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Python

# SPDX-License-Identifier: Apache-2.0
from __future__ import annotations
from contextlib import nullcontext
from dataclasses import dataclass
import math
from typing import Any
import torch
import torch.nn as nn
from fastvideo.layers.rotary_embedding import apply_rotary_emb, get_1d_rotary_pos_embed
from fastvideo.attention import DistributedAttention
from fastvideo.configs.models import DiTConfig
from fastvideo.forward_context import get_forward_context, set_forward_context
from fastvideo.layers.linear import ReplicatedLinear
from fastvideo.layers.visual_embedding import Timesteps
from fastvideo.models.dits.base import BaseDiT
from fastvideo.models.dits.sd3 import (
CombinedTimestepTextProjEmbeddings,
SD3AdaLayerNormContinuous,
SD3AdaLayerNormZero,
SD3FeedForward,
SD3TextProjection,
SD3TimestepEmbedding,
)
from fastvideo.platforms import AttentionBackendEnum
@dataclass
class FluxTransformer2DModelOutput:
sample: torch.Tensor
class FluxPosEmbed(nn.Module):
"""1D RoPE axes concatenated per Diffusers `FluxPosEmbed`."""
def __init__(self, theta: int, axes_dim: list[int]) -> None:
super().__init__()
self.theta = theta
self.axes_dim = axes_dim
def forward(self, ids: torch.Tensor) -> tuple[torch.Tensor, torch.Tensor]:
n_axes = ids.shape[-1]
cos_out: list[torch.Tensor] = []
sin_out: list[torch.Tensor] = []
pos = ids.float()
is_mps = ids.device.type == "mps"
is_npu = ids.device.type == "npu"
freqs_dtype = torch.float32 if (is_mps or is_npu) else torch.float64
for i in range(n_axes):
cos, sin = get_1d_rotary_pos_embed(
self.axes_dim[i],
pos[:, i],
theta=self.theta,
use_real=True,
freqs_dtype=freqs_dtype,
)
cos_out.append(cos)
sin_out.append(sin)
freqs_cos = torch.cat(cos_out, dim=-1).to(ids.device)
freqs_sin = torch.cat(sin_out, dim=-1).to(ids.device)
return freqs_cos, freqs_sin
class FluxCombinedTimestepGuidanceTextProjEmbeddings(nn.Module):
def __init__(self, embedding_dim: int, pooled_projection_dim: int) -> None:
super().__init__()
self.time_proj = Timesteps(
num_channels=256,
flip_sin_to_cos=True,
downscale_freq_shift=0,
)
self.timestep_embedder = SD3TimestepEmbedding(
in_channels=256,
time_embed_dim=embedding_dim,
act_fn="silu",
)
self.guidance_embedder = SD3TimestepEmbedding(
in_channels=256,
time_embed_dim=embedding_dim,
act_fn="silu",
)
self.text_embedder = SD3TextProjection(
pooled_projection_dim,
embedding_dim,
act_fn="silu",
)
def forward(
self,
timestep: torch.Tensor,
guidance: torch.Tensor,
pooled_projection: torch.Tensor,
) -> torch.Tensor:
timesteps_proj = self.time_proj(timestep)
timesteps_emb = self.timestep_embedder(timesteps_proj.to(dtype=pooled_projection.dtype))
guidance_proj = self.time_proj(guidance)
guidance_emb = self.guidance_embedder(guidance_proj.to(dtype=pooled_projection.dtype))
time_guidance_emb = timesteps_emb + guidance_emb
pooled_projections = self.text_embedder(pooled_projection)
return time_guidance_emb + pooled_projections
class FluxAdaLayerNormZeroSingle(nn.Module):
def __init__(self, embedding_dim: int, bias: bool = True) -> None:
super().__init__()
self.silu = nn.SiLU()
self.linear = ReplicatedLinear(embedding_dim, 3 * embedding_dim, bias=bias)
self.norm = nn.LayerNorm(embedding_dim, elementwise_affine=False, eps=1e-6)
def forward(
self,
x: torch.Tensor,
emb: torch.Tensor,
) -> tuple[torch.Tensor, torch.Tensor]:
emb, _ = self.linear(self.silu(emb))
shift_msa, scale_msa, gate_msa = emb.chunk(3, dim=1)
x = self.norm(x) * (1 + scale_msa[:, None]) + shift_msa[:, None]
return x, gate_msa
class FluxJointAttention(nn.Module):
"""Joint attention: text tokens precede image tokens (Diffusers order)."""
