# Copyright 2025 Stability AI, The HuggingFace Team and The InstantX Team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import Any, Dict, List, Optional, Tuple, Union
import torch
import torch.nn as nn
from ...configuration_utils import ConfigMixin, register_to_config
from ...loaders import FromOriginalModelMixin, PeftAdapterMixin, SD3Transformer2DLoadersMixin
from ...utils import USE_PEFT_BACKEND, logging, scale_lora_layers, unscale_lora_layers
from ...utils.torch_utils import maybe_allow_in_graph
from ..attention import FeedForward, JointTransformerBlock
from ..attention_processor import (
Attention,
AttentionProcessor,
FusedJointAttnProcessor2_0,
JointAttnProcessor2_0,
)
from ..embeddings import CombinedTimestepTextProjEmbeddings, PatchEmbed
from ..modeling_outputs import Transformer2DModelOutput
from ..modeling_utils import ModelMixin
from ..normalization import AdaLayerNormContinuous, AdaLayerNormZero
logger = logging.get_logger(__name__) # pylint: disable=invalid-name
@maybe_allow_in_graph
class SD3SingleTransformerBlock(nn.Module):
def __init__(
self,
dim: int,
num_attention_heads: int,
attention_head_dim: int,
):
super().__init__()
self.norm1 = AdaLayerNormZero(dim)
self.attn = Attention(
query_dim=dim,
dim_head=attention_head_dim,
heads=num_attention_heads,
out_dim=dim,
bias=True,
processor=JointAttnProcessor2_0(),
eps=1e-6,
)
self.norm2 = nn.LayerNorm(dim, elementwise_affine=False, eps=1e-6)
self.ff = FeedForward(dim=dim, dim_out=dim, activation_fn="gelu-approximate")
def forward(self, hidden_states: torch.Tensor, temb: torch.Tensor):
# 1. Attention
norm_hidden_states, gate_msa, shift_mlp, scale_mlp, gate_mlp = self.norm1(hidden_states, emb=temb)
attn_output = self.attn(hidden_states=norm_hidden_states, encoder_hidden_states=None)
attn_output = gate_msa.unsqueeze(1) * attn_output
hidden_states = hidden_states + attn_output
# 2. Feed Forward
norm_hidden_states = self.norm2(hidden_states)
norm_hidden_states = norm_hidden_states * (1 + scale_mlp.unsqueeze(1)) + shift_mlp.unsqueeze(1)
ff_output = self.ff(norm_hidden_states)
ff_output = gate_mlp.unsqueeze(1) * ff_output
hidden_states = hidden_states + ff_output
return hidden_states
class SD3Transformer2DModel(
ModelMixin, ConfigMixin, PeftAdapterMixin, FromOriginalModelMixin, SD3Transformer2DLoadersMixin
):
"""
The Transformer model introduced in [Stable Diffusion 3](https://huggingface.co/papers/2403.03206).
Parameters:
sample_size (`int`, defaults to `128`):
The width/height of the latents. This is fixed during training since it is used to learn a number of
position embeddings.
patch_size (`int`, defaults to `2`):
Patch size to turn the input data into small patches.
in_channels (`int`, defaults to `16`):
The number of latent channels in the input.
num_layers (`int`, defaults to `18`):
The number of layers of transformer blocks to use.
attention_head_dim (`int`, defaults to `64`):
The number of channels in each head.
num_attention_heads (`int`, defaults to `18`):
The number of heads to use for multi-head attention.
joint_attention_dim (`int`, defaults to `4096`):
The embedding dimension to use for joint text-image attention.
caption_projection_dim (`int`, defaults to `1152`):
The embedding dimension of caption embeddings.
pooled_projection_dim (`int`, defaults to `2048`):
The embedding dimension of pooled text projections.
out_channels (`int`, defaults to `16`):
The number of latent channels in the output.
pos_embed_max_size (`int`, defaults to `96`):
The maximum latent height/width of positional embeddings.
dual_attention_layers (`Tuple[int, ...]`, defaults to `()`):
The number of dual-stream transformer blocks to use.
qk_norm (`str`, *optional*, defaults to `None`):
The normalization to use for query and key in the attention layer. If `None`, no normalization is used.
