feat: 完善日月食与月掩几何链路并扩展历法接口
- 新增日月食中心带、偏食带、阴影足迹、等时线、食分线及升落边界计算，支持极区与混合食拓扑 - 新增日食单时刻阴影求解器、站心状态查询、批量采样和 ΔT 覆盖接口 - 重构恒星与行星月掩路径，补充有限盘面接触、站心修正、掩带宽度、极区投影及升落边界 - 扩展 SVG 与 GeoJSON 输出，支持详细面板、全球/极区/地球投影、边界闭合、时间标记和拓扑签名 - 扩展日月食候选搜索、局地搜索、沙罗序列预计算与范围外推，补充系列锚点和成员一致性校验 - 补齐古历纪年、儒略历独有闰日、多公历候选、历法改革跨日及精确日期运算接口 - 优化 ΔT、章动、恒星时、月球地平线、事件根搜索和本地星历缓存，降低重复计算开销并提升边界稳定
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package svg
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import (
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"strconv"
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"strings"
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"b612.me/astro/internal/geodata"
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"b612.me/astro/moon"
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)
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// occultationScreenPoint 是投影到 SVG 画布后的像素坐标。
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type occultationScreenPoint struct {
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x float64
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y float64
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}
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// occultationGeometryTolerancePixels 是掩带几何写出前的折线简化容差（像素）；0 表示不简化。
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var occultationGeometryTolerancePixels = 0.4
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// projectOccultationRing 投影并简化一个地理环。
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func (layout starOccultationSVGLayout) projectOccultationRing(points []starOccultationGeoPoint) []occultationScreenPoint {
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screen := make([]occultationScreenPoint, len(points))
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for index, point := range points {
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x, y := layout.project(point.longitude, point.latitude)
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screen[index] = occultationScreenPoint{x: x, y: y}
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}
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return simplifyOccultationRing(screen, occultationGeometryTolerancePixels)
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}
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// projectOccultationPolyline 投影并简化一条地理折线。
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func (layout starOccultationSVGLayout) projectOccultationPolyline(points []starOccultationGeoPoint) []occultationScreenPoint {
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screen := make([]occultationScreenPoint, len(points))
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for index, point := range points {
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x, y := layout.project(point.longitude, point.latitude)
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screen[index] = occultationScreenPoint{x: x, y: y}
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}
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return simplifyOccultationPolyline(screen, occultationGeometryTolerancePixels)
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}
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// projectOccultationPathLine 投影并简化一条月掩路径折线。
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func (layout starOccultationSVGLayout) projectOccultationPathLine(points []moon.OccultationPathPoint) []occultationScreenPoint {
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screen := make([]occultationScreenPoint, len(points))
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for index, point := range points {
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x, y := layout.project(point.Longitude, point.Latitude)
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screen[index] = occultationScreenPoint{x: x, y: y}
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}
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return simplifyOccultationPolyline(screen, occultationGeometryTolerancePixels)
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}
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// projectOccultationGeoRing 投影并简化一条地图多边形环。
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func (layout starOccultationSVGLayout) projectOccultationGeoRing(points []geodata.GeoPoint) []occultationScreenPoint {
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screen := make([]occultationScreenPoint, len(points))
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for index, point := range points {
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x, y := layout.project(point.Longitude, point.Latitude)
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screen[index] = occultationScreenPoint{x: x, y: y}
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}
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return simplifyOccultationRing(screen, occultationGeometryTolerancePixels)
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}
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// simplifyOccultationRing 简化闭合环：首点与离首点最远的顶点保留为两个锚点，两段各自简化。
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// 简化后不足三个顶点时返回原环，保证结果仍可填充。
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func simplifyOccultationRing(points []occultationScreenPoint, tolerance float64) []occultationScreenPoint {
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if len(points) < 4 || !(tolerance > 0) {
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return points
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}
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ring := points
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closed := points[0] == points[len(points)-1]
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if closed {
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ring = points[:len(points)-1]
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}
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if len(ring) < 3 {
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return points
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}
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anchor := 1
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farthest := -1.0
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for index := 1; index < len(ring); index++ {
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distance := occultationSquaredDistance(ring[0], ring[index])
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if distance > farthest {
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farthest, anchor = distance, index
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}
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}
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first := simplifyOccultationPolyline(ring[:anchor+1], tolerance)
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second := make([]occultationScreenPoint, len(ring)-anchor+1)
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copy(second, ring[anchor:])
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second[len(second)-1] = ring[0]
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second = simplifyOccultationPolyline(second, tolerance)
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result := make([]occultationScreenPoint, 0, len(first)+len(second)-2)
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result = append(result, first[:len(first)-1]...)