def __init__(
self,
dim: int,
num_attention_heads: int,
attention_head_dim: int,
supported_attention_backends: tuple[AttentionBackendEnum, ...] | None = None,
) -> None:
super().__init__()
self.heads = num_attention_heads
self.head_dim = attention_head_dim
self.inner_dim = num_attention_heads * attention_head_dim
self.norm_q = nn.RMSNorm(attention_head_dim, eps=1e-6)
self.norm_k = nn.RMSNorm(attention_head_dim, eps=1e-6)
self.norm_added_q = nn.RMSNorm(attention_head_dim, eps=1e-6)
self.norm_added_k = nn.RMSNorm(attention_head_dim, eps=1e-6)
self.to_q = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.to_k = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.to_v = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.add_q_proj = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.add_k_proj = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.add_v_proj = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.to_out = nn.ModuleList([
ReplicatedLinear(self.inner_dim, dim, bias=True),
nn.Dropout(0.0),
])
self.to_add_out = ReplicatedLinear(self.inner_dim, dim, bias=True)
self.attn = DistributedAttention(
num_heads=num_attention_heads,
head_size=attention_head_dim,
causal=False,
supported_attention_backends=supported_attention_backends,
)
def forward(
self,
hidden_states: torch.Tensor,
encoder_hidden_states: torch.Tensor,
image_rotary_emb: tuple[torch.Tensor, torch.Tensor],
) -> tuple[torch.Tensor, torch.Tensor]:
batch_size = hidden_states.shape[0]
text_seq_len = encoder_hidden_states.shape[1]
img_seq_len = hidden_states.shape[1]
q, _ = self.to_q(hidden_states)
k, _ = self.to_k(hidden_states)
v, _ = self.to_v(hidden_states)
q = q.view(batch_size, img_seq_len, self.heads, self.head_dim)
k = k.view(batch_size, img_seq_len, self.heads, self.head_dim)
v = v.view(batch_size, img_seq_len, self.heads, self.head_dim)
q = self.norm_q(q)
k = self.norm_k(k)
enc_q, _ = self.add_q_proj(encoder_hidden_states)
enc_k, _ = self.add_k_proj(encoder_hidden_states)
enc_v, _ = self.add_v_proj(encoder_hidden_states)
enc_q = enc_q.view(batch_size, text_seq_len, self.heads, self.head_dim)
enc_k = enc_k.view(batch_size, text_seq_len, self.heads, self.head_dim)
enc_v = enc_v.view(batch_size, text_seq_len, self.heads, self.head_dim)
enc_q = self.norm_added_q(enc_q)
enc_k = self.norm_added_k(enc_k)
q = torch.cat([enc_q, q], dim=1)
k = torch.cat([enc_k, k], dim=1)
v = torch.cat([enc_v, v], dim=1)
q = apply_rotary_emb(q, image_rotary_emb, sequence_dim=1)
k = apply_rotary_emb(k, image_rotary_emb, sequence_dim=1)
joint_out, _ = self.attn(q, k, v)
joint_out = joint_out.reshape(batch_size, text_seq_len + img_seq_len, self.inner_dim)
enc_out = joint_out[:, :text_seq_len]
img_out = joint_out[:, text_seq_len:]
img_out, _ = self.to_out[0](img_out)
img_out = self.to_out[1](img_out)
enc_out, _ = self.to_add_out(enc_out)
return img_out, enc_out
class FluxSingleStreamAttention(nn.Module):
"""Self-attention on concatenated text+image sequence (single blocks)."""
