Add the ability to rotate a plane

[dankamongmen]

Add ncplane_rotate(n, rad) rotating an ncplane through rad radians (0 <= rad < 2pi). Figure out exactly what it means to do this with a plane full of character graphics. also: Are we rotating around the center? The origin?

[dankamongmen]

Especially interesting here is that we're dealing with non-square cells, erp!

[dankamongmen]

So the idea of rotating general characters is madness, ain't gonna happen. You can sometimes get a pretty good 180 degree flip, and some characters are even amenable to 90, but in general it's not gonna fly.

We'll have to special-case handling of each character either way. So let's enumerate the ones for which square-symmetry rotation is well defined:

• nul
• space
• full block
• partial blocks

Now what about cell aspect ratio? If we have █ and rotate it 180 degrees, that's still █. Rotated 90 degrees, is that ▄▄, or ▀▀, or ▀, or ▄?

In the tetrimino example, we have e.g. (2 rows, 6 columns):

 ██

██████

an ideal rotation set would yield, i think:

(3 rows, 4 columns)
██
████
██

(2 rows, 6 columns)

██████
██

(3 rows, 4 columns)

 ██

████
██

so each cell is definitely becoming the bottom or upper halves of two cells. so the target plane is

(⌈columns / 2⌉) rows x (⌈rows * 2⌉) columns

if we have

23
67890A

this goes to (clockwise)

67
8923
0A

or (counterclockwise)

0A
2389
67

and finally

0A8967
23

so on clockwise rotations, leftmost becomes topmost, rightmost bottommost, topmost rightmost, and bottommost leftmost.

[dankamongmen]

We're now working for planes which come in as all top half-blocks. Need to do a little work to handle others, but it's there. ;D