Fix to allow use of PerpNegGuider with cfg_function_post hooks (like PAG) (#3618)

.gitignore

@@ -16,3 +16,4 @@ venv/
 !/web/extensions/core/
 /tests-ui/data/object_info.json
 /user/
+comfyui*.log

comfy_extras/nodes_perpneg.py

@@ -61,12 +61,38 @@ class Guider_PerpNeg(comfy.samplers.CFGGuider):
         self.neg_scale = neg_scale
 
     def predict_noise(self, x, timestep, model_options={}, seed=None):
+        # in CFGGuider.predict_noise, we call sampling_function(), which uses cfg_function() to compute pos & neg
+        # but we'd rather do a single batch of sampling pos, neg, and empty, so we call calc_cond_batch([pos,neg,empty]) directly
+        
         positive_cond = self.conds.get("positive", None)
         negative_cond = self.conds.get("negative", None)
         empty_cond = self.conds.get("empty_negative_prompt", None)
 
-        out = comfy.samplers.calc_cond_batch(self.inner_model, [negative_cond, positive_cond, empty_cond], x, timestep, model_options)
-        return perp_neg(x, out[1], out[0], out[2], self.neg_scale, self.cfg)
+        (noise_pred_pos, noise_pred_neg, noise_pred_empty) = \
+            comfy.samplers.calc_cond_batch(self.inner_model, [positive_cond, negative_cond, empty_cond], x, timestep, model_options)
+        cfg_result = perp_neg(x, noise_pred_pos, noise_pred_neg, noise_pred_empty, self.neg_scale, self.cfg)
+
+        # normally this would be done in cfg_function, but we skipped 
+        # that for efficiency: we can compute the noise predictions in
+        # a single call to calc_cond_batch() (rather than two)
+        # so we replicate the hook here
+        for fn in model_options.get("sampler_post_cfg_function", []):
+            args = {
+                "denoised": cfg_result,
+                "cond": positive_cond,
+                "uncond": negative_cond,
+                "model": self.inner_model,
+                "uncond_denoised": noise_pred_neg,
+                "cond_denoised": noise_pred_pos,
+                "sigma": timestep,
+                "model_options": model_options,
+                "input": x,
+                # not in the original call in samplers.py:cfg_function, but made available for future hooks
+                "empty_cond": empty_cond,
+                "empty_cond_denoised": noise_pred_empty,}
+            cfg_result = fn(args)
+
+        return cfg_result
 
 class PerpNegGuider:
     @classmethod