def __init__(
self,
dim: int,
num_attention_heads: int,
attention_head_dim: int,
supported_attention_backends: tuple[AttentionBackendEnum, ...] | None = None,
) -> None:
super().__init__()
self.heads = num_attention_heads
self.head_dim = attention_head_dim
self.inner_dim = num_attention_heads * attention_head_dim
self.norm_q = nn.RMSNorm(attention_head_dim, eps=1e-6)
self.norm_k = nn.RMSNorm(attention_head_dim, eps=1e-6)
self.to_q = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.to_k = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.to_v = ReplicatedLinear(dim, self.inner_dim, bias=True)
self.attn = DistributedAttention(
num_heads=num_attention_heads,
head_size=attention_head_dim,
causal=False,
supported_attention_backends=supported_attention_backends,
)
def forward(
self,
hidden_states: torch.Tensor,
image_rotary_emb: tuple[torch.Tensor, torch.Tensor],
) -> torch.Tensor:
batch_size, seq_len, _ = hidden_states.shape
q, _ = self.to_q(hidden_states)
k, _ = self.to_k(hidden_states)
v, _ = self.to_v(hidden_states)
q = q.view(batch_size, seq_len, self.heads, self.head_dim)
k = k.view(batch_size, seq_len, self.heads, self.head_dim)
v = v.view(batch_size, seq_len, self.heads, self.head_dim)
q = self.norm_q(q)
k = self.norm_k(k)
q = apply_rotary_emb(q, image_rotary_emb, sequence_dim=1)
k = apply_rotary_emb(k, image_rotary_emb, sequence_dim=1)
out, _ = self.attn(q, k, v)
return out.reshape(batch_size, seq_len, self.inner_dim)
class FluxTransformerBlock(nn.Module):
def __init__(
self,
dim: int,
num_attention_heads: int,
attention_head_dim: int,
supported_attention_backends: tuple[AttentionBackendEnum, ...] | None = None,
) -> None:
super().__init__()
self.norm1 = SD3AdaLayerNormZero(dim)
self.norm1_context = SD3AdaLayerNormZero(dim)
self.attn = FluxJointAttention(
dim=dim,
num_attention_heads=num_attention_heads,
attention_head_dim=attention_head_dim,
supported_attention_backends=supported_attention_backends,
)
self.norm2 = nn.LayerNorm(dim, elementwise_affine=False, eps=1e-6)
self.ff = SD3FeedForward(
dim=dim,
dim_out=dim,
activation_fn="gelu-approximate",
)
self.norm2_context = nn.LayerNorm(dim, elementwise_affine=False, eps=1e-6)
self.ff_context = SD3FeedForward(
dim=dim,
dim_out=dim,
activation_fn="gelu-approximate",
)
def forward(
self,
hidden_states: torch.Tensor,
encoder_hidden_states: torch.Tensor,
temb: torch.Tensor,
image_rotary_emb: tuple[torch.Tensor, torch.Tensor],
joint_attention_kwargs: dict[str, Any] | None = None,
) -> tuple[torch.Tensor, torch.Tensor]:
del joint_attention_kwargs
norm_hidden_states, gate_msa, shift_mlp, scale_mlp, gate_mlp = self.norm1(hidden_states, emb=temb)
(norm_encoder_hidden_states, c_gate_msa, c_shift_mlp, c_scale_mlp,
c_gate_mlp) = self.norm1_context(encoder_hidden_states, emb=temb)
attn_output, context_attn_output = self.attn(
hidden_states=norm_hidden_states,
encoder_hidden_states=norm_encoder_hidden_states,
image_rotary_emb=image_rotary_emb,
)
attn_output = gate_msa.unsqueeze(1) * attn_output
hidden_states = hidden_states + attn_output
norm_hidden_states = self.norm2(hidden_states)
norm_hidden_states = norm_hidden_states * (1 + scale_mlp[:, None]) + shift_mlp[:, None]
ff_output = self.ff(norm_hidden_states)
hidden_states = hidden_states + gate_mlp.unsqueeze(1) * ff_output
context_attn_output = c_gate_msa.unsqueeze(1) * context_attn_output
encoder_hidden_states = encoder_hidden_states + context_attn_output
norm_encoder_hidden_states = self.norm2_context(encoder_hidden_states)
norm_encoder_hidden_states = norm_encoder_hidden_states * (1 + c_scale_mlp[:, None]) + c_shift_mlp[:, None]
context_ff_output = self.ff_context(norm_encoder_hidden_states)
encoder_hidden_states = encoder_hidden_states + (c_gate_mlp.unsqueeze(1) * context_ff_output)
if encoder_hidden_states.dtype == torch.float16:
encoder_hidden_states = encoder_hidden_states.clip(-65504, 65504)
return encoder_hidden_states, hidden_states
class FluxSingleTransformerBlock(nn.Module):
def __init__(
self,
dim: int,
