vllm-omni/vllm_omni/diffusion/models/z_image/pipeline_z_image.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

# Copyright 2025 Alibaba Z-Image Team and 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.

import inspect
import json
import os
from collections.abc import Callable, Iterable
from typing import Any

import PIL.Image
import torch
import torch.nn as nn
from diffusers.image_processor import PipelineImageInput, VaeImageProcessor
from diffusers.schedulers import FlowMatchEulerDiscreteScheduler
from diffusers.utils import logging
from diffusers.utils.torch_utils import randn_tensor
from transformers import AutoConfig, AutoModelForCausalLM, AutoTokenizer
from vllm.model_executor.models.utils import AutoWeightsLoader

from vllm_omni.diffusion.data import DiffusionOutput, OmniDiffusionConfig
from vllm_omni.diffusion.distributed.autoencoders.autoencoder_kl import DistributedAutoencoderKL
from vllm_omni.diffusion.distributed.utils import get_local_device
from vllm_omni.diffusion.model_loader.diffusers_loader import DiffusersPipelineLoader
from vllm_omni.diffusion.model_loader.hub_prefetch import prefetch_subfolders
from vllm_omni.diffusion.models.utils import create_transformers_model
from vllm_omni.diffusion.models.z_image.z_image_transformer import (
    ZImageTransformer2DModel,
)
from vllm_omni.diffusion.profiler.diffusion_pipeline_profiler import DiffusionPipelineProfilerMixin
from vllm_omni.diffusion.request import OmniDiffusionRequest
from vllm_omni.model_executor.model_loader.weight_utils import (
    download_weights_from_hf_specific,
)

logger = logging.get_logger(__name__)  # pylint: disable=invalid-name


def get_post_process_func(
    od_config: OmniDiffusionConfig,
):
    model_name = od_config.model
    if os.path.exists(model_name):
        model_path = model_name
    else:
        model_path = download_weights_from_hf_specific(model_name, None, ["*"])
    vae_config_path = os.path.join(model_path, "vae/config.json")
    with open(vae_config_path) as f:
        vae_config = json.load(f)
        vae_scale_factor = 2 ** (len(vae_config["block_out_channels"]) - 1) if "block_out_channels" in vae_config else 8

    image_processor = VaeImageProcessor(vae_scale_factor=vae_scale_factor * 2, do_convert_rgb=True)

    def post_process_func(
        images: torch.Tensor,
    ):
        return image_processor.postprocess(images)

    return post_process_func


# Copied from diffusers.pipelines.flux.pipeline_flux.calculate_shift
def calculate_shift(
    image_seq_len,
    base_seq_len: int = 256,
    max_seq_len: int = 4096,
    base_shift: float = 0.5,
    max_shift: float = 1.15,
):
    m = (max_shift - base_shift) / (max_seq_len - base_seq_len)
    b = base_shift - m * base_seq_len
    mu = image_seq_len * m + b
    return mu


# Copied from diffusers
def retrieve_latents(
    encoder_output: torch.Tensor, generator: torch.Generator | None = None, sample_mode: str = "sample"
):
    if hasattr(encoder_output, "latent_dist") and sample_mode == "sample":
        return encoder_output.latent_dist.sample(generator)
    elif hasattr(encoder_output, "latent_dist") and sample_mode == "argmax":
        return encoder_output.latent_dist.mode()
    elif hasattr(encoder_output, "latents"):
        return encoder_output.latents
    else:
        raise AttributeError("Could not access latents of provided encoder_output")


# Copied from diffusers.pipelines.stable_diffusion.pipeline_stable_diffusion.retrieve_timesteps
def retrieve_timesteps(
    scheduler,
    num_inference_steps: int | None = None,
    device: str | torch.device | None = None,
    timesteps: list[int] | None = None,
    sigmas: list[float] | None = None,
    **kwargs,
) -> tuple[torch.Tensor, int]:
    r"""
    Calls the scheduler's `set_timesteps` method and retrieves timesteps from the scheduler after the call. Handles
    custom timesteps. Any kwargs will be supplied to `scheduler.set_timesteps`.

    Args:
        scheduler (`SchedulerMixin`):
            The scheduler to get timesteps from.
        num_inference_steps (`int`):
            The number of diffusion steps used when generating samples with a pre-trained model. If used, `timesteps`
            must be `None`.
        device (`str` or `torch.device`, *optional*):
            The device to which the timesteps should be moved to. If `None`, the timesteps are not moved.
        timesteps (`list[int]`, *optional*):
            Custom timesteps used to override the timestep spacing strategy of the scheduler. If `timesteps` is passed,
            `num_inference_steps` and `sigmas` must be `None`.
        sigmas (`list[float]`, *optional*):
            Custom sigmas used to override the timestep spacing strategy of the scheduler. If `sigmas` is passed,
            `num_inference_steps` and `timesteps` must be `None`.

    Returns:
        `Tuple[torch.Tensor, int]`: A tuple where the first element is the timestep schedule from the scheduler and the
        second element is the number of inference steps.
    """
    if timesteps is not None and sigmas is not None:
        raise ValueError("Only one of `timesteps` or `sigmas` can be passed. Please choose one to set custom values")
    if timesteps is not None:
        accepts_timesteps = "timesteps" in set(inspect.signature(scheduler.set_timesteps).parameters.keys())
        if not accepts_timesteps:
            raise ValueError(
                f"The current scheduler class {scheduler.__class__}'s `set_timesteps` does not support custom"
                f" timestep schedules. Please check whether you are using the correct scheduler."
            )
        scheduler.set_timesteps(timesteps=timesteps, device=device, **kwargs)
        timesteps = scheduler.timesteps
        num_inference_steps = len(timesteps)
    elif sigmas is not None:
        accept_sigmas = "sigmas" in set(inspect.signature(scheduler.set_timesteps).parameters.keys())
        if not accept_sigmas:
            raise ValueError(
                f"The current scheduler class {scheduler.__class__}'s `set_timesteps` does not support custom"
                f" sigmas schedules. Please check whether you are using the correct scheduler."
            )
        scheduler.set_timesteps(sigmas=sigmas, device=device, **kwargs)
        timesteps = scheduler.timesteps
        num_inference_steps = len(timesteps)
    else:
        scheduler.set_timesteps(num_inference_steps, device=device, **kwargs)
        timesteps = scheduler.timesteps
    return timesteps, num_inference_steps


class ZImagePipeline(nn.Module, DiffusionPipelineProfilerMixin):
    def __init__(
        self,
        *,
        od_config: OmniDiffusionConfig,
        prefix: str = "",
    ):
        super().__init__()
        self.od_config = od_config
        self.weights_sources = [
            DiffusersPipelineLoader.ComponentSource(
                model_or_path=od_config.model,
                subfolder="text_encoder",
                revision=od_config.revision,
                prefix="text_encoder.",
            ),
            DiffusersPipelineLoader.ComponentSource(
                model_or_path=od_config.model,
                subfolder="transformer",
                revision=od_config.revision,
                prefix="transformer.",
                fall_back_to_pt=True,
            ),
            DiffusersPipelineLoader.ComponentSource(
                model_or_path=od_config.model,
                subfolder="vae",
                revision=od_config.revision,
                prefix="vae.",
            ),
        ]
        self._execution_device = get_local_device()
        model = od_config.model
        local_files_only = os.path.exists(model)

        # See ``hub_prefetch.py`` for the transformers v5 subfolder race.
        prefetch_subfolders(
            model,
            ["scheduler", "text_encoder", "vae", "tokenizer"],
            local_files_only=local_files_only,
        )

        self.scheduler = FlowMatchEulerDiscreteScheduler.from_pretrained(
            model, subfolder="scheduler", local_files_only=local_files_only
        )

        text_encoder_config = AutoConfig.from_pretrained(
            model, subfolder="text_encoder", local_files_only=local_files_only
        )
        self.text_encoder = create_transformers_model(
            AutoModelForCausalLM,
            od_config,
            hf_config=text_encoder_config,
        ).to(self._execution_device)
        if text_encoder_config.tie_word_embeddings:
            self.text_encoder.lm_head.weight = self.text_encoder.get_input_embeddings().weight

        vae_config = DistributedAutoencoderKL.load_config(model, subfolder="vae", local_files_only=local_files_only)
        self.vae = DistributedAutoencoderKL.from_config(vae_config).to(self._execution_device)
        self.transformer = ZImageTransformer2DModel(quant_config=od_config.quantization_config)
        self.tokenizer = AutoTokenizer.from_pretrained(model, subfolder="tokenizer", local_files_only=local_files_only)

