Tale of a bad venture :
Hi ! I have lost two days of work because of an error I did using Shrinkwrap Modifiers, and before I understood what was the matter, I had to redo many things from scratch !
I wanted to tell you this venture, because an apparently simple error can have heavy consequences and leads to a blend file that seems to work perfectly well but can’t be opened once saved !
I was building a setup with several mesh objects using Shrinkwrap modifiers to match the surface of the terrain, in the desert scene I’m working on for a while. If you know my “Tracks Creator” creating an animated texture to be used in a second pass for displacement mapping, the last method I’m working on allows to generate detailed and realistic tires tracks in relief in only one pass, directly visible in the 3D viewport.
For that, I used several objects with shrinkwrap modifiers applied in cascade. By error, the last object of the chain pointed to the first one. So it made a loop.
When using constraints, loops are not a problem, and sometimes they can even be an advantage, allowing very interesting things like the self tracking constraint that I use for the rear wheels of cars and trucks in my cars setups.
So I have not suspected this at first glance, and before I found out what happened, I came with a serie of unusable blend files ! When working, I save often my work, but as the problem occurs only once the file is closed, all saved files have been corrupted.
Once closed, the blend file containing a Modifier loop can’t be opened. If you look at the ressources usage in Windows task manager, you will see that memory amount used increases up to the level where the whole memory (8GB in my case) is used and the computer becomes unresponsive and has to be hard-rebooted !
Before, when (rarely) I encountered a file refusing to open, I had created a new file and imported the whole content of the locked file or opened the last working file and imported the recently added objects of the locked file, and this solved the problem.
With Modifiers, before I understood the nature of the trouble, I tried to import the last added objects (included in a group), but as soon I imported the litigious objects, the computer entered in a loop !
It happens as well with Blender 2.49b and 2.55.
So, be careful when working with Modifiers ! I haven’t searched if some other Modifiers may give such surprise, but the Shrinkwrap Modifier must be used with caution ! This said, it is a marvelous tool allowing many interesting effects !
Happy Blending !
