City-Lifeline-Cockpit/.scratch/cockpit-real-data-wayfinding/research/probe-contour.mjs

// 一次性探针：采样白母版的逐行轮廓（左右缘 x），用于拟合自绘 SVG 水滴路径。
// 用法：node probe-contour.mjs <png>
import { readFileSync } from 'node:fs'
import { inflateSync } from 'node:zlib'

function decodePng(path) {
    const buf = readFileSync(path)
    let pos = 8
    const idat = []
    let width = 0, height = 0, bitDepth = 0, colorType = 0, palette = null, trns = null
    while (pos < buf.length) {
        const len = buf.readUInt32BE(pos)
        const type = buf.toString('ascii', pos + 4, pos + 8)
        const data = buf.subarray(pos + 8, pos + 8 + len)
        if (type === 'IHDR') {
            width = data.readUInt32BE(0); height = data.readUInt32BE(4)
            bitDepth = data[8]; colorType = data[9]
        } else if (type === 'PLTE') palette = Buffer.from(data)
        else if (type === 'tRNS') trns = Buffer.from(data)
        else if (type === 'IDAT') idat.push(data)
        else if (type === 'IEND') break
        pos += 12 + len
    }
    const channels = colorType === 6 ? 4 : colorType === 2 ? 3 : 1
    const stride = width * channels
    const raw = inflateSync(Buffer.concat(idat))
    const img = Buffer.alloc(height * stride)
    for (let y = 0; y < height; y++) {
        const filter = raw[y * (stride + 1)]
        const row = raw.subarray(y * (stride + 1) + 1, (y + 1) * stride)
        const prev = y > 0 ? img.subarray((y - 1) * stride, y * stride) : null
        const out = img.subarray(y * stride, (y + 1) * stride)
        for (let x = 0; x < stride; x++) {
            const a = x >= channels ? out[x - channels] : 0
            const b = prev ? prev[x] : 0
            const c = prev && x >= channels ? prev[x - channels] : 0
            let v = row[x]
            if (filter === 1) v += a
            else if (filter === 2) v += b
            else if (filter === 3) v += (a + b) >> 1
            else if (filter === 4) {
                const p = a + b - c
                const pa = Math.abs(p - a), pb = Math.abs(p - b), pc = Math.abs(p - c)
                v += pa <= pb && pa <= pc ? a : pb <= pc ? b : c
            }
            out[x] = v & 0xff
        }
    }
    const alphaAt = (x, y) => {
        if (colorType === 6) return img[y * stride + x * 4 + 3]
        if (colorType === 2) return 255
        const idx = img[y * stride + x]
        if (trns && idx < trns.length) return trns[idx]
        return 255
    }
    return { width, height, alphaAt }
}

const file = process.argv[2] || 'public/cockpit/assets/icons/T_MarkPoint_WhiteFull.png'
const { width, height, alphaAt } = decodePng(file)
const MINX = 67, MAXX = 444, MINY = 19, MAXY = 493
const BW = MAXX - MINX + 1, BH = MAXY - MINY + 1

console.log(`== ${file} 逐行轮廓（bbox 相对坐标，宽 = 左右缘跨度 / bbox 宽）==`)
for (let i = 0; i <= 20; i++) {
    const t = i / 20 // 0=顶 1=底
    const y = Math.round(MINY + t * (MAXY - MINY))
    let lo = -1, hi = -1
    for (let x = MINX; x <= MAXX; x++) {
        if (alphaAt(x, y) > 8) { if (lo < 0) lo = x; hi = x }
    }
    if (lo < 0) { console.log(`t=${t.toFixed(2)} y=${y}  (空)`); continue }
    const lx = ((lo - MINX) / BW).toFixed(3)
    const rx = ((hi - MINX) / BW).toFixed(3)
    const w = ((hi - lo + 1) / BW).toFixed(3)
    console.log(`t=${t.toFixed(2)} y=${y}  左${lx} 右${rx} 宽${w}`)
}

// 圆帽拟合验证：找最宽行与其 y，算帽心/半径（bbox 相对）
let widest = 0, widestY = MINY
for (let y = MINY; y <= MAXY; y++) {
    let lo = -1, hi = -1
    for (let x = MINX; x <= MAXX; x++) if (alphaAt(x, y) > 8) { if (lo < 0) lo = x; hi = x }
    if (lo >= 0 && hi - lo + 1 > widest) { widest = hi - lo + 1; widestY = y }
}
console.log(`\n最宽行 y=${widestY}（相对 ${(widestY - MINY) / BH}）宽 ${widest} = bbox 宽 ${(widest / BW).toFixed(3)}`)