# Copyright 2024 The HuggingFace 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, Optional, Union
import torch
from torch import nn
from ...configuration_utils import ConfigMixin, register_to_config
from ...utils import is_torch_version, logging
from ..attention import BasicTransformerBlock
from ..attention_processor import Attention, AttentionProcessor, FusedAttnProcessor2_0
from ..embeddings import PatchEmbed, PixArtAlphaTextProjection
from ..modeling_outputs import Transformer2DModelOutput
from ..modeling_utils import ModelMixin
from ..normalization import AdaLayerNormSingle
logger = logging.get_logger(__name__) # pylint: disable=invalid-name
class PixArtTransformer2DModel(ModelMixin, ConfigMixin):
r"""
A 2D Transformer model as introduced in PixArt family of models (https://arxiv.org/abs/2310.00426,
https://arxiv.org/abs/2403.04692).
Parameters:
num_attention_heads (int, optional, defaults to 16): The number of heads to use for multi-head attention.
attention_head_dim (int, optional, defaults to 72): The number of channels in each head.
in_channels (int, defaults to 4): The number of channels in the input.
out_channels (int, optional):
The number of channels in the output. Specify this parameter if the output channel number differs from the
input.
num_layers (int, optional, defaults to 28): The number of layers of Transformer blocks to use.
dropout (float, optional, defaults to 0.0): The dropout probability to use within the Transformer blocks.
norm_num_groups (int, optional, defaults to 32):
Number of groups for group normalization within Transformer blocks.
cross_attention_dim (int, optional):
The dimensionality for cross-attention layers, typically matching the encoder's hidden dimension.
attention_bias (bool, optional, defaults to True):
Configure if the Transformer blocks' attention should contain a bias parameter.
sample_size (int, defaults to 128):
The width of the latent images. This parameter is fixed during training.
patch_size (int, defaults to 2):
Size of the patches the model processes, relevant for architectures working on non-sequential data.
activation_fn (str, optional, defaults to "gelu-approximate"):
Activation function to use in feed-forward networks within Transformer blocks.
num_embeds_ada_norm (int, optional, defaults to 1000):
Number of embeddings for AdaLayerNorm, fixed during training and affects the maximum denoising steps during
inference.
upcast_attention (bool, optional, defaults to False):
If true, upcasts the attention mechanism dimensions for potentially improved performance.
norm_type (str, optional, defaults to "ada_norm_zero"):
Specifies the type of normalization used, can be 'ada_norm_zero'.
norm_elementwise_affine (bool, optional, defaults to False):
If true, enables element-wise affine parameters in the normalization layers.
norm_eps (float, optional, defaults to 1e-6):
A small constant added to the denominator in normalization layers to prevent division by zero.
interpolation_scale (int, optional): Scale factor to use during interpolating the position embeddings.
use_additional_conditions (bool, optional): If we're using additional conditions as inputs.
attention_type (str, optional, defaults to "default"): Kind of attention mechanism to be used.
caption_channels (int, optional, defaults to None):
Number of channels to use for projecting the caption embeddings.
use_linear_projection (bool, optional, defaults to False):
Deprecated argument. Will be removed in a future version.
num_vector_embeds (bool, optional, defaults to False):
Deprecated argument. Will be removed in a future version.
"""
_supports_gradient_checkpointing = True
_no_split_modules = ["BasicTransformerBlock", "PatchEmbed"]
@register_to_config
def __init__(
self,
num_attention_heads: int = 16,
attention_head_dim: int = 72,
in_channels: int = 4,
out_channels: Optional[int] = 8,
num_layers: int = 28,
dropout: float = 0.0,
norm_num_groups: int = 32,
cross_attention_dim: Optional[int] = 1152,
attention_bias: bool = True,
sample_size: int = 128,
patch_size: int = 2,
activation_fn: str = "gelu-approximate",
num_embeds_ada_norm: Optional[int] = 1000,
upcast_attention: bool = False,
norm_type: str = "ada_norm_single",
norm_elementwise_affine: bool = False,
norm_eps: float = 1e-6,
interpolation_scale: Optional[int] = None,
use_additional_conditions: Optional[bool] = None,
caption_channels: Optional[int] = None,
attention_type: Optional[str] = "default",
):
super().__init__()
# Validate inputs.
if norm_type != "ada_norm_single":
raise NotImplementedError(
f"Forward pass is not implemented when `patch_size` is not None and `norm_type` is '{norm_type}'."