        # Note: Context parallelism is applied centrally in registry.initialize_model()
        # following diffusers' pattern of enable_parallelism() at model loading time

        self.vae_scale_factor = (
            2 ** (len(self.vae.config.block_out_channels) - 1) if hasattr(self, "vae") and self.vae is not None else 8
        )
        self.setup_diffusion_pipeline_profiler(
            enable_diffusion_pipeline_profiler=self.od_config.enable_diffusion_pipeline_profiler
        )

        self.image_processor = VaeImageProcessor(vae_scale_factor=self.vae_scale_factor * 2, do_convert_rgb=True)

    def encode_prompt(
        self,
        prompt: str | list[str],
        device: torch.device | None = None,
        do_classifier_free_guidance: bool = True,
        negative_prompt: str | list[str] | None = None,
        prompt_embeds: list[torch.FloatTensor] | None = None,
        negative_prompt_embeds: torch.FloatTensor | None = None,
        max_sequence_length: int = 512,
    ):
        prompt = [prompt] if isinstance(prompt, str) else prompt
        prompt_embeds = self._encode_prompt(
            prompt=prompt,
            device=device,
            prompt_embeds=prompt_embeds,
            max_sequence_length=max_sequence_length,
        )

        if do_classifier_free_guidance:
            if negative_prompt is None:
                negative_prompt = ["" for _ in prompt]
            else:
                negative_prompt = [negative_prompt] if isinstance(negative_prompt, str) else negative_prompt
            assert len(prompt) == len(negative_prompt)
            negative_prompt_embeds = self._encode_prompt(
                prompt=negative_prompt,
                device=device,
                prompt_embeds=negative_prompt_embeds,
                max_sequence_length=max_sequence_length,
            )
        else:
            negative_prompt_embeds = []
        return prompt_embeds, negative_prompt_embeds

    def _encode_prompt(
        self,
        prompt: str | list[str],
        device: torch.device | None = None,
        prompt_embeds: list[torch.FloatTensor] | None = None,
        max_sequence_length: int = 512,
    ) -> list[torch.FloatTensor]:
        device = device or self._execution_device

        if prompt_embeds is not None:
            return prompt_embeds

        if isinstance(prompt, str):
            prompt = [prompt]

        for i, prompt_item in enumerate(prompt):
            messages = [
                {"role": "user", "content": prompt_item},
            ]
            prompt_item = self.tokenizer.apply_chat_template(
                messages,
                tokenize=False,
                add_generation_prompt=True,
                enable_thinking=True,
            )
            prompt[i] = prompt_item

        text_inputs = self.tokenizer(
            prompt,
            padding="max_length",
            max_length=max_sequence_length,
            truncation=True,
            return_tensors="pt",
        )

        text_input_ids = text_inputs.input_ids.to(device)
        prompt_masks = text_inputs.attention_mask.to(device).bool()

        prompt_embeds = self.text_encoder(
            input_ids=text_input_ids,
            attention_mask=prompt_masks,
            output_hidden_states=True,
        ).hidden_states[-2]

        embeddings_list = []

        for i in range(len(prompt_embeds)):
            embeddings_list.append(prompt_embeds[i][prompt_masks[i]])

        return embeddings_list

    def prepare_latents(
        self,
        batch_size,
        num_channels_latents,
        height,
        width,
        dtype,
        device,
        generator,
        latents=None,
        image=None,
        timestep=None,
    ):
        height = 2 * (int(height) // (self.vae_scale_factor * 2))
        width = 2 * (int(width) // (self.vae_scale_factor * 2))

        shape = (batch_size, num_channels_latents, height, width)

        if image is not None:
            if latents is not None:
                return latents.to(device=device, dtype=dtype)