"""
_supports_gradient_checkpointing = True
_no_split_modules = ["JointTransformerBlock"]
_skip_layerwise_casting_patterns = ["pos_embed", "norm"]
@register_to_config
def __init__(
self,
sample_size: int = 128,
patch_size: int = 2,
in_channels: int = 16,
num_layers: int = 18,
attention_head_dim: int = 64,
num_attention_heads: int = 18,
joint_attention_dim: int = 4096,
caption_projection_dim: int = 1152,
pooled_projection_dim: int = 2048,
out_channels: int = 16,
pos_embed_max_size: int = 96,
dual_attention_layers: Tuple[
int, ...
] = (), # () for sd3.0; (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) for sd3.5
qk_norm: Optional[str] = None,
):
super().__init__()
self.out_channels = out_channels if out_channels is not None else in_channels
self.inner_dim = num_attention_heads * attention_head_dim
self.pos_embed = PatchEmbed(
height=sample_size,
width=sample_size,
patch_size=patch_size,
in_channels=in_channels,
embed_dim=self.inner_dim,
pos_embed_max_size=pos_embed_max_size, # hard-code for now.
)
self.time_text_embed = CombinedTimestepTextProjEmbeddings(
embedding_dim=self.inner_dim, pooled_projection_dim=pooled_projection_dim
)
self.context_embedder = nn.Linear(joint_attention_dim, caption_projection_dim)
self.transformer_blocks = nn.ModuleList(
[
JointTransformerBlock(
dim=self.inner_dim,
num_attention_heads=num_attention_heads,
attention_head_dim=attention_head_dim,
context_pre_only=i == num_layers - 1,
qk_norm=qk_norm,
use_dual_attention=True if i in dual_attention_layers else False,
)
for i in range(num_layers)
]
)
self.norm_out = AdaLayerNormContinuous(self.inner_dim, self.inner_dim, elementwise_affine=False, eps=1e-6)
self.proj_out = nn.Linear(self.inner_dim, patch_size * patch_size * self.out_channels, bias=True)
self.gradient_checkpointing = False
# Copied from diffusers.models.unets.unet_3d_condition.UNet3DConditionModel.enable_forward_chunking
def enable_forward_chunking(self, chunk_size: Optional[int] = None, dim: int = 0) -> None:
"""
Sets the attention processor to use [feed forward
chunking](https://huggingface.co/blog/reformer#2-chunked-feed-forward-layers).
Parameters:
chunk_size (`int`, *optional*):
The chunk size of the feed-forward layers. If not specified, will run feed-forward layer individually
over each tensor of dim=`dim`.
dim (`int`, *optional*, defaults to `0`):
The dimension over which the feed-forward computation should be chunked. Choose between dim=0 (batch)
or dim=1 (sequence length).
"""
if dim not in [0, 1]:
raise ValueError(f"Make sure to set `dim` to either 0 or 1, not {dim}")
# By default chunk size is 1
chunk_size = chunk_size or 1
def fn_recursive_feed_forward(module: torch.nn.Module, chunk_size: int, dim: int):
if hasattr(module, "set_chunk_feed_forward"):
module.set_chunk_feed_forward(chunk_size=chunk_size, dim=dim)
for child in module.children():
fn_recursive_feed_forward(child, chunk_size, dim)
for module in self.children():
fn_recursive_feed_forward(module, chunk_size, dim)
# Copied from diffusers.models.unets.unet_3d_condition.UNet3DConditionModel.disable_forward_chunking
def disable_forward_chunking(self):
def fn_recursive_feed_forward(module: torch.nn.Module, chunk_size: int, dim: int):
if hasattr(module, "set_chunk_feed_forward"):
module.set_chunk_feed_forward(chunk_size=chunk_size, dim=dim)
for child in module.children():
fn_recursive_feed_forward(child, chunk_size, dim)
for module in self.children():
fn_recursive_feed_forward(module, None, 0)
@property
# Copied from diffusers.models.unets.unet_2d_condition.UNet2DConditionModel.attn_processors
def attn_processors(self) -> Dict[str, AttentionProcessor]:
r"""
Returns:
`dict` of attention processors: A dictionary containing all attention processors used in the model with
indexed by its weight name.