)
elif norm_type == "ada_norm_single" and num_embeds_ada_norm is None:
raise ValueError(
f"When using a `patch_size` and this `norm_type` ({norm_type}), `num_embeds_ada_norm` cannot be None."
)
# Set some common variables used across the board.
self.attention_head_dim = attention_head_dim
self.inner_dim = self.config.num_attention_heads * self.config.attention_head_dim
self.out_channels = in_channels if out_channels is None else out_channels
if use_additional_conditions is None:
if sample_size == 128:
use_additional_conditions = True
else:
use_additional_conditions = False
self.use_additional_conditions = use_additional_conditions
self.gradient_checkpointing = False
# 2. Initialize the position embedding and transformer blocks.
self.height = self.config.sample_size
self.width = self.config.sample_size
interpolation_scale = (
self.config.interpolation_scale
if self.config.interpolation_scale is not None
else max(self.config.sample_size // 64, 1)
)
self.pos_embed = PatchEmbed(
height=self.config.sample_size,
width=self.config.sample_size,
patch_size=self.config.patch_size,
in_channels=self.config.in_channels,
embed_dim=self.inner_dim,
interpolation_scale=interpolation_scale,
)
self.transformer_blocks = nn.ModuleList(
[
BasicTransformerBlock(
self.inner_dim,
self.config.num_attention_heads,
self.config.attention_head_dim,
dropout=self.config.dropout,
cross_attention_dim=self.config.cross_attention_dim,
activation_fn=self.config.activation_fn,
num_embeds_ada_norm=self.config.num_embeds_ada_norm,
attention_bias=self.config.attention_bias,
upcast_attention=self.config.upcast_attention,
norm_type=norm_type,
norm_elementwise_affine=self.config.norm_elementwise_affine,
norm_eps=self.config.norm_eps,
attention_type=self.config.attention_type,
)
for _ in range(self.config.num_layers)
]
)
# 3. Output blocks.
self.norm_out = nn.LayerNorm(self.inner_dim, elementwise_affine=False, eps=1e-6)
self.scale_shift_table = nn.Parameter(torch.randn(2, self.inner_dim) / self.inner_dim**0.5)
self.proj_out = nn.Linear(self.inner_dim, self.config.patch_size * self.config.patch_size * self.out_channels)
self.adaln_single = AdaLayerNormSingle(
self.inner_dim, use_additional_conditions=self.use_additional_conditions
)
self.caption_projection = None
if self.config.caption_channels is not None:
self.caption_projection = PixArtAlphaTextProjection(
in_features=self.config.caption_channels, hidden_size=self.inner_dim
)
def _set_gradient_checkpointing(self, module, value=False):
if hasattr(module, "gradient_checkpointing"):
module.gradient_checkpointing = value
@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
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(FusedAttnProcessor2_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: Optional[torch.Tensor] = None,
timestep: Optional[torch.LongTensor] = None,
added_cond_kwargs: Dict[str, torch.Tensor] = None,
cross_attention_kwargs: Dict[str, Any] = None,
attention_mask: Optional[torch.Tensor] = None,
encoder_attention_mask: Optional[torch.Tensor] = None,
return_dict: bool = True,
):
"""
The [`PixArtTransformer2DModel`] forward method.
Args:
hidden_states (`torch.FloatTensor` of shape `(batch size, channel, height, width)`):
Input `hidden_states`.
encoder_hidden_states (`torch.FloatTensor` of shape `(batch size, sequence len, embed dims)`, *optional*):
Conditional embeddings for cross attention layer. If not given, cross-attention defaults to
self-attention.
timestep (`torch.LongTensor`, *optional*):
Used to indicate denoising step. Optional timestep to be applied as an embedding in `AdaLayerNorm`.
added_cond_kwargs: (`Dict[str, Any]`, *optional*): Additional conditions to be used as inputs.
cross_attention_kwargs ( `Dict[str, Any]`, *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).
attention_mask ( `torch.Tensor`, *optional*):
An attention mask of shape `(batch, key_tokens)` is applied to `encoder_hidden_states`. If `1` the mask
is kept, otherwise if `0` it is discarded. Mask will be converted into a bias, which adds large
negative values to the attention scores corresponding to "discard" tokens.
encoder_attention_mask ( `torch.Tensor`, *optional*):
Cross-attention mask applied to `encoder_hidden_states`. Two formats supported:
* Mask `(batch, sequence_length)` True = keep, False = discard.