            image = image.to(device=device, dtype=dtype)
            if image.shape[1] != num_channels_latents:
                if isinstance(generator, list):
                    image_latents = [
                        retrieve_latents(self.vae.encode(image[i : i + 1]), generator=generator[i])
                        for i in range(image.shape[0])
                    ]
                    image_latents = torch.cat(image_latents, dim=0)
                else:
                    image_latents = retrieve_latents(self.vae.encode(image), generator=generator)

                image_latents = (image_latents - self.vae.config.shift_factor) * self.vae.config.scaling_factor
            else:
                image_latents = image

            if batch_size > image_latents.shape[0] and batch_size % image_latents.shape[0] == 0:
                additional_image_per_prompt = batch_size // image_latents.shape[0]
                image_latents = torch.cat([image_latents] * additional_image_per_prompt, dim=0)
            elif batch_size > image_latents.shape[0] and batch_size % image_latents.shape[0] != 0:
                raise ValueError(
                    f"Cannot duplicate `image` of batch size {image_latents.shape[0]} to {batch_size} text prompts."
                )

            noise = randn_tensor(shape, generator=generator, device=device, dtype=dtype)
            latents = self.scheduler.scale_noise(image_latents, timestep, noise)
            return latents

        if latents is None:
            latents = randn_tensor(shape, generator=generator, device=device, dtype=dtype)
        else:
            if latents.shape != shape:
                raise ValueError(f"Unexpected latents shape, got {latents.shape}, expected {shape}")
            latents = latents.to(device)
        return latents

    def get_timesteps(self, num_inference_steps, strength, device):
        init_timestep = min(num_inference_steps * strength, num_inference_steps)
        t_start = int(max(num_inference_steps - init_timestep, 0))
        timesteps = self.scheduler.timesteps[t_start * self.scheduler.order :]
        if hasattr(self.scheduler, "set_begin_index"):
            self.scheduler.set_begin_index(t_start * self.scheduler.order)
        return timesteps, num_inference_steps - t_start

    @property
    def guidance_scale(self):
        return self._guidance_scale

    @property
    def do_classifier_free_guidance(self):
        return self._guidance_scale > 0

    @property
    def joint_attention_kwargs(self):
        return self._joint_attention_kwargs

    @property
    def num_timesteps(self):
        return self._num_timesteps

    @property
    def interrupt(self):
        return self._interrupt

    def forward(
        self,
        req: OmniDiffusionRequest,
        prompt: str | list[str] | None = None,
        image: PipelineImageInput = None,
        strength: float = 0.6,
        height: int = 1024,
        width: int = 1024,
        num_inference_steps: int = 50,
        sigmas: list[float] | None = None,
        guidance_scale: float = 5.0,
        cfg_normalization: bool = False,
        cfg_truncation: float = 1.0,
        negative_prompt: str | list[str] | None = None,
        num_images_per_prompt: int = 1,
        generator: torch.Generator | list[torch.Generator] | None = None,
        latents: torch.FloatTensor | None = None,
        prompt_embeds: list[torch.FloatTensor] | None = None,
        negative_prompt_embeds: list[torch.FloatTensor] | None = None,
        output_type: str | None = "pil",
        return_dict: bool = True,
        joint_attention_kwargs: dict[str, Any] | None = None,
        callback_on_step_end: Callable[[int, int, dict], None] | None = None,
        callback_on_step_end_tensor_inputs: list[str] = ["latents"],
        max_sequence_length: int = 512,
    ) -> DiffusionOutput:
        r"""
        Function invoked when calling the pipeline for generation.

