raster.ts

1	/**
2	* Metadata for the rasters `npm run terrain` writes into static/.
3	*
4	* These must match the `render` block of content/geography.json — the generator
5	* reads that file, the browser only ever sees the PNGs, and nothing in between
6	* carries the numbers across. test/raster.test.ts asserts the two agree, because
7	* a silent disagreement here would displace the terrain rather than break it, and
8	* that failure mode has already cost this project once (D-024).
9	*/
10	export const RASTER_WIDTH = 2048
11	export const RASTER_HEIGHT = 1192
12	/**
13	* The working range terrain-height.png is stretched across: black is the floor of
14	* it, white the ceiling. It is deliberately not a round number and not anchored at
15	* zero — it only has to cover the terrain that exists, and the tighter it is the
16	* finer every step in it. Below zero is real: lake and sea floors are cut beneath
17	* the datum, and the old fixed 0..5,000 m encoding clipped them flat.
18	*/
19	export const RASTER_MIN_HEIGHT_M = -560
20	export const RASTER_MAX_HEIGHT_M = 4400
21	export const RASTER_HEIGHT_SPAN_M = RASTER_MAX_HEIGHT_M - RASTER_MIN_HEIGHT_M
22
23	export const COLOR_RASTER = 'terrain-color.png'
24	export const HEIGHT_RASTER = 'terrain-height.png'
25
26	/**
27	* Which surface the rasters describe.
28	*
29	* `canon` is Tower: authored geography, generated by `npm run terrain` from
30	* content/geography.json. `cascadia` is not Tower — it is the Pacific
31	* Northwest at 1:1, laid on the same cylinder because the ground from the Pacific
32	* surf east to the Columbia is 312.8 km and Tower's circumference is 314.2, so the
33	* real coast closes the ring on real terrain. It exists as a ruler, to answer "how
34	* big is this actually", and it carries no Tower geography whatsoever. See D-055.
35	*/
36	export type Surface = 'canon' \| 'cascadia'
37
38	export const isSurface = (v: unknown): v is Surface => v === 'canon' \|\| v === 'cascadia'
39
40	/**
41	* The two rasters for a surface.
42	*
43	* Every surface shares RASTER_WIDTH, RASTER_HEIGHT and the height window above —
44	* that is not a coincidence to be relied on quietly but a requirement, because the
45	* interior view bakes the window into its GLSL as literals and would otherwise
46	* need one shader per surface. test/raster.test.ts holds the generators to it.
47	*/
48	export function rasterSet(surface: Surface): { color: string; height: string } {
49	return surface === 'cascadia'
50	? { color: 'cascadia-color.png', height: 'cascadia-height.png' }
51	: { color: COLOR_RASTER, height: HEIGHT_RASTER }
52	}