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# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
# --------------------------------------------------------
# References:
# GLIDE: https://github.com/openai/glide-text2im
# MAE: https://github.com/facebookresearch/mae/blob/main/models_mae.py
# --------------------------------------------------------
import math
import torch
import torch.nn as nn
import os
import numpy as np
from timm.models.layers import DropPath
from timm.models.vision_transformer import PatchEmbed, Mlp
from .utils import auto_grad_checkpoint, to_2tuple
from .PixArt_blocks import t2i_modulate, CaptionEmbedder, AttentionKVCompress, MultiHeadCrossAttention, T2IFinalLayer, TimestepEmbedder, LabelEmbedder, FinalLayer
class PixArtBlock(nn.Module):
"""
A PixArt block with adaptive layer norm (adaLN-single) conditioning.
"""
def __init__(self, hidden_size, num_heads, mlp_ratio=4.0, drop_path=0, input_size=None, sampling=None, sr_ratio=1, qk_norm=False, **block_kwargs):
super().__init__()
self.norm1 = nn.LayerNorm(hidden_size, elementwise_affine=False, eps=1e-6)
self.attn = AttentionKVCompress(
hidden_size, num_heads=num_heads, qkv_bias=True, sampling=sampling, sr_ratio=sr_ratio,
qk_norm=qk_norm, **block_kwargs
)
self.cross_attn = MultiHeadCrossAttention(hidden_size, num_heads, **block_kwargs)
self.norm2 = nn.LayerNorm(hidden_size, elementwise_affine=False, eps=1e-6)
# to be compatible with lower version pytorch
approx_gelu = lambda: nn.GELU(approximate="tanh")
self.mlp = Mlp(in_features=hidden_size, hidden_features=int(hidden_size * mlp_ratio), act_layer=approx_gelu, drop=0)
self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
self.scale_shift_table = nn.Parameter(torch.randn(6, hidden_size) / hidden_size ** 0.5)
self.sampling = sampling
self.sr_ratio = sr_ratio
def forward(self, x, y, t, mask=None, **kwargs):
B, N, C = x.shape
shift_msa, scale_msa, gate_msa, shift_mlp, scale_mlp, gate_mlp = (self.scale_shift_table[None] + t.reshape(B, 6, -1)).chunk(6, dim=1)
x = x + self.drop_path(gate_msa * self.attn(t2i_modulate(self.norm1(x), shift_msa, scale_msa)).reshape(B, N, C))
x = x + self.cross_attn(x, y, mask)
x = x + self.drop_path(gate_mlp * self.mlp(t2i_modulate(self.norm2(x), shift_mlp, scale_mlp)))
return x
### Core PixArt Model ###
class PixArt(nn.Module):
"""
Diffusion model with a Transformer backbone.
"""
def __init__(
self,
input_size=32,
patch_size=2,
in_channels=4,
hidden_size=1152,
depth=28,
num_heads=16,
mlp_ratio=4.0,
class_dropout_prob=0.1,
pred_sigma=True,
drop_path: float = 0.,
caption_channels=4096,
pe_interpolation=1.0,
pe_precision=None,
config=None,
model_max_length=120,
qk_norm=False,
kv_compress_config=None,
**kwargs,
):
super().__init__()
self.pred_sigma = pred_sigma
self.in_channels = in_channels
self.out_channels = in_channels * 2 if pred_sigma else in_channels
self.patch_size = patch_size
self.num_heads = num_heads
self.pe_interpolation = pe_interpolation
self.pe_precision = pe_precision
self.depth = depth
self.x_embedder = PatchEmbed(input_size, patch_size, in_channels, hidden_size, bias=True)
self.t_embedder = TimestepEmbedder(hidden_size)
num_patches = self.x_embedder.num_patches
self.base_size = input_size // self.patch_size
# Will use fixed sin-cos embedding:
self.register_buffer("pos_embed", torch.zeros(1, num_patches, hidden_size))
approx_gelu = lambda: nn.GELU(approximate="tanh")
self.t_block = nn.Sequential(
nn.SiLU(),
nn.Linear(hidden_size, 6 * hidden_size, bias=True)
)
self.y_embedder = CaptionEmbedder(
in_channels=caption_channels, hidden_size=hidden_size, uncond_prob=class_dropout_prob,
act_layer=approx_gelu, token_num=model_max_length
)
drop_path = [x.item() for x in torch.linspace(0, drop_path, depth)] # stochastic depth decay rule
self.kv_compress_config = kv_compress_config
if kv_compress_config is None:
self.kv_compress_config = {
'sampling': None,
'scale_factor': 1,
'kv_compress_layer': [],
}
self.blocks = nn.ModuleList([
PixArtBlock(
hidden_size, num_heads, mlp_ratio=mlp_ratio, drop_path=drop_path[i],
input_size=(input_size // patch_size, input_size // patch_size),
sampling=self.kv_compress_config['sampling'],
sr_ratio=int(
self.kv_compress_config['scale_factor']
) if i in self.kv_compress_config['kv_compress_layer'] else 1,
qk_norm=qk_norm,
)
for i in range(depth)
])
self.final_layer = T2IFinalLayer(hidden_size, patch_size, self.out_channels)
def forward_raw(self, x, t, y, mask=None, data_info=None):
"""
Original forward pass of PixArt.