        Args:
            prompt (`str` or `list[str]`, *optional*):
                The prompt or prompts to guide the image generation. If not defined, one has to pass `prompt_embeds`.
                instead.
            image (`PipelineImageInput`, *optional*):
                The image to use for img2img generation. If provided, the pipeline
                will perform img2img instead of text-to-image.
            strength (`float`, *optional*, defaults to 0.6):
                Indicates extent to transform the reference `image`. Must be between 0 and 1.
            height (`int`, *optional*, defaults to 1024):
                The height in pixels of the generated image.
            width (`int`, *optional*, defaults to 1024):
                The width in pixels of the generated image.
            num_inference_steps (`int`, *optional*, defaults to 50):
                The number of denoising steps. More denoising steps usually lead to a higher quality image at the
                expense of slower inference.
            sigmas (`list[float]`, *optional*):
                Custom sigmas to use for the denoising process with schedulers which support a `sigmas` argument in
                their `set_timesteps` method. If not defined, the default behavior when `num_inference_steps` is passed
                will be used.
            guidance_scale (`float`, *optional*, defaults to 5.0):
                Guidance scale as defined in [Classifier-Free Diffusion Guidance](https://arxiv.org/abs/2207.12598).
                `guidance_scale` is defined as `w` of equation 2. of [Imagen
                Paper](https://arxiv.org/pdf/2205.11487.pdf). Guidance scale is enabled by setting `guidance_scale >
                0`. Higher guidance scale encourages to generate images that are closely linked to the text `prompt`,
                usually at the expense of lower image quality.
            cfg_normalization (`bool`, *optional*, defaults to False):
                Whether to apply configuration normalization.
            cfg_truncation (`float`, *optional*, defaults to 1.0):
                The truncation value for configuration.
            negative_prompt (`str` or `list[str]`, *optional*):
                The prompt or prompts not to guide the image generation. If not defined, one has to pass
                `negative_prompt_embeds` instead. Ignored when not using guidance (i.e., ignored if `guidance_scale` is
                less than or equal to `0`).
            num_images_per_prompt (`int`, *optional*, defaults to 1):
                The number of images to generate per prompt.
            generator (`torch.Generator` or `list[torch.Generator]`, *optional*):
                One or a list of [torch generator(s)](https://pytorch.org/docs/stable/generated/torch.Generator.html)
                to make generation deterministic.
            latents (`torch.FloatTensor`, *optional*):
                Pre-generated noisy latents, sampled from a Gaussian distribution, to be used as inputs for image
                generation. Can be used to tweak the same generation with different prompts. If not provided, a latents
                tensor will be generated by sampling using the supplied random `generator`.
            prompt_embeds (`list[torch.FloatTensor]`, *optional*):
                Pre-generated text embeddings. Can be used to easily tweak text inputs, *e.g.* prompt weighting. If not
                provided, text embeddings will be generated from `prompt` input argument.
            negative_prompt_embeds (`list[torch.FloatTensor]`, *optional*):
                Pre-generated negative text embeddings. Can be used to easily tweak text inputs, *e.g.* prompt
                weighting. If not provided, negative_prompt_embeds will be generated from `negative_prompt` input
                argument.
            output_type (`str`, *optional*, defaults to `"pil"`):
                The output format of the generate image. Choose between
                [PIL](https://pillow.readthedocs.io/en/stable/): `PIL.Image.Image` or `np.array`.
            return_dict (`bool`, *optional*, defaults to `True`):
                Whether or not to return a [`~pipelines.stable_diffusion.ZImagePipelineOutput`] instead of a plain
                tuple.
            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).
            callback_on_step_end (`Callable`, *optional*):
                A function that calls at the end of each denoising steps during the inference. The function is called
                with the following arguments: `callback_on_step_end(self: DiffusionPipeline, step: int, timestep: int,
                callback_kwargs: Dict)`. `callback_kwargs` will include a list of all tensors as specified by
                `callback_on_step_end_tensor_inputs`.
            callback_on_step_end_tensor_inputs (`list`, *optional*):
                The list of tensor inputs for the `callback_on_step_end` function. The tensors specified in the list
                will be passed as `callback_kwargs` argument. You will only be able to include variables listed in the
                `._callback_tensor_inputs` attribute of your pipeline class.
            max_sequence_length (`int`, *optional*, defaults to 512):
                Maximum sequence length to use with the `prompt`.

        Examples:

        Returns:
            [`~pipelines.z_image.ZImagePipelineOutput`] or `tuple`: [`~pipelines.z_image.ZImagePipelineOutput`] if
            `return_dict` is True, otherwise a `tuple`. When returning a tuple, the first element is a list with the
            generated images.
        """
        # TODO: In online mode, sometimes it receives [{"negative_prompt": None}, {...}], so cannot use .get("...", "")
        # TODO: May be some data formatting operations on the API side. Hack for now.
        prompt = [p if isinstance(p, str) else (p.get("prompt") or "") for p in req.prompts] or prompt
        if all(isinstance(p, str) or p.get("negative_prompt") is None for p in req.prompts):
            negative_prompt = None
        elif req.prompts:
            negative_prompt = ["" if isinstance(p, str) else (p.get("negative_prompt") or "") for p in req.prompts]

