I had a lot of fun reading yesterday's comments on the 'Hidden 3DS Max Display Mode' - thanks, everyone! :) Although it's not widely known, the RT button DOES have a function. I had a chat about it with Ton Roosendaal and he wrote the following article:
The "rt" button in Blender is there for developers to allow debugging or to hide testing. This value is by-definition not saved in (or read from) a Blender file, so you have to set it each time when you start Blender.
The name comes from an old convention I introduced in the NeoGeo animation studio long ago. We were saving a lot of files with variations of "temp" in the names, and it was never clear what to do with these. The deal we made was that any file named with "rt" would become a deleteable file, free for anyone to remove if you think it's in the way. I still use this a lot, check for example the file https://www.blender.org/bf/rt.jpg , which just is the debug image-of-the-day I upload while discussing coding issues.
What the name comes from I don't know really... I just happened to type it easily. Maybe it's because it has my initials? :)
Here are the current active "rt" hacks in Blender:
Hold ctrl, you can drag buttons around. Used to be 'UI edit mode'. Still saves file "butsetup" in current directory with button coordinates.
Use alternative OpenGL calls for reveiling UI refreshes like button highlights or pulldown menu updates. Seems to work faster on certain older ATI cards.
- rt==2, rt==3
3d window, Transform Manipulator in rotate mode, shows alternative designs
LSCM unwrap on selecting seams in face mode (ALT+Select) or on CTRL+E "mark seam"
Debug print for each multilayer image loaded when image type is Image Sequence
Note: you can find the RT button in the Anim panel on the Scene Buttons window (F10)