Add: advanced->model->ModelSamplingDiscrete node.

This allows changing the sampling parameters of the model (eps or vpred)
or set the model to use zsnr.

comfy/model_patcher.py

@@ -11,6 +11,8 @@ def __init__(self, model, load_device, offload_device, size=0, current_device=No
         self.model = model
         self.patches = {}
         self.backup = {}
+        self.object_patches = {}
+        self.object_patches_backup = {}
         self.model_options = {"transformer_options":{}}
         self.model_size()
         self.load_device = load_device
@@ -91,6 +93,9 @@ def set_model_attn2_output_patch(self, patch):
     def set_model_output_block_patch(self, patch):
         self.set_model_patch(patch, "output_block_patch")
 
+    def add_object_patch(self, name, obj):
+        self.object_patches[name] = obj
+
     def model_patches_to(self, device):
         to = self.model_options["transformer_options"]
         if "patches" in to:
@@ -150,6 +155,12 @@ def model_state_dict(self, filter_prefix=None):
         return sd
 
     def patch_model(self, device_to=None):
+        for k in self.object_patches:
+            old = getattr(self.model, k)
+            if k not in self.object_patches_backup:
+                self.object_patches_backup[k] = old
+            setattr(self.model, k, self.object_patches[k])
+
         model_sd = self.model_state_dict()
         for key in self.patches:
             if key not in model_sd:
@@ -290,3 +301,9 @@ def unpatch_model(self, device_to=None):
         if device_to is not None:
             self.model.to(device_to)
             self.current_device = device_to
+
+        keys = list(self.object_patches_backup.keys())
+        for k in keys:
+            setattr(self.model, k, self.object_patches_backup[k])
+
+        self.object_patches_backup = {}

comfy/model_sampling.py

@@ -48,7 +48,9 @@ def _register_schedule(self, given_betas=None, beta_schedule="linear", timesteps
         # self.register_buffer('alphas_cumprod_prev', torch.tensor(alphas_cumprod_prev, dtype=torch.float32))
 
         sigmas = ((1 - alphas_cumprod) / alphas_cumprod) ** 0.5
+        self.set_sigmas(sigmas)
 
+    def set_sigmas(self, sigmas):
         self.register_buffer('sigmas', sigmas)
         self.register_buffer('log_sigmas', sigmas.log())
 

comfy_extras/nodes_model_advanced.py

@@ -0,0 +1,57 @@
+import folder_paths
+import comfy.sd
+import comfy.model_sampling
+
+
+def rescale_zero_terminal_snr_sigmas(sigmas):
+    alphas_cumprod = 1 / ((sigmas * sigmas) + 1)
+    alphas_bar_sqrt = alphas_cumprod.sqrt()
+
+    # Store old values.
+    alphas_bar_sqrt_0 = alphas_bar_sqrt[0].clone()
+    alphas_bar_sqrt_T = alphas_bar_sqrt[-1].clone()
+
+    # Shift so the last timestep is zero.
+    alphas_bar_sqrt -= (alphas_bar_sqrt_T)
+
+    # Scale so the first timestep is back to the old value.
+    alphas_bar_sqrt *= alphas_bar_sqrt_0 / (alphas_bar_sqrt_0 - alphas_bar_sqrt_T)
+
+    # Convert alphas_bar_sqrt to betas
+    alphas_bar = alphas_bar_sqrt**2  # Revert sqrt
+    alphas_bar[-1] = 4.8973451890853435e-08
+    return ((1 - alphas_bar) / alphas_bar) ** 0.5
+
+class ModelSamplingDiscrete:
+    @classmethod
+    def INPUT_TYPES(s):
+        return {"required": { "model": ("MODEL",),
+                              "sampling": (["eps", "v_prediction"],),
+                              "zsnr": ("BOOLEAN", {"default": False}),
+                              }}
+
+    RETURN_TYPES = ("MODEL",)
+    FUNCTION = "patch"
+
+    CATEGORY = "advanced/model"
+
+    def patch(self, model, sampling, zsnr):
+        m = model.clone()
+
+        if sampling == "eps":
+            sampling_type = comfy.model_sampling.EPS
+        elif sampling == "v_prediction":
+            sampling_type = comfy.model_sampling.V_PREDICTION
+
+        class ModelSamplingAdvanced(comfy.model_sampling.ModelSamplingDiscrete, sampling_type):
+            pass
+
+        model_sampling = ModelSamplingAdvanced()
+        if zsnr:
+            model_sampling.set_sigmas(rescale_zero_terminal_snr_sigmas(model_sampling.sigmas))
+        m.add_object_patch("model_sampling", model_sampling)
+        return (m, )
+
+NODE_CLASS_MAPPINGS = {
+    "ModelSamplingDiscrete": ModelSamplingDiscrete,
+}

nodes.py

@@ -1798,6 +1798,7 @@ def init_custom_nodes():
         "nodes_freelunch.py",
         "nodes_custom_sampler.py",
         "nodes_hypertile.py",
+        "nodes_model_advanced.py",
     ]
 
     for node_file in extras_files: