raster.ts

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`5a57ebae` 2026-09-07 Pavel Safronov	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	*/
`9a621732` 2026-09-08 Pavel Safronov	19	export const RASTER_MIN_HEIGHT_M = -560
`5a57ebae` 2026-09-07 Pavel Safronov	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'
`1affced2` 2026-09-08 Pavel Safronov	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	}