Loopy / grid.c: new grid type, 'Hats'.

Browse Source

The big mathematical news this month is that a polygon has been
discovered that will tile the plane but only aperiodically. Penrose
tiles achieve this with two tile types; it's been an open question for
decades whether you could do it with only one tile. Now someone has
announced the discovery of such a thing, so _obviously_ this
mathematically exciting tiling ought to be one of the Loopy grid
options!

The polygon, named a 'hat' by its discoverers, consists of the union
of eight cells of the 'Kites' periodic tiling that Loopy already
implements. So all the vertex coordinates of the whole tiling are
vertices of the Kites grid, which makes handling the coordinates in an
exact manner a lot easier than Penrose tilings.

What's _harder_ than Penrose tilings is that, although this tiling can
be generated by a vaguely similar system of recursive expansion, the
expansion is geometrically distorting, which means you can't easily
figure out which tiles can be discarded early to save CPU. Instead
I've come up with a completely different system for generating a patch
of tiling, by using a hierarchical coordinate system to track a
location within many levels of the expansion process without ever
simulating the process as a whole. I'm really quite pleased with that
technique, and am tempted to try switching the Penrose generator over
to it too - except that we'd have to keep the old generator around to
stop old game ids being invalidated, and also, I think it would be
slightly trickier without an underlying fixed grid and without
overlaps in the tile expansion system.

However, before coming up with that, I got most of the way through
implementing the more obvious system of actually doing the expansions.
The result worked, but was very slow (because I changed approach
rather than try to implement tree-pruning under distortion). But the
code was reusable for two other useful purposes: it generated the
lookup tables needed for the production code, and it also generated a
lot of useful diagrams. So I've committed it anyway as a supporting
program, in a new 'aux' source subdirectory, and in aux/doc is a
writeup of the coordinate system's concepts, with all those diagrams.
(That's the kind of thing I'd normally put in a huge comment at the
top of the file, but doing all those diagrams in ASCII art would be
beyond miserable.)

From a gameplay perspective: the hat polygon has 13 edges, but one of
them has a vertex of the Kites tiling in the middle, and sometimes two
other tile boundaries meet at that vertex. I've chosen to represent
every hat as having degree 14 for Loopy purposes, because if you only
included that extra vertex when it was needed, then people would be
forever having to check whether this was a 13-hat or a 14-hat and it
would be nightmarish to play.

Even so, there's a lot of clicking involved to turn all those fiddly
individual edges on or off. This grid is noticeably nicer to play in
'autofollow' mode, by setting LOOPY_AUTOFOLLOW in the environment to
either 'fixed' or 'adaptive'. I'm tempted to make 'fixed' the default,
except that I think it would confuse players of ordinary square Loopy!

...

This commit is contained in:

Simon Tatham

2023-03-26 20:05:40 +01:00

parent 255744676c

commit 8d6647548f

34 changed files with 11955 additions and 3 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download Patch File Download Diff File Expand all files Collapse all files

1713

aux/hatgen.c Normal file

File diff suppressed because it is too large Load Diff