"""
# set recursively
processors = {}
def fn_recursive_add_processors(name: str, module: torch.nn.Module, processors: Dict[str, AttentionProcessor]):
if hasattr(module, "get_processor"):
processors[f"{name}.processor"] = module.get_processor()
for sub_name, child in module.named_children():
fn_recursive_add_processors(f"{name}.{sub_name}", child, processors)
return processors
for name, module in self.named_children():
fn_recursive_add_processors(name, module, processors)
return processors
# Copied from diffusers.models.unets.unet_2d_condition.UNet2DConditionModel.set_attn_processor
def set_attn_processor(self, processor: Union[AttentionProcessor, Dict[str, AttentionProcessor]]):
r"""
Sets the attention processor to use to compute attention.
Parameters:
processor (`dict` of `AttentionProcessor` or only `AttentionProcessor`):
The instantiated processor class or a dictionary of processor classes that will be set as the processor
for **all** `Attention` layers.
If `processor` is a dict, the key needs to define the path to the corresponding cross attention
processor. This is strongly recommended when setting trainable attention processors.
"""
count = len(self.attn_processors.keys())
if isinstance(processor, dict) and len(processor) != count:
raise ValueError(
f"A dict of processors was passed, but the number of processors {len(processor)} does not match the"
f" number of attention layers: {count}. Please make sure to pass {count} processor classes."
)
def fn_recursive_attn_processor(name: str, module: torch.nn.Module, processor):
if hasattr(module, "set_processor"):
if not isinstance(processor, dict):
module.set_processor(processor)
else:
module.set_processor(processor.pop(f"{name}.processor"))
for sub_name, child in module.named_children():
fn_recursive_attn_processor(f"{name}.{sub_name}", child, processor)
for name, module in self.named_children():
fn_recursive_attn_processor(name, module, processor)
# Copied from diffusers.models.unets.unet_2d_condition.UNet2DConditionModel.fuse_qkv_projections with FusedAttnProcessor2_0->FusedJointAttnProcessor2_0
def fuse_qkv_projections(self):
"""
Enables fused QKV projections. For self-attention modules, all projection matrices (i.e., query, key, value)
are fused. For cross-attention modules, key and value projection matrices are fused.
This API is 🧪 experimental.
"""
self.original_attn_processors = None
for _, attn_processor in self.attn_processors.items():
if "Added" in str(attn_processor.__class__.__name__):
raise ValueError("`fuse_qkv_projections()` is not supported for models having added KV projections.")
self.original_attn_processors = self.attn_processors
for module in self.modules():
if isinstance(module, Attention):
module.fuse_projections(fuse=True)
self.set_attn_processor(FusedJointAttnProcessor2_0())
# Copied from diffusers.models.unets.unet_2d_condition.UNet2DConditionModel.unfuse_qkv_projections
def unfuse_qkv_projections(self):
"""Disables the fused QKV projection if enabled.
This API is 🧪 experimental.
"""
if self.original_attn_processors is not None:
self.set_attn_processor(self.original_attn_processors)
def forward(
self,
hidden_states: torch.Tensor,
encoder_hidden_states: torch.Tensor = None,
pooled_projections: torch.Tensor = None,
timestep: torch.LongTensor = None,
block_controlnet_hidden_states: List = None,
joint_attention_kwargs: Optional[Dict[str, Any]] = None,
return_dict: bool = True,
skip_layers: Optional[List[int]] = None,
) -> Union[torch.Tensor, Transformer2DModelOutput]:
"""
The [`SD3Transformer2DModel`] forward method.
