Only replace vae when it is the broken SDXL 1.0 version

Author: Lincoln Stein

invokeai/backend/model_management/detect_baked_in_vae.py

@@ -0,0 +1,31 @@
+# Copyright (c) 2024 Lincoln Stein and the InvokeAI Development Team
+"""
+This module exports the function has_baked_in_sdxl_vae().
+It returns True if an SDXL checkpoint model has the original SDXL 1.0 VAE,
+which doesn't work properly in fp16 mode.
+"""
+
+import hashlib
+from pathlib import Path
+
+from safetensors.torch import load_file
+
+SDXL_1_0_VAE_HASH = "bc40b16c3a0fa4625abdfc01c04ffc21bf3cefa6af6c7768ec61eb1f1ac0da51"
+
+
+def has_baked_in_sdxl_vae(checkpoint_path: Path) -> bool:
+    """Return true if the checkpoint contains a custom (non SDXL-1.0) VAE."""
+    hash = _vae_hash(checkpoint_path)
+    return hash != SDXL_1_0_VAE_HASH
+
+
+def _vae_hash(checkpoint_path: Path) -> str:
+    checkpoint = load_file(checkpoint_path, device="cpu")
+    vae_keys = [x for x in checkpoint.keys() if x.startswith("first_stage_model.")]
+    hash = hashlib.new("sha256")
+    for key in vae_keys:
+        value = checkpoint[key]
+        hash.update(bytes(key, "UTF-8"))
+        hash.update(bytes(str(value), "UTF-8"))
+
+    return hash.hexdigest()

invokeai/backend/model_management/models/sdxl.py

@@ -1,11 +1,16 @@
 import json
 import os
 from enum import Enum
+from pathlib import Path
 from typing import Literal, Optional
 
 from omegaconf import OmegaConf
 from pydantic import Field
 
+from invokeai.app.services.config import InvokeAIAppConfig
+from invokeai.backend.model_management.detect_baked_in_vae import has_baked_in_sdxl_vae
+from invokeai.backend.util.logging import InvokeAILogger
+
 from .base import (
     BaseModelType,
     DiffusersModel,
@@ -116,17 +121,20 @@ def convert_if_required(
         # The convert script adapted from the diffusers package uses
         # strings for the base model type. To avoid making too many
         # source code changes, we simply translate here
+        if Path(output_path).exists():
+            return output_path
+
         if isinstance(config, cls.CheckpointConfig):
             from invokeai.backend.model_management.models.stable_diffusion import _convert_ckpt_and_cache
 
             # Hack in VAE-fp16 fix - If model sdxl-vae-fp16-fix is installed,
-            # then we bake it into the converted model.
-            from invokeai.app.services.config import InvokeAIAppConfig
-
-            kwargs = dict()
+            # then we bake it into the converted model unless there is already
+            # a nonstandard VAE installed.
+            kwargs = {}
             app_config = InvokeAIAppConfig.get_config()
             vae_path = app_config.models_path / "sdxl/vae/sdxl-vae-fp16-fix"
-            if vae_path.exists():
+            if vae_path.exists() and not has_baked_in_sdxl_vae(Path(model_path)):
+                InvokeAILogger.get_logger().warning("No baked-in VAE detected. Inserting sdxl-vae-fp16-fix.")
                 kwargs["vae_path"] = vae_path
 
             return _convert_ckpt_and_cache(