Rewrite res_multistep sampler and implement res_multistep_cfg_pp sampler

comfy/k_diffusion/sampling.py

@@ -8,7 +8,6 @@
 
 from . import utils
 from . import deis
-from . import res
 import comfy.model_patcher
 import comfy.model_sampling
 
@@ -1268,18 +1267,72 @@ def post_cfg_function(args):
     return x
 
 @torch.no_grad()
-def sample_res_multistep(model, x, sigmas, extra_args=None, callback=None, disable=None, s_churn=0., s_tmin=0., s_tmax=float('inf'), s_noise=1., noise_sampler=None):
+def res_multistep(model, x, sigmas, extra_args=None, callback=None, disable=None, s_churn=0., s_tmin=0., s_tmax=float('inf'), s_noise=1., noise_sampler=None, cfg_pp=False):
     extra_args = {} if extra_args is None else extra_args
     seed = extra_args.get("seed", None)
     noise_sampler = default_noise_sampler(x, seed=seed) if noise_sampler is None else noise_sampler
+    s_in = x.new_ones([x.shape[0]])
+    sigma_fn = lambda t: t.neg().exp()
+    t_fn = lambda sigma: sigma.log().neg()
+    phi1_fn = lambda t: torch.expm1(t) / t
+    phi2_fn = lambda t: (phi1_fn(t) - 1.0) / t
+
+    old_denoised = None
+    uncond_denoised = None
+    def post_cfg_function(args):
+        nonlocal uncond_denoised
+        uncond_denoised = args["uncond_denoised"]
+        return args["denoised"]
 
-    x0_func = lambda x, sigma: model(x, sigma, **extra_args)
+    if cfg_pp:
+        model_options = extra_args.get("model_options", {}).copy()
+        extra_args["model_options"] = comfy.model_patcher.set_model_options_post_cfg_function(model_options, post_cfg_function, disable_cfg1_optimization=True)
 
-    solver_cfg = res.SolverConfig()
-    solver_cfg.s_churn = s_churn
-    solver_cfg.s_t_max = s_tmax
-    solver_cfg.s_t_min = s_tmin
-    solver_cfg.s_noise = s_noise
+    for i in trange(len(sigmas) - 1, disable=disable):
+        if s_churn > 0:
+            gamma = min(s_churn / (len(sigmas) - 1), 2**0.5 - 1) if s_tmin <= sigmas[i] <= s_tmax else 0.0
+            sigma_hat = sigmas[i] * (gamma + 1)
+        else:
+            gamma = 0
+            sigma_hat = sigmas[i]
 
-    x = res.differential_equation_solver(x0_func, sigmas, solver_cfg, noise_sampler, callback=callback, disable=disable)(x)
+        if gamma > 0:
+            eps = torch.randn_like(x) * s_noise
+            x = x + eps * (sigma_hat**2 - sigmas[i] ** 2) ** 0.5
+        denoised = model(x, sigma_hat * s_in, **extra_args)
+        if callback is not None:
+            callback({"x": x, "i": i, "sigma": sigmas[i], "sigma_hat": sigma_hat, "denoised": denoised})
+        if sigmas[i + 1] == 0 or old_denoised is None:
+            # Euler method
+            if cfg_pp:
+                d = to_d(x, sigma_hat, uncond_denoised)
+                x = denoised + d * sigmas[i + 1]
+            else:
+                d = to_d(x, sigma_hat, denoised)
+                dt = sigmas[i + 1] - sigma_hat
+                x = x + d * dt
+        else:
+            # Second order multistep method in https://arxiv.org/pdf/2308.02157
+            t, t_next, t_prev = t_fn(sigmas[i]), t_fn(sigmas[i + 1]), t_fn(sigmas[i - 1])
+            h = t_next - t
+            c2 = (t_prev - t) / h
+
+            phi1_val, phi2_val = phi1_fn(-h), phi2_fn(-h)
+            b1 = torch.nan_to_num(phi1_val - 1.0 / c2 * phi2_val, nan=0.0)
+            b2 = torch.nan_to_num(1.0 / c2 * phi2_val, nan=0.0)
+
+            if cfg_pp:
+                x = x + (denoised - uncond_denoised)
+
+            x = (sigma_fn(t_next) / sigma_fn(t)) * x + h * (b1 * denoised + b2 * old_denoised)
+
+        old_denoised = denoised
     return x
+
+@torch.no_grad()
+def sample_res_multistep(model, x, sigmas, extra_args=None, callback=None, disable=None, s_churn=0., s_tmin=0., s_tmax=float('inf'), s_noise=1., noise_sampler=None):
+    return res_multistep(model, x, sigmas, extra_args=extra_args, callback=callback, disable=disable, s_churn=s_churn, s_tmin=s_tmin, s_tmax=s_tmax, s_noise=s_noise, noise_sampler=noise_sampler, cfg_pp=False)
+
+@torch.no_grad()
+def sample_res_multistep_cfg_pp(model, x, sigmas, extra_args=None, callback=None, disable=None, s_churn=0., s_tmin=0., s_tmax=float('inf'), s_noise=1., noise_sampler=None):
+    return res_multistep(model, x, sigmas, extra_args=extra_args, callback=callback, disable=disable, s_churn=s_churn, s_tmin=s_tmin, s_tmax=s_tmax, s_noise=s_noise, noise_sampler=noise_sampler, cfg_pp=True)

comfy/samplers.py

@@ -687,7 +687,7 @@ def max_denoise(self, model_wrap, sigmas):
 KSAMPLER_NAMES = ["euler", "euler_cfg_pp", "euler_ancestral", "euler_ancestral_cfg_pp", "heun", "heunpp2","dpm_2", "dpm_2_ancestral",
                   "lms", "dpm_fast", "dpm_adaptive", "dpmpp_2s_ancestral", "dpmpp_2s_ancestral_cfg_pp", "dpmpp_sde", "dpmpp_sde_gpu",
                   "dpmpp_2m", "dpmpp_2m_cfg_pp", "dpmpp_2m_sde", "dpmpp_2m_sde_gpu", "dpmpp_3m_sde", "dpmpp_3m_sde_gpu", "ddpm", "lcm",
-                  "ipndm", "ipndm_v", "deis", "res_multistep"]
+                  "ipndm", "ipndm_v", "deis", "res_multistep", "res_multistep_cfg_pp"]
 
 class KSAMPLER(Sampler):
     def __init__(self, sampler_function, extra_options={}, inpaint_options={}):