        # Handle img2img: extract image from request
        if image is None and req.prompts:
            if len(req.prompts) > 1:
                logger.warning(
                    "This model only supports a single prompt for img2img, not a batched request. "
                    "Taking only the first image for now."
                )
            first_prompt = req.prompts[0]
            if not isinstance(first_prompt, str):
                raw_image = first_prompt.get("multi_modal_data", {}).get("image")
                if raw_image is not None:
                    if isinstance(raw_image, list):
                        image = [PIL.Image.open(im) if isinstance(im, str) else raw_image[0] for im in raw_image[:1]]
                    else:
                        image = PIL.Image.open(raw_image) if isinstance(raw_image, str) else raw_image

        # strength is currently only applicable for Z-Image I2I; other pipelines ignore this parameter
        explicit_strength = req.sampling_params.strength is not None
        if explicit_strength:
            strength = req.sampling_params.strength
        if explicit_strength and image is None:
            logger.warning(
                "strength parameter (%.2f) is only applicable for image-to-image (I2I) generation. "
                "It will be ignored for text-to-image (T2I) generation.",
                strength,
            )
            strength = None
        if image is not None and strength is not None and (strength < 0 or strength > 1):
            raise ValueError(f"The value of strength should be in [0.0, 1.0] but is {strength}")

        height = req.sampling_params.height or height
        width = req.sampling_params.width or width
        num_inference_steps = req.sampling_params.num_inference_steps or num_inference_steps
        generator = req.sampling_params.generator
        sigmas = req.sampling_params.sigmas or sigmas
        max_sequence_length = req.sampling_params.max_sequence_length or max_sequence_length
        guidance_scale = (
            req.sampling_params.guidance_scale if req.sampling_params.guidance_rescale is not None else guidance_scale
        )
        num_images_per_prompt = (
            req.sampling_params.num_outputs_per_prompt
            if req.sampling_params.num_outputs_per_prompt > 0
            else num_images_per_prompt
        )

        vae_scale = self.vae_scale_factor * 2
        if height % vae_scale != 0:
            raise ValueError(
                f"Height must be divisible by {vae_scale} (got {height}). "
                f"Please adjust the height to a multiple of {vae_scale}."
            )
        if width % vae_scale != 0:
            raise ValueError(
                f"Width must be divisible by {vae_scale} (got {width}). "
                f"Please adjust the width to a multiple of {vae_scale}."
            )

        device = self._execution_device

        self._guidance_scale = guidance_scale
        self._joint_attention_kwargs = joint_attention_kwargs
        self._interrupt = False
        self._cfg_normalization = cfg_normalization
        self._cfg_truncation = cfg_truncation
        # 2. Define call parameters
        if prompt is not None and isinstance(prompt, str):
            batch_size = 1
        elif prompt is not None and isinstance(prompt, list):
            batch_size = len(prompt)
        else:
            batch_size = len(prompt_embeds)

        # If prompt_embeds is provided and prompt is None, skip encoding
        if prompt_embeds is not None and prompt is None:
            if self.do_classifier_free_guidance and negative_prompt_embeds is None:
                raise ValueError(
                    "When `prompt_embeds` is provided without `prompt`, "
                    "`negative_prompt_embeds` must also be provided for classifier-free guidance."
                )
        else:
            (
                prompt_embeds,
                negative_prompt_embeds,
            ) = self.encode_prompt(
                prompt=prompt,
                negative_prompt=negative_prompt,
                do_classifier_free_guidance=self.do_classifier_free_guidance,
                prompt_embeds=prompt_embeds,
                negative_prompt_embeds=negative_prompt_embeds,
                device=device,
                max_sequence_length=max_sequence_length,
            )

        # 4. Prepare latent variables
        num_channels_latents = self.transformer.in_channels

        # img2img mode: prepare latents from input image
        if image is not None:
            # Handle image list - take first image
            if isinstance(image, list):
                image = image[0]

            # Prepare image for VAE encoding using image_processor
            if not isinstance(image, torch.Tensor):
                init_image = self.image_processor.preprocess(image, height, width)
                image = init_image.to(dtype=torch.float32, device=device)

