stable-diffusion-webui/modules/sd_samplers_lcm.py

import torch

from k_diffusion import utils, sampling
from k_diffusion.external import DiscreteEpsDDPMDenoiser
from k_diffusion.sampling import default_noise_sampler, trange

from modules import shared, sd_samplers_cfg_denoiser, sd_samplers_kdiffusion, sd_samplers_common


class LCMCompVisDenoiser(DiscreteEpsDDPMDenoiser):
    def __init__(self, model):
        timesteps = 1000
        original_timesteps = 50     # LCM Original Timesteps (default=50, for current version of LCM)
        self.skip_steps = timesteps // original_timesteps

        alphas_cumprod_valid = torch.zeros((original_timesteps), dtype=torch.float32, device=model.device)
        for x in range(original_timesteps):
            alphas_cumprod_valid[original_timesteps - 1 - x] = model.alphas_cumprod[timesteps - 1 - x * self.skip_steps]

        super().__init__(model, alphas_cumprod_valid, quantize=None)


    def get_sigmas(self, n=None,):
        if n is None:
            return sampling.append_zero(self.sigmas.flip(0))

        start = self.sigma_to_t(self.sigma_max)
        end = self.sigma_to_t(self.sigma_min)

        t = torch.linspace(start, end, n, device=shared.sd_model.device)

        return sampling.append_zero(self.t_to_sigma(t))


    def sigma_to_t(self, sigma, quantize=None):
        log_sigma = sigma.log()
        dists = log_sigma - self.log_sigmas[:, None]
        return dists.abs().argmin(dim=0).view(sigma.shape) * self.skip_steps + (self.skip_steps - 1)


    def t_to_sigma(self, timestep):
        t = torch.clamp(((timestep - (self.skip_steps - 1)) / self.skip_steps).float(), min=0, max=(len(self.sigmas) - 1))
        return super().t_to_sigma(t)


    def get_eps(self, *args, **kwargs):
        return self.inner_model.apply_model(*args, **kwargs)


    def get_scaled_out(self, sigma, output, input):
        sigma_data = 0.5
        scaled_timestep = utils.append_dims(self.sigma_to_t(sigma), output.ndim) * 10.0

        c_skip = sigma_data**2 / (scaled_timestep**2 + sigma_data**2)
        c_out = scaled_timestep / (scaled_timestep**2 + sigma_data**2) ** 0.5

        return c_out * output + c_skip * input


    def forward(self, input, sigma, **kwargs):
        c_out, c_in = [utils.append_dims(x, input.ndim) for x in self.get_scalings(sigma)]
        eps = self.get_eps(input * c_in, self.sigma_to_t(sigma), **kwargs)
        return self.get_scaled_out(sigma, input + eps * c_out, input)


def sample_lcm(model, x, sigmas, extra_args=None, callback=None, disable=None, noise_sampler=None):
    extra_args = {} if extra_args is None else extra_args
    noise_sampler = default_noise_sampler(x) if noise_sampler is None else noise_sampler
    s_in = x.new_ones([x.shape[0]])

    for i in trange(len(sigmas) - 1, disable=disable):
        denoised = model(x, sigmas[i] * s_in, **extra_args)

        if callback is not None:
            callback({'x': x, 'i': i, 'sigma': sigmas[i], 'sigma_hat': sigmas[i], 'denoised': denoised})

        x = denoised
        if sigmas[i + 1] > 0:
            x += sigmas[i + 1] * noise_sampler(sigmas[i], sigmas[i + 1])
    return x


class CFGDenoiserLCM(sd_samplers_cfg_denoiser.CFGDenoiser):
    @property
    def inner_model(self):
        if self.model_wrap is None:
            denoiser = LCMCompVisDenoiser
            self.model_wrap = denoiser(shared.sd_model)

        return self.model_wrap


class LCMSampler(sd_samplers_kdiffusion.KDiffusionSampler):
    def __init__(self, funcname, sd_model, options=None):
        super().__init__(funcname, sd_model, options)
        self.model_wrap_cfg = CFGDenoiserLCM(self)
        self.model_wrap = self.model_wrap_cfg.inner_model


samplers_lcm = [('LCM', sample_lcm, ['k_lcm'], {})]
samplers_data_lcm = [
    sd_samplers_common.SamplerData(label, lambda model, funcname=funcname: LCMSampler(funcname, model), aliases, options)
    for label, funcname, aliases, options in samplers_lcm
]