Yes, the Rosetta group has two basic patterns: simple rotations (restricted
to angles that evenly divide into 360) and rotation plus
reflection - I
didn't see the reflection option in your design, perhaps
I missed it.
It's in the Tiling dialogue mock-up for Radial tiling, and in the description of the work sequence for the "Add tiling type" section. I guess I should make a table with the transformation options, and add the Frieze options while I'm at it.
On the previews: I'm actually trying to keep the guides themselves as uncluttered as possible where extra indicators are concerned. That's because one look at the detailed wikipedia base tiles convinced me that they're more confusing than helpful.
As I said, there already are previews, before you create the guides. I think that they're enough to give users an idea of what's going on. Besides, the shapes themselves usually give a clue as to what the transformation will be (if it's a triangle, you know that it isn't simple translation).
The guides can be transformed like any other object, so you can resize, rotate and flip them like normal objects.
I believe the guide points feature is more useful than giving more indicators on the guides themselves: at the end of the day, when the user is designing a seamless tile, what he needs to know most is how a line going out of the tile will connect to the next tile. What happens to the corner of the base tile isn't as useful.
Here's the description again:
When a guide point is created on one side of a guide, counterparts are automatically created on all other sides of the basic guide. All changes to the original will be reflected onto the new tile. What's more, you can click and drag this guide to create a guide
segment. By snapping a node on a guide point and snapping its handle to
the end of the guide segment, and by repeating the
operation with the
node's counterpart, the user can create smooth
transitions from one tile to the next.
Guide points can be moved along the corners of the guides. When you do so, all its counterpoints are updated dynamically. I guess the current mock-ups aren't clear enough, I'll have to make a few new ones. Look at this program:
http://www.cgl.uwaterloo.ca/~csk/software/penrose/
Unlike this program, the guide points can be moved along the sides of the guide. Like this program, by dragging on some of them, a segment is created that also appears on all the guide points' counterparts. Do you understand the concept now? You can know exactly how a line going out of the tile will go back in.
As for the tiling shadow, the problem is how many tiles will be displayed. Controlling the number of tiles must be done from the tiling dialogue rather than from the tiling guide tool. I guess I could add a "show tiles outline" option to the tiling dialogue.