Args:
hidden_states (`torch.Tensor` of shape `(batch size, channel, height, width)`):
Input `hidden_states`.
encoder_hidden_states (`torch.Tensor` of shape `(batch size, sequence_len, embed_dims)`):
Conditional embeddings (embeddings computed from the input conditions such as prompts) to use.
pooled_projections (`torch.Tensor` of shape `(batch_size, projection_dim)`):
Embeddings projected from the embeddings of input conditions.
timestep (`torch.LongTensor`):
Used to indicate denoising step.
block_controlnet_hidden_states (`list` of `torch.Tensor`):
A list of tensors that if specified are added to the residuals of transformer blocks.
joint_attention_kwargs (`dict`, *optional*):
A kwargs dictionary that if specified is passed along to the `AttentionProcessor` as defined under
`self.processor` in
[diffusers.models.attention_processor](https://github.com/huggingface/diffusers/blob/main/src/diffusers/models/attention_processor.py).
return_dict (`bool`, *optional*, defaults to `True`):
Whether or not to return a [`~models.transformer_2d.Transformer2DModelOutput`] instead of a plain
tuple.
skip_layers (`list` of `int`, *optional*):
A list of layer indices to skip during the forward pass.
Returns:
If `return_dict` is True, an [`~models.transformer_2d.Transformer2DModelOutput`] is returned, otherwise a
`tuple` where the first element is the sample tensor.
"""
if joint_attention_kwargs is not None:
joint_attention_kwargs = joint_attention_kwargs.copy()
lora_scale = joint_attention_kwargs.pop("scale", 1.0)
else:
lora_scale = 1.0
if USE_PEFT_BACKEND:
# weight the lora layers by setting `lora_scale` for each PEFT layer
scale_lora_layers(self, lora_scale)
else:
if joint_attention_kwargs is not None and joint_attention_kwargs.get("scale", None) is not None:
logger.warning(
"Passing `scale` via `joint_attention_kwargs` when not using the PEFT backend is ineffective."
)
height, width = hidden_states.shape[-2:]
hidden_states = self.pos_embed(hidden_states) # takes care of adding positional embeddings too.
temb = self.time_text_embed(timestep, pooled_projections)
encoder_hidden_states = self.context_embedder(encoder_hidden_states)
if joint_attention_kwargs is not None and "ip_adapter_image_embeds" in joint_attention_kwargs:
ip_adapter_image_embeds = joint_attention_kwargs.pop("ip_adapter_image_embeds")
ip_hidden_states, ip_temb = self.image_proj(ip_adapter_image_embeds, timestep)
joint_attention_kwargs.update(ip_hidden_states=ip_hidden_states, temb=ip_temb)
for index_block, block in enumerate(self.transformer_blocks):
# Skip specified layers
is_skip = True if skip_layers is not None and index_block in skip_layers else False
if torch.is_grad_enabled() and self.gradient_checkpointing and not is_skip:
encoder_hidden_states, hidden_states = self._gradient_checkpointing_func(
block,
hidden_states,
encoder_hidden_states,
temb,
joint_attention_kwargs,
)
elif not is_skip:
encoder_hidden_states, hidden_states = block(
hidden_states=hidden_states,
encoder_hidden_states=encoder_hidden_states,
temb=temb,
joint_attention_kwargs=joint_attention_kwargs,
)
# controlnet residual
if block_controlnet_hidden_states is not None and block.context_pre_only is False:
interval_control = len(self.transformer_blocks) / len(block_controlnet_hidden_states)
hidden_states = hidden_states + block_controlnet_hidden_states[int(index_block / interval_control)]
hidden_states = self.norm_out(hidden_states, temb)
hidden_states = self.proj_out(hidden_states)
# unpatchify
patch_size = self.config.patch_size
height = height // patch_size
width = width // patch_size
hidden_states = hidden_states.reshape(
shape=(hidden_states.shape[0], height, width, patch_size, patch_size, self.out_channels)
)
hidden_states = torch.einsum("nhwpqc->nchpwq", hidden_states)
output = hidden_states.reshape(
shape=(hidden_states.shape[0], self.out_channels, height * patch_size, width * patch_size)
)
if USE_PEFT_BACKEND:
# remove `lora_scale` from each PEFT layer
unscale_lora_layers(self, lora_scale)
if not return_dict:
return (output,)
return Transformer2DModelOutput(sample=output)