(in_channels=source_in_channels)
+
+    if source_is_lcm:
+        assert isinstance(target, SDXLUNet)
+        LcmAdapter(target=target).inject()
 
     x = torch.randn(1, source_in_channels, 32, 32)
     timestep = torch.tensor(data=[0])
@@ -45,9 +54,16 @@ def setup_converter(args: Args) -> ModelConverter:
         target.set_pooled_text_embedding(pooled_text_embedding=added_cond_kwargs["text_embeds"])
 
     target_args = (x,)
+
+    source_kwargs: dict[str, Any] = {}
+    if source_has_time_ids:
+        source_kwargs["added_cond_kwargs"] = added_cond_kwargs
+    if source_is_lcm:
+        source_kwargs["timestep_cond"] = torch.randn(1, source.config.time_cond_proj_dim)
+
     source_args = {
         "positional": (x, timestep, clip_text_embeddings),
-        "keyword": {"added_cond_kwargs": added_cond_kwargs} if source_has_time_ids else {},
+        "keyword": source_kwargs,
     }
 
     converter = ModelConverter(

src/refiners/foundationals/latent_diffusion/stable_diffusion_xl/lcm.py

@@ -0,0 +1,88 @@
+import math
+
+import torch
+
+import refiners.fluxion.layers as fl
+from refiners.fluxion.adapters.adapter import Adapter
+from refiners.fluxion.context import Contexts
+from refiners.foundationals.latent_diffusion.range_adapter import RangeEncoder
+from refiners.foundationals.latent_diffusion.stable_diffusion_xl.unet import SDXLUNet
+
+
+def compute_sinusoidal_embedding(
+    x: torch.Tensor,
+    embedding_dim: int,
+) -> torch.Tensor:
+    # Differences from compute_sinusoidal_embedding in RangeAdapter:
+    # - we concat [sin, cos], it does the opposite ([cos, sin])
+    # - we divide the exponent by half_dim - 1, it divides by half_dim
+
+    half_dim = embedding_dim // 2
+    # Note: it is important that this computation is done in float32.
+    # The result can be cast to lower precision later if necessary.
+    exponent = -math.log(10000) * torch.arange(start=0, end=half_dim, dtype=torch.float32, device=x.device)
+    exponent /= half_dim - 1
+    embedding = x.unsqueeze(1).float() * torch.exp(exponent).unsqueeze(0)
+    embedding = torch.cat([torch.sin(embedding), torch.cos(embedding)], dim=-1)
+
+    assert embedding.shape == (x.shape[0], embedding_dim)
+    return embedding
+
+
+class ResidualBlock(fl.Residual):
+    def __init__(
+        self,
+        in_channels: int,
+        out_channels: int,
+        device: torch.device | str | None = None,
+        dtype: torch.dtype | None = None,
+    ) -> None:
+        super().__init__(
+            fl.UseContext("lcm", "condition_scale_embedding"),
+            fl.Converter(),
+            fl.Linear(in_features=in_channels, out_features=out_channels, bias=False, device=device, dtype=dtype),
+        )
+
+
+class LcmAdapter(fl.Chain, Adapter[SDXLUNet]):
+    def __init__(
+        self,
+        target: SDXLUNet,
+        condition_scale_embedding_dim: int = 256,
+        condition_scale: float = 7.5,
+    ) -> None:
+        assert condition_scale_embedding_dim % 2 == 0
+        self.condition_scale_embedding_dim = condition_scale_embedding_dim
+        self.condition_scale = condition_scale
+        with self.setup_adapter(target):
+            super().__init__(target)
+
+    def init_context(self) -> Contexts:
+        return {"lcm": {"condition_scale_embedding": self.sinusoidal_embedding}}
+
+    @property
+    def sinusoidal_embedding(self) -> torch.Tensor:
+        return compute_sinusoidal_embedding(
+            torch.tensor([(self.condition_scale - 1) * 1000], device=self.device),
+            embedding_dim=self.condition_scale_embedding_dim,
+        )
+
+    def set_condition_scale(self, scale: float) -> None:
+        self.condition_scale = scale
+        self.set_context("lcm", {"condition_scale_embedding": self.sinusoidal_embedding})
+
+    def inject(self: "LcmAdapter", parent: fl.Chain | None = None) -> "LcmAdapter":
+        ra = self.target.ensure_find(RangeEncoder)
+        block = ResidualBlock(
+            in_channels=self.condition_scale_embedding_dim,
+            out_channels=ra.sinusoidal_embedding_dim,
+            device=self.target.device,
+            dtype=self.target.dtype,
+        )
+        ra.insert_before_type(fl.Linear, block)
+        return super().inject(parent)
+
+    def eject(self) -> None:
+        ra = self.target.ensure_find(RangeEncoder)
+        ra.remove(ra.ensure_find(ResidualBlock))
+        super().eject()