num_attention_heads: int,
attention_head_dim: int,
mlp_ratio: float = 4.0,
supported_attention_backends: tuple[AttentionBackendEnum, ...] | None = None,
) -> None:
super().__init__()
mlp_hidden_dim = int(dim * mlp_ratio)
self.norm = FluxAdaLayerNormZeroSingle(dim)
self.proj_mlp = ReplicatedLinear(dim, mlp_hidden_dim, bias=True)
self.act_mlp = nn.GELU(approximate="tanh")
self.proj_out = ReplicatedLinear(dim + mlp_hidden_dim, dim, bias=True)
self.attn = FluxSingleStreamAttention(
dim=dim,
num_attention_heads=num_attention_heads,
attention_head_dim=attention_head_dim,
supported_attention_backends=supported_attention_backends,
)
def forward(
self,
hidden_states: torch.Tensor,
encoder_hidden_states: torch.Tensor,
temb: torch.Tensor,
image_rotary_emb: tuple[torch.Tensor, torch.Tensor],
joint_attention_kwargs: dict[str, Any] | None = None,
) -> tuple[torch.Tensor, torch.Tensor]:
del joint_attention_kwargs
text_seq_len = encoder_hidden_states.shape[1]
hidden_states = torch.cat([encoder_hidden_states, hidden_states], dim=1)
residual = hidden_states
norm_hidden_states, gate = self.norm(hidden_states, emb=temb)
mlp_hidden_states = self.act_mlp(self.proj_mlp(norm_hidden_states)[0])
attn_output = self.attn(
hidden_states=norm_hidden_states,
image_rotary_emb=image_rotary_emb,
)
hidden_states = torch.cat([attn_output, mlp_hidden_states], dim=2)
gate = gate.unsqueeze(1)
hidden_states = gate * self.proj_out(hidden_states)[0]
hidden_states = residual + hidden_states
if hidden_states.dtype == torch.float16:
hidden_states = hidden_states.clip(-65504, 65504)
encoder_hidden_states = hidden_states[:, :text_seq_len]
hidden_states = hidden_states[:, text_seq_len:]
return encoder_hidden_states, hidden_states
class FluxTransformer2DModel(BaseDiT):
"""FastVideo FLUX transformer; load Diffusers FLUX safetensors 1:1."""
_fsdp_shard_conditions = [
lambda n, m: (n.startswith("transformer_blocks.") or n.startswith("single_transformer_blocks.")) and n.split(
".")[-1].isdigit(),
]
_compile_conditions = _fsdp_shard_conditions
# HF weight names already match this module layout (cf. SGLang regex maps).
param_names_mapping: dict[str, Any] = {}
reverse_param_names_mapping: dict[str, Any] = {}
lora_param_names_mapping: dict[str, Any] = {}
_supported_attention_backends = (
AttentionBackendEnum.FLASH_ATTN,
AttentionBackendEnum.TORCH_SDPA,
)
def __init__(self, config: DiTConfig, hf_config: dict[str, Any], **kwargs) -> None:
del kwargs
super().__init__(config=config, hf_config=hf_config)
self.fastvideo_config = config
self.hf_config = hf_config
arch = config.arch_config
out_ch = arch.out_channels
self.out_channels = out_ch if out_ch is not None else arch.in_channels
self.inner_dim = arch.num_attention_heads * arch.attention_head_dim
self.hidden_size = self.inner_dim
self.num_attention_heads = arch.num_attention_heads
self.num_channels_latents = arch.in_channels
axes_list = list(arch.axes_dims_rope)
self.pos_embed = FluxPosEmbed(theta=10000, axes_dim=axes_list)
if arch.guidance_embeds:
self.time_text_embed = FluxCombinedTimestepGuidanceTextProjEmbeddings(
embedding_dim=self.inner_dim,
pooled_projection_dim=arch.pooled_projection_dim,
)
else:
self.time_text_embed = CombinedTimestepTextProjEmbeddings(
embedding_dim=self.inner_dim,
pooled_projection_dim=arch.pooled_projection_dim,
)
self.context_embedder = ReplicatedLinear(arch.joint_attention_dim, self.inner_dim)
self.x_embedder = ReplicatedLinear(arch.in_channels, self.inner_dim)
self.transformer_blocks = nn.ModuleList([
FluxTransformerBlock(
dim=self.inner_dim,
num_attention_heads=arch.num_attention_heads,
attention_head_dim=arch.attention_head_dim,
supported_attention_backends=self._supported_attention_backends,
) for _ in range(arch.num_layers)
])
self.single_transformer_blocks = nn.ModuleList([
FluxSingleTransformerBlock(
dim=self.inner_dim,
num_attention_heads=arch.num_attention_heads,
attention_head_dim=arch.attention_head_dim,
supported_attention_backends=self._supported_attention_backends,