            # Initialize scheduler kwargs for img2img
            mu = calculate_shift(
                (height // self.vae_scale_factor // 2) * (width // self.vae_scale_factor // 2),
                self.scheduler.config.get("base_image_seq_len", 256),
                self.scheduler.config.get("max_image_seq_len", 4096),
                self.scheduler.config.get("base_shift", 0.5),
                self.scheduler.config.get("max_shift", 1.15),
            )
            self.scheduler.sigma_min = 0.0
            scheduler_kwargs = {"mu": mu}

            # First initialize timesteps in scheduler
            timesteps, num_inference_steps = retrieve_timesteps(
                self.scheduler,
                num_inference_steps,
                device,
                sigmas=sigmas,
                **scheduler_kwargs,
            )

            # Then adjust timesteps based on strength
            timesteps, num_inference_steps = self.get_timesteps(num_inference_steps, strength, device)

            if num_inference_steps < 1:
                raise ValueError(
                    f"After adjusting the num_inference_steps by strength parameter: "
                    f"{strength}, the number of pipeline steps is {num_inference_steps} "
                    f"which is < 1 and not appropriate for this pipeline."
                )
            latent_timestep = timesteps[:1].repeat(batch_size * num_images_per_prompt)

            latents = self.prepare_latents(
                batch_size * num_images_per_prompt,
                num_channels_latents,
                height,
                width,
                prompt_embeds[0].dtype,
                device,
                generator,
                latents,
                image,
                latent_timestep,
            )
        else:
            latents = self.prepare_latents(
                batch_size * num_images_per_prompt,
                num_channels_latents,
                height,
                width,
                torch.float32,
                device,
                generator,
                latents,
            )

        # Repeat prompt_embeds for num_images_per_prompt
        if num_images_per_prompt > 1:
            prompt_embeds = [pe for pe in prompt_embeds for _ in range(num_images_per_prompt)]
            if self.do_classifier_free_guidance and negative_prompt_embeds:
                negative_prompt_embeds = [npe for npe in negative_prompt_embeds for _ in range(num_images_per_prompt)]

        actual_batch_size = batch_size * num_images_per_prompt

        # 5. Prepare timesteps
        if image is None:
            image_seq_len = (latents.shape[2] // 2) * (latents.shape[3] // 2)
            mu = calculate_shift(
                image_seq_len,
                self.scheduler.config.get("base_image_seq_len", 256),
                self.scheduler.config.get("max_image_seq_len", 4096),
                self.scheduler.config.get("base_shift", 0.5),
                self.scheduler.config.get("max_shift", 1.15),
            )
            self.scheduler.sigma_min = 0.0
            scheduler_kwargs = {"mu": mu}

            timesteps, num_inference_steps = retrieve_timesteps(
                self.scheduler,
                num_inference_steps,
                device,
                sigmas=sigmas,
                **scheduler_kwargs,
            )

        num_warmup_steps = max(len(timesteps) - num_inference_steps * self.scheduler.order, 0)
        self._num_timesteps = len(timesteps)

        # Precompute normalized timesteps once to avoid per-step GPU->CPU sync (.item() causes cudaStreamSynchronize)
        if isinstance(timesteps, torch.Tensor):
            timesteps_tensor = timesteps.to(device=device, dtype=torch.float32)
        else:
            timesteps_tensor = torch.as_tensor(timesteps, device=device, dtype=torch.float32)
        norm_timesteps = (1000 - timesteps_tensor) / 1000
        t_norm_list = norm_timesteps.cpu().tolist()
        if not isinstance(t_norm_list, list):
            t_norm_list = [t_norm_list]

        # 6. Denoising loop
        for i, t in enumerate(timesteps):
            if self.interrupt:
                continue

            # broadcast to batch dimension in a way that's compatible with ONNX/Core ML
            timestep = t.expand(latents.shape[0])
            timestep = (1000 - timestep) / 1000
            # Normalized time for time-aware config (0 at start, 1 at end);
            # use precomputed to avoid .item() sync per step
            t_norm = t_norm_list[i]