* Bias `(batch, 1, sequence_length)` 0 = keep, -10000 = discard.
If `ndim == 2`: will be interpreted as a mask, then converted into a bias consistent with the format
above. This bias will be added to the cross-attention scores.
return_dict (`bool`, *optional*, defaults to `True`):
Whether or not to return a [`~models.unets.unet_2d_condition.UNet2DConditionOutput`] instead of a plain
tuple.
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 self.use_additional_conditions and added_cond_kwargs is None:
raise ValueError("`added_cond_kwargs` cannot be None when using additional conditions for `adaln_single`.")
# ensure attention_mask is a bias, and give it a singleton query_tokens dimension.
# we may have done this conversion already, e.g. if we came here via UNet2DConditionModel#forward.
# we can tell by counting dims; if ndim == 2: it's a mask rather than a bias.
# expects mask of shape:
# [batch, key_tokens]
# adds singleton query_tokens dimension:
# [batch, 1, key_tokens]
# this helps to broadcast it as a bias over attention scores, which will be in one of the following shapes:
# [batch, heads, query_tokens, key_tokens] (e.g. torch sdp attn)
# [batch * heads, query_tokens, key_tokens] (e.g. xformers or classic attn)
if attention_mask is not None and attention_mask.ndim == 2:
# assume that mask is expressed as:
# (1 = keep, 0 = discard)
# convert mask into a bias that can be added to attention scores:
# (keep = +0, discard = -10000.0)
attention_mask = (1 - attention_mask.to(hidden_states.dtype)) * -10000.0
attention_mask = attention_mask.unsqueeze(1)
# convert encoder_attention_mask to a bias the same way we do for attention_mask
if encoder_attention_mask is not None and encoder_attention_mask.ndim == 2:
encoder_attention_mask = (1 - encoder_attention_mask.to(hidden_states.dtype)) * -10000.0
encoder_attention_mask = encoder_attention_mask.unsqueeze(1)
# 1. Input
batch_size = hidden_states.shape[0]
height, width = (
hidden_states.shape[-2] // self.config.patch_size,
hidden_states.shape[-1] // self.config.patch_size,
)
hidden_states = self.pos_embed(hidden_states)
timestep, embedded_timestep = self.adaln_single(
timestep, added_cond_kwargs, batch_size=batch_size, hidden_dtype=hidden_states.dtype
)
if self.caption_projection is not None:
encoder_hidden_states = self.caption_projection(encoder_hidden_states)
encoder_hidden_states = encoder_hidden_states.view(batch_size, -1, hidden_states.shape[-1])
# 2. Blocks
for block in self.transformer_blocks:
if self.training and self.gradient_checkpointing:
def create_custom_forward(module, return_dict=None):
def custom_forward(*inputs):
if return_dict is not None:
return module(*inputs, return_dict=return_dict)
else:
return module(*inputs)
return custom_forward
ckpt_kwargs: Dict[str, Any] = {"use_reentrant": False} if is_torch_version(">=", "1.11.0") else {}
hidden_states = torch.utils.checkpoint.checkpoint(
create_custom_forward(block),
hidden_states,
attention_mask,
encoder_hidden_states,
encoder_attention_mask,
timestep,
cross_attention_kwargs,
None,
**ckpt_kwargs,
)
else:
hidden_states = block(
hidden_states,
attention_mask=attention_mask,
encoder_hidden_states=encoder_hidden_states,
encoder_attention_mask=encoder_attention_mask,
timestep=timestep,
cross_attention_kwargs=cross_attention_kwargs,
class_labels=None,
)
# 3. Output
shift, scale = (
self.scale_shift_table[None] + embedded_timestep[:, None].to(self.scale_shift_table.device)
).chunk(2, dim=1)
hidden_states = self.norm_out(hidden_states)
# Modulation
hidden_states = hidden_states * (1 + scale.to(hidden_states.device)) + shift.to(hidden_states.device)
hidden_states = self.proj_out(hidden_states)
hidden_states = hidden_states.squeeze(1)
# unpatchify
hidden_states = hidden_states.reshape(
shape=(-1, height, width, self.config.patch_size, self.config.patch_size, self.out_channels)
)
hidden_states = torch.einsum("nhwpqc->nchpwq", hidden_states)
output = hidden_states.reshape(
shape=(-1, self.out_channels, height * self.config.patch_size, width * self.config.patch_size)
)
if not return_dict:
return (output,)
return Transformer2DModelOutput(sample=output)