temp.md

Encoding a tile's data

Every tile is made of 16 cells, which have 4 possible walls (top, bottom, right & left) and may hold items and/or escalators.

That data is encoded using 4 bits (in base 16) for every cell, resulting in a 64-character long string for the whole tile.

When decoding that string, it gets split into 16 blocks of 4 characters each. The first two characters of a block represent the walls schema of the cell, the 3rd one tells us the item, and the 4th one is used for escalators.

First two bits: walls

The first two bits get converted to a 4-digit number in base 3. Every digit of that 4-digit number corresponds to a specific wall. We start from the top and go clockwise: top, right, bottom, left.

nth digit	wall
1	top
2	right
3	bottom
4	left

The value of that digit (0, 1 or 2) corresponds to the state of a wall.

Value	wall state
0	no wall
1	wall
2	orange wall

Here is a base 10 to base 3 cheatsheet. It shows the index of every possible walls schema.

First two bits	Walls schema
00	0000
01	0001
02	0002
03	0010
04	0011
05	0012
06	0020
07	0021
08	0022
09	0100
10	0101
11	0102
12	0110
13	0111
14	0112
15	0120
16	0121
17	0122
18	0200
19	0201
20	0202
21	0210
22	0211
23	0212
24	0220
25	0221
26	0222
27	1000
28	1001
29	1002
30	1010
31	1011
32	1012
33	1020
34	1021
35	1022
36	1100
37	1101
38	1102
39	1110
40	1111
41	1112
42	1120
43	1121
44	1122
45	1200
46	1201
47	1202
48	1210
49	1211
50	1212
51	1220
52	1221
53	1222
54	2000
55	2001
56	2002
57	2010
58	2011
59	2012
60	2020
61	2021
62	2022
63	2100
64	2101
65	2102
66	2110
67	2111
68	2112
69	2120
70	2121
71	2122
72	2200
73	2201
74	2202
75	2210
76	2211
77	2212
78	2220
79	2221
80	2222

Example (from tile 1A)

Tile string:    '31i02700[…]'
First block:    '31i0'
First two bits:  31
=> Schema:       1011

Top wall:        1 (wall)
Right wall:      0 (no wall)
Left wall:       1 (wall)
Bottom wall:     1 (wall)

3rd bit: item

The third bit corresponds to the item that a cell may hold. Some of them are color-specific, others aren't. All of them are listed in the table below.

3rd bit	item	color
0	no item	-
1	gate	green
2	gate	orange
3	gate	purple
4	gate	yellow
5	vortex	green
6	vortex	orange
7	vortex	purple
8	vortex	yellow
9	article	green
a	article	orange
b	article	purple
c	article	yellow
d	exit	green
e	exit	orange
f	exit	purple
g	exit	yellow
h	enter	-
i	time	-
j	crystal	-
k	camera	-

Example (from tile 1A)

Tile string:    '31i02700[…]'
First block:    '31i0'
3rd bit:           i
=> Item:         time

4th bit: escalator

The fourth bit is used for escalators. Since a cell can have both an item and an escalator end, we need a new bit for that. It tells us which cell the escalator has to go to (starting from the current cell).

4th bit	coordinates
0	no escalator
1	{x: 0, y: 0}
2	{x: 0, y: 1}
3	{x: 0, y: 2}
4	{x: 0, y: 3}
5	{x: 1, y: 0}
6	{x: 1, y: 1}
7	{x: 1, y: 2}
8	{x: 1, y: 3}
9	{x: 2, y: 0}
a	{x: 2, y: 1}
b	{x: 2, y: 2}
c	{x: 2, y: 3}
d	{x: 3, y: 0}
e	{x: 3, y: 1}
f	{x: 3, y: 2}
g	{x: 3, y: 3}

Example (from tile 15)

Tile string:    '370a4000[…]'
First block:    '370a'
4th bit:            a
=> Escalator:    {x: 2, y: 1}