            # Handle cfg truncation
            current_guidance_scale = self.guidance_scale
            if (
                self.do_classifier_free_guidance
                and self._cfg_truncation is not None
                and float(self._cfg_truncation) <= 1
            ):
                if t_norm > self._cfg_truncation:
                    current_guidance_scale = 0.0

            # Run CFG only if configured AND scale is non-zero
            apply_cfg = self.do_classifier_free_guidance and current_guidance_scale > 0
            latents_typed = latents.to(self.od_config.dtype)

            if apply_cfg:
                latent_model_input = latents_typed.repeat(2, 1, 1, 1)
                prompt_embeds_model_input = prompt_embeds + negative_prompt_embeds
                timestep_model_input = timestep.repeat(2)
            else:
                latent_model_input = latents_typed
                prompt_embeds_model_input = prompt_embeds
                timestep_model_input = timestep

            latent_model_input = latent_model_input.unsqueeze(2)
            latent_model_input_list = list(latent_model_input.unbind(dim=0))

            model_out_list = self.transformer(
                latent_model_input_list,
                timestep_model_input,
                prompt_embeds_model_input,
            )[0]

            if apply_cfg:
                # Perform CFG
                pos_out = model_out_list[:actual_batch_size]
                neg_out = model_out_list[actual_batch_size:]

                noise_pred = []
                for j in range(actual_batch_size):
                    pos = pos_out[j].float()
                    neg = neg_out[j].float()

                    pred = pos + current_guidance_scale * (pos - neg)

                    # Renormalization (torch.where avoids GPU->CPU sync from Python if/scalar comparison)
                    if self._cfg_normalization and float(self._cfg_normalization) > 0.0:
                        ori_pos_norm = torch.linalg.vector_norm(pos)
                        new_pos_norm = torch.linalg.vector_norm(pred)
                        max_new_norm = ori_pos_norm * float(self._cfg_normalization)
                        scale = torch.where(
                            new_pos_norm > max_new_norm,
                            (max_new_norm / new_pos_norm.clamp(min=1e-12)).to(pred.dtype),
                            pred.new_tensor(1.0),
                        )
                        pred = pred * scale

                    noise_pred.append(pred)

                noise_pred = torch.stack(noise_pred, dim=0)
            else:
                noise_pred = torch.stack([t.float() for t in model_out_list], dim=0)

            noise_pred = noise_pred.squeeze(2)
            noise_pred = -noise_pred

            # compute the previous noisy sample x_t -> x_t-1
            latents = self.scheduler.step(noise_pred.to(torch.float32), t, latents, return_dict=False)[0]
            assert latents.dtype == torch.float32

            if callback_on_step_end is not None:
                callback_kwargs = {}
                for k in callback_on_step_end_tensor_inputs:
                    callback_kwargs[k] = locals()[k]
                callback_outputs = callback_on_step_end(self, i, t, callback_kwargs)

                latents = callback_outputs.pop("latents", latents)
                prompt_embeds = callback_outputs.pop("prompt_embeds", prompt_embeds)
                negative_prompt_embeds = callback_outputs.pop("negative_prompt_embeds", negative_prompt_embeds)

        if output_type == "latent":
            image = latents
        else:
            latents = latents.to(self.vae.dtype)
            latents = (latents / self.vae.config.scaling_factor) + self.vae.config.shift_factor

            image = self.vae.decode(latents, return_dict=False)[0]
            # image = self.image_processor.postprocess(image, output_type=output_type)

        return DiffusionOutput(
            output=image, stage_durations=self.stage_durations if hasattr(self, "stage_durations") else None
        )

    def load_weights(self, weights: Iterable[tuple[str, torch.Tensor]]) -> set[str]:
        loader = AutoWeightsLoader(self)
        loaded_weights = loader.load_weights(weights)
        # Record components loaded by diffusers submodules to satisfy strict checks.
        loaded_weights |= {f"vae.{name}" for name, _ in self.vae.named_parameters()}
        # downstream pipelines (e.g. MingImagePipeline) may set ``self.text_encoder = None`` when they
        # bring their own conditioning path.
        if self.text_encoder is not None:
            loaded_weights |= {f"text_encoder.{name}" for name, _ in self.text_encoder.named_parameters()}
        return loaded_weights