It's the guy who made the fancy alignment tool! :D I hope it gets
ported over one day!

In fact, it turns out that Jasper's suggestion of an "interpolation
gradient" was genius! Here's the current setup:

http://postimage.org/image/velcy91a9/

You can add linear, grid or radial interpolation gradients.

The example shown here is a grid gradient. This interpolation
tool can eventually be ported to be applied to just about any
group of objects (but let's just stick to tiling for now...)

Veronika, I didn't see your mail before I finished the
current mock-ups. I do think what you're proposing
could be quite useful for a general interpolation tool. :)
We could start thinking about it separately from the tiling
tool.

Anyway, here's how the interpolation gradient would
work with tiling (grid example):
- Here, you have to define a Row stop and a Column stop.
- By default, applying a grid interpolation gradient will
place the stops on the tiles neighbouring the base tile.
- You can drag that extremity to other tiles.
- You can add Multiple stops! Just like a gradient!

The other tiles aren't updated, this saves some processing
power and avoids some clutter.

Now the handle form is where it gets a bit trickier. I think
the best would be to have a specialized handle of some sort.
Anybody can think of a design?

For blur and opacity, now that we have a few free controllers
(maybe), we could maybe assign Ctrl to Opacity and Shift to
Blur. The user just drags over the frame. Also hold down Alt
to add/remove jitter values.

For HLS interpolation: by default the ghost tile or handle
is without fill, but fill etc. can be added like with any
normal object to launch HLS interpolation. In fact, the user
can switch to the eyedropper tool and take the values of
a target object. Alt-click with the eyedropper to take a
second set of values as jitter reference?

So, the "optimal" work flow is to create sets of two coloured
dots beforehand to set select color interpolation and jitter
values. Of course you can also open up the full editor.

To answer a few questions by Tom:
1. Yes, I've also decided that just Normal and Fuse modes are
enough.

2. I want a separate Radial tiling because it's more intuitive
for angle control. In the case of the render frames, you can
manually set a start and end point, and snap to full circle
(and maybe specify if you want more than 1 circle).

When it's snapped to full circle: when editing the angle of
the base tile, it will automatically take values to make a full
circle. Small stuff like that.

3. The thing about guide points and guide segments is that
others have noted the usefulness of placing them elsewhere
than on the tile sides.

4. Skew will be allowed for P1 and P2. If you drag the handles
in certains ways, they will automatically become upright.

5. The problem with live preview is that these tiles take
potentially a long time to render. :S

Since you're here, I don't suppose you'd have an idea as to the
form of the handle for interpolation gradients, would you? :)