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result = append(result, second[:len(second)-1]...)
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if len(result) < 3 {
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return points
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}
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if closed {
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result = append(result, result[0])
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}
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return result
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}
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// simplifyOccultationPolyline 用 Douglas-Peucker 简化折线，端点恒保留。
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func simplifyOccultationPolyline(points []occultationScreenPoint, tolerance float64) []occultationScreenPoint {
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if len(points) < 3 || !(tolerance > 0) {
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return points
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}
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keep := make([]bool, len(points))
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keep[0], keep[len(points)-1] = true, true
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toleranceSquared := tolerance * tolerance
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type span struct{ first, last int }
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stack := make([]span, 0, 16)
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stack = append(stack, span{first: 0, last: len(points) - 1})
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for len(stack) > 0 {
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current := stack[len(stack)-1]
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stack = stack[:len(stack)-1]
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if current.last <= current.first+1 {
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continue
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}
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index, distance := occultationFarthestVertex(points, current.first, current.last)
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if distance <= toleranceSquared {
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continue
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}
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keep[index] = true
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stack = append(stack, span{first: current.first, last: index}, span{first: index, last: current.last})
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}
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result := make([]occultationScreenPoint, 0, len(points))
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for index, point := range points {
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if keep[index] {
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result = append(result, point)
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}
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}
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return result
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}
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// occultationFarthestVertex 返回首末顶点之间离弦最远的顶点及其平方距离。
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func occultationFarthestVertex(points []occultationScreenPoint, first, last int) (int, float64) {
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best, bestDistance := first, -1.0
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start, end := points[first], points[last]
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for index := first + 1; index < last; index++ {
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distance := occultationChordSquaredDistance(points[index], start, end)
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if distance > bestDistance {
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best, bestDistance = index, distance
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}
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}
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return best, bestDistance
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}
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// occultationChordSquaredDistance 返回点到线段的最短平方距离；线段退化时退化为点距。
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func occultationChordSquaredDistance(point, start, end occultationScreenPoint) float64 {
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dx, dy := end.x-start.x, end.y-start.y
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lengthSquared := dx*dx + dy*dy
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if lengthSquared <= 0 {
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return occultationSquaredDistance(point, start)
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}
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position := ((point.x-start.x)*dx + (point.y-start.y)*dy) / lengthSquared
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if position < 0 {
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position = 0
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} else if position > 1 {
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position = 1
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}
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return occultationSquaredDistance(point, occultationScreenPoint{x: start.x + position*dx, y: start.y + position*dy})
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}
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func occultationSquaredDistance(first, second occultationScreenPoint) float64 {
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dx, dy := first.x-second.x, first.y-second.y
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return dx*dx + dy*dy
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}
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// writeOccultationPathCommands 写出 `M x y L x y ...` 命令序列，坐标保留三位小数。
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func writeOccultationPathCommands(b *strings.Builder, points []occultationScreenPoint) {
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var xBuffer, yBuffer [32]byte
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for index, point := range points {
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if index == 0 {
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b.WriteString("M ")
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} else {
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b.WriteString("L ")
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}
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b.Write(strconv.AppendFloat(xBuffer[:0], point.x, 'f', 3, 64))
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b.WriteByte(' ')
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b.Write(strconv.AppendFloat(yBuffer[:0], point.y, 'f', 3, 64))
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b.WriteByte(' ')
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}
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}
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