Function coordinateTransformer

// suppose you have an RGBA image data buffer of `width = 100`, `height = 50`, `channels = 4` <br>
// and you have an array of 6 pixel indexes: `idx0 = [1040, 1044, 1048, 1140, 1144, 1148]` <br>
// and you want to convert these indexes to that of an LA image data buffer of `width = 10`, `height = 10`, `channels = 2`, `x = 5`, `y = 10`
// then:
const
	coords0 = {x: 0, y: 0, width: 100, height: 50, channels: 4},
	coords1 = {x: 5, y: 10, width: 10, height: 10, channels: 2},
	coords0_to_coords1 = coordinateTransformer(coords0, coords1),
	idx0 = [4040, 4044, 4048, 4440, 4444, 4448],
	idx1 = idx0.map(coords0_to_coords1) // [10, 12, 14, 30, 32, 34]
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Derivation

/** the equation for mask_intervals can be easily derived as follows:

• p0 = px of data, y0 = y-coords of pixel in data, x0 = x-coords of pixel in data, w0 = width of data, c0 = channels of data
• p1 = px of mask, y1 = y-coords of pixel in mask, x1 = x-coords of pixel in mask, w1 = width of mask, c1 = channels of mask
• y = y-coords of mask's rect, x = x-coords of mask's rect

declare let [w0, w1, c0, c1]: number[]
let
	p0 = (x0 + y0 * w0) * c0,
	x0 = (p0 / c0) % w0,
	y0 = trunc(p0 / (c0 * w0)),
	p1 = (x1 + y1 * w1) * c1,
	x1 = (p1 / c1) % w1,
	y1 = trunc(p1 / (c1 * w1)),
	x  = x0 - x1,
	y  = y0 - y1

// so, now:
p1 = c1 * (x1 + y1 * w1)
p1 = c1 * ((x0 - x) + (y0 - y) * w1)
p1 = c1 * ((((p0 / c0) % w0) - x) + (((p0 / c0) / w0 | 0) - y) * w1)
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