) for _ in range(arch.num_single_layers)
])
self.norm_out = SD3AdaLayerNormContinuous(
self.inner_dim,
self.inner_dim,
elementwise_affine=False,
eps=1e-6,
bias=True,
norm_type="layer_norm",
)
self.proj_out = ReplicatedLinear(
self.inner_dim,
arch.patch_size * arch.patch_size * self.out_channels,
bias=True,
)
self.gradient_checkpointing = False
self.__post_init__()
def forward(
self,
hidden_states: torch.Tensor,
encoder_hidden_states: torch.Tensor | None = None,
pooled_projections: torch.Tensor | None = None,
timestep: torch.LongTensor | torch.Tensor | None = None,
img_ids: torch.Tensor | None = None,
txt_ids: torch.Tensor | None = None,
guidance: torch.Tensor | None = None,
joint_attention_kwargs: dict[str, Any] | None = None,
return_dict: bool = True,
controlnet_block_samples: Any | None = None,
controlnet_single_block_samples: Any | None = None,
controlnet_blocks_repeat: bool = False,
**kwargs: Any,
) -> FluxTransformer2DModelOutput | tuple[torch.Tensor, ...]:
del kwargs
if encoder_hidden_states is None:
raise ValueError("encoder_hidden_states must be provided")
if pooled_projections is None:
raise ValueError("pooled_projections must be provided")
if timestep is None:
raise ValueError("timestep must be provided")
if img_ids is None or txt_ids is None:
raise ValueError("img_ids and txt_ids must be provided")
arch = self.fastvideo_config.arch_config
if arch.guidance_embeds and guidance is None:
raise ValueError("guidance must be provided when guidance_embeds=True")
if timestep.dim() == 0:
timestep = timestep[None]
if timestep.dim() > 1:
timestep = timestep.reshape(-1)
if timestep.shape[0] == 1 and hidden_states.shape[0] > 1:
timestep = timestep.expand(hidden_states.shape[0])
try:
get_forward_context()
forward_context = nullcontext()
except AssertionError:
if timestep.numel() == 0:
ts0 = 0
elif torch.is_floating_point(timestep):
ts0 = int(round(timestep[0].item() * 1000))
else:
ts0 = int(timestep[0].item())
forward_context = set_forward_context(current_timestep=ts0, attn_metadata=None)
with forward_context:
hidden_states, _ = self.x_embedder(hidden_states)
ts = timestep.to(hidden_states.dtype) * 1000
g = None if guidance is None else guidance.to(hidden_states.dtype) * 1000
if arch.guidance_embeds:
assert g is not None
temb = self.time_text_embed(ts, g, pooled_projections)
else:
temb = self.time_text_embed(timestep=ts, pooled_projection=pooled_projections)
encoder_hidden_states, _ = self.context_embedder(encoder_hidden_states)
if txt_ids.ndim == 3:
txt_ids = txt_ids[0]
if img_ids.ndim == 3:
img_ids = img_ids[0]
ids = torch.cat((txt_ids, img_ids), dim=0)
image_rotary_emb = self.pos_embed(ids)
jkwargs = joint_attention_kwargs or {}
for idx, block in enumerate(self.transformer_blocks):
encoder_hidden_states, hidden_states = block(
hidden_states=hidden_states,
encoder_hidden_states=encoder_hidden_states,
temb=temb,
image_rotary_emb=image_rotary_emb,
joint_attention_kwargs=jkwargs,
)
if controlnet_block_samples:
interval = len(self.transformer_blocks) / len(controlnet_block_samples)
interval = int(math.ceil(interval))
if controlnet_blocks_repeat:
hidden_states = hidden_states + controlnet_block_samples[idx % len(controlnet_block_samples)]
else:
hidden_states = hidden_states + controlnet_block_samples[idx // interval]
for idx, block in enumerate(self.single_transformer_blocks):
encoder_hidden_states, hidden_states = block(
hidden_states=hidden_states,
encoder_hidden_states=encoder_hidden_states,
temb=temb,
image_rotary_emb=image_rotary_emb,
joint_attention_kwargs=jkwargs,
)
if controlnet_single_block_samples:
interval = len(self.single_transformer_blocks) / len(controlnet_single_block_samples)
interval = int(math.ceil(interval))
hidden_states = hidden_states + controlnet_single_block_samples[idx // interval]
hidden_states = self.norm_out(hidden_states, temb)
output, _ = self.proj_out(hidden_states)
if not return_dict:
return (output, )
return FluxTransformer2DModelOutput(sample=output)
EntryClass = FluxTransformer2DModel