x: (N, C, H, W) tensor of spatial inputs (images or latent representations of images)
t: (N,) tensor of diffusion timesteps
y: (N, 1, 120, C) tensor of class labels
"""
x = x.to(self.dtype)
timestep = t.to(self.dtype)
y = y.to(self.dtype)
pos_embed = self.pos_embed.to(self.dtype)
self.h, self.w = x.shape[-2]//self.patch_size, x.shape[-1]//self.patch_size
x = self.x_embedder(x) + pos_embed # (N, T, D), where T = H * W / patch_size ** 2
t = self.t_embedder(timestep.to(x.dtype)) # (N, D)
t0 = self.t_block(t)
y = self.y_embedder(y, self.training) # (N, 1, L, D)
if mask is not None:
if mask.shape[0] != y.shape[0]:
mask = mask.repeat(y.shape[0] // mask.shape[0], 1)
mask = mask.squeeze(1).squeeze(1)
y = y.squeeze(1).masked_select(mask.unsqueeze(-1) != 0).view(1, -1, x.shape[-1])
y_lens = mask.sum(dim=1).tolist()
else:
y_lens = [y.shape[2]] * y.shape[0]
y = y.squeeze(1).view(1, -1, x.shape[-1])
for block in self.blocks:
x = auto_grad_checkpoint(block, x, y, t0, y_lens) # (N, T, D) #support grad checkpoint
x = self.final_layer(x, t) # (N, T, patch_size ** 2 * out_channels)
x = self.unpatchify(x) # (N, out_channels, H, W)
return x
def forward(self, x, timesteps, context, y=None, **kwargs):
"""
Forward pass that adapts comfy input to original forward function
x: (N, C, H, W) tensor of spatial inputs (images or latent representations of images)
timesteps: (N,) tensor of diffusion timesteps
context: (N, 1, 120, C) conditioning
y: extra conditioning.
"""
## Still accepts the input w/o that dim but returns garbage
if len(context.shape) == 3:
context = context.unsqueeze(1)
## run original forward pass
out = self.forward_raw(
x = x.to(self.dtype),
t = timesteps.to(self.dtype),
y = context.to(self.dtype),
)
## only return EPS
out = out.to(torch.float)
eps, rest = out[:, :self.in_channels], out[:, self.in_channels:]
return eps
def unpatchify(self, x):
"""
x: (N, T, patch_size**2 * C)
imgs: (N, H, W, C)
"""
c = self.out_channels
p = self.x_embedder.patch_size[0]
h = w = int(x.shape[1] ** 0.5)
assert h * w == x.shape[1]
x = x.reshape(shape=(x.shape[0], h, w, p, p, c))
x = torch.einsum('nhwpqc->nchpwq', x)
imgs = x.reshape(shape=(x.shape[0], c, h * p, h * p))
return imgs
def get_2d_sincos_pos_embed(embed_dim, grid_size, cls_token=False, extra_tokens=0, pe_interpolation=1.0, base_size=16):
"""
grid_size: int of the grid height and width
return:
pos_embed: [grid_size*grid_size, embed_dim] or [1+grid_size*grid_size, embed_dim] (w/ or w/o cls_token)
"""
if isinstance(grid_size, int):
grid_size = to_2tuple(grid_size)
grid_h = np.arange(grid_size[0], dtype=np.float32) / (grid_size[0]/base_size) / pe_interpolation
grid_w = np.arange(grid_size[1], dtype=np.float32) / (grid_size[1]/base_size) / pe_interpolation
grid = np.meshgrid(grid_w, grid_h) # here w goes first
grid = np.stack(grid, axis=0)
grid = grid.reshape([2, 1, grid_size[1], grid_size[0]])
pos_embed = get_2d_sincos_pos_embed_from_grid(embed_dim, grid)
if cls_token and extra_tokens > 0:
pos_embed = np.concatenate([np.zeros([extra_tokens, embed_dim]), pos_embed], axis=0)
return pos_embed.astype(np.float32)
def get_2d_sincos_pos_embed_from_grid(embed_dim, grid):
assert embed_dim % 2 == 0
# use half of dimensions to encode grid_h
emb_h = get_1d_sincos_pos_embed_from_grid(embed_dim // 2, grid[0]) # (H*W, D/2)
emb_w = get_1d_sincos_pos_embed_from_grid(embed_dim // 2, grid[1]) # (H*W, D/2)
emb = np.concatenate([emb_h, emb_w], axis=1) # (H*W, D)
return emb
def get_1d_sincos_pos_embed_from_grid(embed_dim, pos):
"""
embed_dim: output dimension for each position
pos: a list of positions to be encoded: size (M,)
out: (M, D)
"""
assert embed_dim % 2 == 0
omega = np.arange(embed_dim // 2, dtype=np.float64)
omega /= embed_dim / 2.
omega = 1. / 10000 ** omega # (D/2,)
pos = pos.reshape(-1) # (M,)
out = np.einsum('m,d->md', pos, omega) # (M, D/2), outer product
emb_sin = np.sin(out) # (M, D/2)
emb_cos = np.cos(out) # (M, D/2)
emb = np.concatenate([emb_sin, emb_cos], axis=1) # (M, D)
return emb
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