If J3DUltra doesn't import, recommend installing VS C++ Redistributable

README.md

@@ -65,6 +65,6 @@ Then run GCFT with:
 Optionally, if you want J3D model previews to display while running from source, you must also clone and build PyJ3DUltra.  
 A script that automates this process is provided. Simply run the following command:  
 `py -3.12 build_pyj3dultra.py`  
-On Windows, you must first [install vcpkg](https://vcpkg.io/en/getting-started) before running that command.  
+On Windows, you must first [install vcpkg](https://vcpkg.io/en/getting-started) and [Visual Studio](https://visualstudio.microsoft.com/vs/community/) before running that command.  
 
 If the script ran successfully with no errors, then the next time you load a J3D model in GCFT you should see a 3D preview.

gcft_ui/j3d_viewer.py

@@ -9,7 +9,7 @@
 from PySide6.QtWidgets import *
 from PySide6.QtOpenGLWidgets import *
 
-from gcft_paths import ASSETS_PATH
+from gcft_paths import ASSETS_PATH, IS_RUNNING_FROM_SOURCE
 from gcft_ui.nav_camera import Camera
 from gclib.j3d import J3D
 from gclib.bti import BTI
@@ -180,6 +180,15 @@ def get_supported_opengl_version(self) -> tuple[int, int]:
 
   def load_model(self, j3d_model: J3D, reset_camera=False, hidden_material_indexes=None):
     if not J3DULTRA_INSTALLED:
+      error_msg = "Cannot show J3D previews, J3DUltra could not be imported."
+      if IS_RUNNING_FROM_SOURCE:
+        error_msg += "\n\n"
+        error_msg += "Make sure you compiled PyJ3DUltra by running the following command:\n"
+        error_msg += "py build_pyj3dultra.py"
+      elif sys.platform == "win32":
+        error_msg += "\n\n"
+        error_msg += "Make sure you have the Microsoft Visual C++ 2015 Redistributable installed."
+      self.error_showing_preview.emit(error_msg)
       return
 
     if j3d_model.file_type not in ["bmd3", "bdl4", "bmd2"]: