package svg
import (
"b612.me/astro/internal/timenote"
"fmt"
"html"
"math"
"strings"
"time"
"b612.me/astro"
"b612.me/astro/basic"
eclipsecore "b612.me/astro/eclipse"
"b612.me/astro/internal/lunarhorizon"
"b612.me/astro/internal/svgchart"
"b612.me/astro/internal/svgmap"
)
const (
lunarEclipseMapDefaultWidth = 960
lunarEclipseMapDefaultHeight = 640
)
// LunarEclipseMapSVGOptions 控制无国界全球可见性地图。
// LunarEclipseMapSVGOptions controls a border-free global visibility map.
type LunarEclipseMapSVGOptions struct {
// Width 和 Height 是 SVG 画布尺寸；宽度小于 640 或高度小于 420 时使用 960x640 默认值。
// Width and Height are SVG canvas dimensions in user units. Width values below 640 and height values below 420 use the 960x640 defaults.
Width int
Height int
// Language 为 "en"（不区分大小写）时使用英文，否则使用中文。
// Language uses English for "en" (case-insensitive) and Chinese otherwise.
Language string
// Location 控制显示的事件时刻；nil 使用 date.Location()。
// Location controls displayed event times. Nil uses date.Location().
Location *time.Location
// TimeScale 选择图中时刻的时标：零值 UTC；TimeScaleUT1 改用 UT1 时刻，此时 Location 必须是
// nil 或 UTC（否则返回 false），并在图注里声明尺度。
// TimeScale selects the label scale: the zero value is UTC; TimeScaleUT1 uses UT1 labels, requires
// Location to be nil or UTC (otherwise the renderer returns false) and declares the scale in the footer.
TimeScale astro.TimeScale
// Projection 选择地图投影；零值使用等经纬投影，不支持的值使渲染器返回 false。
// Projection selects the map projection. The zero value selects the equirectangular projection; unsupported values make the renderer return false.
Projection EclipseMapProjection
// DisablePenumbralPhase 关闭半影阶段，回到只按 P1/P4 分区的四类可见区：零值画半影（补画 U1–U4
// 地平边界、单独着色只看得见半影的月出与月落带「半影月出」「半影月落」，并在时刻行里标出本影接触）。
// DisablePenumbralPhase falls back to the four-way P1/P4-only partition: the zero value draws the
// penumbral phase, adding the U1-U4 horizons, the penumbra-only moonrise and moonset bands as
// separate legend entries, and the umbral contact times.
DisablePenumbralPhase bool
// 空文本字段使用本地化的自动标签。
// Empty text fields use localized automatic labels.
Title string
FooterNote string
}
// LunarEclipseMapSVG 使用默认月食模型绘制全球 P1-P4 可见区域。
// LunarEclipseMapSVG renders the global P1-P4 visibility regions using the default lunar-eclipse model.
func LunarEclipseMapSVG(date time.Time, options LunarEclipseMapSVGOptions) (string, bool) {
return lunarEclipseMapSVG(date, options, eclipsecore.LunarEclipseOnDate)
}
// LunarEclipseMapSVGDanjon 使用 Danjon 模型绘制全球可见区域。
// LunarEclipseMapSVGDanjon renders the global visibility regions with Danjon's model.
func LunarEclipseMapSVGDanjon(date time.Time, options LunarEclipseMapSVGOptions) (string, bool) {
return lunarEclipseMapSVG(date, options, eclipsecore.LunarEclipseOnDateDanjon)
}
// LunarEclipseMapSVGChauvenet 使用 Chauvenet 模型绘制全球可见区域。
// LunarEclipseMapSVGChauvenet renders the global visibility regions with Chauvenet's model.
func LunarEclipseMapSVGChauvenet(date time.Time, options LunarEclipseMapSVGOptions) (string, bool) {
return lunarEclipseMapSVG(date, options, eclipsecore.LunarEclipseOnDateChauvenet)
}
func lunarEclipseMapSVG(
date time.Time,
options LunarEclipseMapSVGOptions,
calculator func(time.Time) (eclipsecore.LunarEclipseInfo, bool),
) (string, bool) {
if !validEclipseMapProjection(options.Projection) {
return "", false
}
info, ok := calculator(date)
if !ok || info.PenumbralStart.IsZero() || info.PenumbralEnd.IsZero() {
return "", false
}
if options.TimeScale == astro.TimeScaleUT1 {
if options.Location != nil && options.Location != time.UTC {
return "", false
}
options.Location = time.UTC
}
options = normalizeLunarEclipseMapSVGOptions(date, options)
projection := internalEclipseMapProjection(options.Projection)
if projection == "" {
projection = svgmap.ProjectionEquirectangular
}
return renderLunarEclipseMapSVG(lunarEclipseDisplayInfo(info, options.TimeScale), info, options, projection), true
}
func normalizeLunarEclipseMapSVGOptions(date time.Time, options LunarEclipseMapSVGOptions) LunarEclipseMapSVGOptions {
if options.Width < 640 {
options.Width = lunarEclipseMapDefaultWidth
}
if options.Height < 420 {
options.Height = lunarEclipseMapDefaultHeight
}
if strings.EqualFold(options.Language, "en") {
options.Language = "en"
} else {
options.Language = "zh"
}
if options.Location == nil {
options.Location = date.Location()
}
return options
}
func renderLunarEclipseMapSVG(
info eclipsecore.LunarEclipseInfo,
geometry eclipsecore.LunarEclipseInfo,
options LunarEclipseMapSVGOptions,
projection svgmap.Projection,
) string {
frame := eclipseMapFrame(options.Width, options.Height, projection, 142, 92)
if projection == svgmap.ProjectionOrthographic {
// 正射视点取食甚时刻的月下点：视点固定 (0°,0°) 会把半个可见半球让给与本次月食无关的区域。
frame.CenterLongitude, frame.CenterLatitude = lunarEclipseOrthographicCenter(geometry.Maximum)
}
title := options.Title
if title == "" {
date := info.Maximum.In(options.Location).Format("2006-01-02")
if options.Language == "en" {
title = fmt.Sprintf("%s %s Global Visibility", date, lunarEclipseSVGTypeName(info.Type, "en"))
} else {
title = fmt.Sprintf("%s %s全球可见图", date, lunarEclipseSVGTypeName(info.Type, "zh"))
}
}
var builder strings.Builder
fmt.Fprintf(&builder, ``)
return builder.String()
}
// lunarEclipseMapDrawsPenumbralBands 只在该场月食确有本影阶段且开关打开时才区分半影带。
func lunarEclipseMapDrawsPenumbralBands(info eclipsecore.LunarEclipseInfo, includePenumbral bool) bool {
return includePenumbral && info.HasPartial
}
// 可见性由 P1、食甚、P4 三刻的月球地平状态共同界定：全程可见要求三刻都在地平上，
// 只在食甚前后露出地平的地点仍看得见本影食，算带食月落；三刻都不见才算不可见。
func writeLunarEclipseVisibilityMasks(builder *strings.Builder, frame svgmap.Frame) {
writeLunarEclipseVisibilityMask(builder, "lunar-not-visible-mask", frame,
"lunar-visible-p1-shape", "lunar-visible-p4-shape", "lunar-visible-maximum-shape")
writeLunarEclipseVisibilityMask(builder, "lunar-not-p1-p4-mask", frame,
"lunar-visible-p1-shape", "lunar-visible-p4-shape")
writeLunarEclipseVisibilityMask(builder, "lunar-not-maximum-mask", frame, "lunar-visible-maximum-shape")
writeLunarEclipseVisibilityMask(builder, "lunar-not-p4-mask", frame, "lunar-visible-p4-shape")
writeLunarEclipseVisibilityMask(builder, "lunar-not-p1-mask", frame, "lunar-visible-p1-shape")
}
func writeLunarEclipseVisibilityMask(
builder *strings.Builder,
id string,
frame svgmap.Frame,
excludedShapeIDs ...string,
) {
fmt.Fprintf(builder, ``,
id, frame.X, frame.Y, frame.Width, frame.Height)
fmt.Fprintf(builder, ``,
frame.X, frame.Y, frame.Width, frame.Height)
for _, shapeID := range excludedShapeIDs {
fmt.Fprintf(builder, ``, shapeID)
}
builder.WriteString(``)
}
func eclipseMapFrame(width, height int, projection svgmap.Projection, top, bottom float64) svgmap.Frame {
availableWidth := float64(width) - 90
availableHeight := float64(height) - top - bottom
mapWidth := math.Min(availableWidth, availableHeight*2)
mapHeight := mapWidth / 2
if projection != svgmap.ProjectionEquirectangular {
mapWidth = math.Min(availableWidth, availableHeight)
mapHeight = mapWidth
}
return svgmap.Frame{
X: (float64(width) - mapWidth) / 2,
Y: top,
Width: mapWidth,
Height: mapHeight,
Projection: projection,
}
}
func lunarEclipseVisibilityPath(value time.Time, frame svgmap.Frame) (string, []svgmap.GeoPoint) {
points := basic.MoonHorizon(basic.Date2JD(value.UTC()), 360)
boundary := make([]svgmap.GeoPoint, len(points))
for index, point := range points {
boundary[index] = svgmap.GeoPoint{Longitude: point[0], Latitude: point[1]}
}
if frame.Projection == svgmap.ProjectionEquirectangular {
// 等距圆柱投影在高纬把经度拉伸：1° 的球面地平弧在极点附近可以横跨近 180° 经度，
// 只连端点会在极区切出地平线以外的假可见帽（1904-09-24 实测 −0.054°，约 6 km）。
// 极射投影没有这个畸变，保持原输出。
// Equirectangular projection stretches longitude near a pole: a 1-degree spherical
// horizon arc can span almost 180 degrees there, so joining endpoints alone cuts a fake
// visible cap outside the horizon (measured -0.054 deg, about 6 km, on 1904-09-24).
// Polar projections have no such distortion and keep their existing output.
// 门限取画布上约 0.03 像素：极区细分再多也画不出来，而 GeoJSON 用的 0.002°
// 在 812 像素宽的世界图上相当于 0.005 像素，会让 SVG 无谓地大三分之一。
// The tolerance is about 0.03 pixel on the canvas: finer subdivision cannot be drawn,
// while the GeoJSON tolerance of 0.002 deg is 0.005 pixel on this 812-pixel-wide world
// map and would inflate the SVG by a third for nothing.
tolerance := 0.03 * 360 / frame.Width
if tolerance < lunarhorizon.DefaultToleranceDegrees {
tolerance = lunarhorizon.DefaultToleranceDegrees
}
boundary = lunarhorizon.RefineWithin(boundary, value, tolerance)
}
closedBoundary := append(append([]svgmap.GeoPoint(nil), boundary...), boundary[0])
return lunarEclipseGeoPolygonPath(boundary, frame), closedBoundary
}
// lunarEclipseGeoPolygonPath 把经纬度环投影成 SVG 面路径，反经线与画布边缘按共享片段切开。
func lunarEclipseGeoPolygonPath(boundary []svgmap.GeoPoint, frame svgmap.Frame) string {
var builder strings.Builder
for _, fragment := range svgmap.PolygonFragments(boundary, frame.Clip()) {
if frame.IsPolar() {
fragment = lunarEclipsePolarHorizonClosure(fragment)
}
appendEclipseMapPolygonPathConsistent(&builder, frame, fragment)
}
return builder.String()
}
func lunarEclipsePolarHorizonClosure(points []svgmap.GeoPoint) []svgmap.GeoPoint {
var result []svgmap.GeoPoint
for index, point := range points {
result = append(result, point)
next := points[(index+1)%len(points)]
if math.Abs(point.Latitude) > 1e-9 || math.Abs(next.Latitude) > 1e-9 {
continue
}
// The equatorial clipping edge is an arc on a polar map, not a chord.
// The Moon-visible part of the equator is always the minor arc.
delta := math.Remainder(next.Longitude-point.Longitude, 360)
steps := int(math.Ceil(math.Abs(delta)))
for step := 1; step < steps; step++ {
result = append(result, svgmap.GeoPoint{Longitude: point.Longitude + delta*float64(step)/float64(steps)})
}
}
return result
}
func appendEclipseMapPolygonPath(builder *strings.Builder, frame svgmap.Frame, points []svgmap.GeoPoint) {
if len(points) < 3 {
return
}
for index, point := range points {
x, y, ok := frame.Project(point.Longitude, point.Latitude)
if !ok {
continue
}
command := "L"
if index == 0 {
command = "M"
}
fmt.Fprintf(builder, `%s %.3f %.3f `, command, x, y)
}
builder.WriteString(`Z `)
}
func writeEclipseMapGeoLine(
builder *strings.Builder,
frame svgmap.Frame,
points []svgmap.GeoPoint,
className, color string,
strokeWidth float64,
dash, clipID, dataSource string,
) {
for _, segment := range svgmap.PolylineSegments(points, frame.Clip()) {
if len(segment) < 2 {
continue
}
fmt.Fprintf(builder, ``,
clipID, source, color, strokeWidth, dash)
}
}
func writeLunarEclipseUnavailableRegion(builder *strings.Builder, frame svgmap.Frame) {
if frame.IsPolar() {
fmt.Fprintf(builder, ``,
frame.X+frame.Width/2, frame.Y+frame.Height/2, frame.Width/2)
return
}
fmt.Fprintf(builder, ``,
frame.X, frame.Y, frame.Width, frame.Height)
}
func writeLunarEclipseMapSummary(builder *strings.Builder, info eclipsecore.LunarEclipseInfo, options LunarEclipseMapSVGOptions) {
start := info.PenumbralStart.In(options.Location)
maximum := info.Maximum.In(options.Location)
end := info.PenumbralEnd.In(options.Location)
zone, _ := maximum.Zone()
if zone == "" {
zone = "UTC"
}
text := fmt.Sprintf("P1 %s | 食甚 %s | P4 %s (%s) | 半影食分 %.3f | 本影食分 %.3f",
start.Format("15:04:05"), maximum.Format("15:04:05"), end.Format("15:04:05"), zone,
info.PenumbralMagnitude, info.UmbralMagnitude)
if options.Language == "en" {
text = fmt.Sprintf("P1 %s | Greatest %s | P4 %s (%s) | penumbral magnitude %.3f | umbral magnitude %.3f",
start.Format("15:04:05"), maximum.Format("15:04:05"), end.Format("15:04:05"), zone,
info.PenumbralMagnitude, info.UmbralMagnitude)
}
fmt.Fprintf(builder, `%s`,
float64(options.Width)/2, html.EscapeString(text))
if line := lunarEclipseMapUmbralContactLine(info, options); line != "" {
fmt.Fprintf(builder, `%s`,
float64(options.Width)/2, html.EscapeString(line))
}
}
// lunarEclipseMapUmbralContactLine 给出本影接触时刻行；开关关闭或没有本影阶段时返回空串。
func lunarEclipseMapUmbralContactLine(info eclipsecore.LunarEclipseInfo, options LunarEclipseMapSVGOptions) string {
if options.DisablePenumbralPhase || !info.HasPartial {
return ""
}
parts := []string{"U1 " + info.PartialStart.In(options.Location).Format("15:04:05")}
if info.HasTotal {
parts = append(parts,
"U2 "+info.TotalStart.In(options.Location).Format("15:04:05"),
"U3 "+info.TotalEnd.In(options.Location).Format("15:04:05"))
}
parts = append(parts, "U4 "+info.PartialEnd.In(options.Location).Format("15:04:05"))
prefix := "本影阶段 "
if options.Language == "en" {
prefix = "Umbral phases "
}
return prefix + strings.Join(parts, " | ")
}
// lunarEclipseMapLegendRows 给出可见性图例的标注位次：每行按实测文本宽度排布并居中在地图框下方。
func lunarEclipseMapLegendRows(frame svgmap.Frame, canvasWidth float64, language string, penumbralBands bool) [][]solarEclipseCardinalLabel {
labels := []string{"全程可见", "带食月出", "带食月落", "不可见"}
if language == "en" {
labels = []string{"Entire eclipse", "Moonrise during eclipse", "Moonset during eclipse", "Not visible"}
}
if penumbralBands {
moonrise, moonset := "半影月出", "半影月落"
if language == "en" {
moonrise, moonset = "Penumbra moonrise", "Penumbra moonset"
}
labels = []string{labels[0], labels[1], moonrise, labels[2], moonset, labels[3]}
}
width := func(text string) float64 {
return lunarEclipseDetailedMapLegendIconWidth +
svgchart.EstimatedTextWidth(text, lunarEclipseDetailedMapLegendFontSize)
}
available := canvasWidth - 2*lunarEclipseDetailedPageInset
packed := make([][]string, 0, 2)
current := make([]string, 0, len(labels))
used := 0.0
for _, label := range labels {
item := width(label)
next := item
if len(current) > 0 {
next = used + lunarEclipseDetailedMapLegendGap + item
if next > available {
packed = append(packed, current)
current = make([]string, 0, len(labels))
next = item
}
}
current = append(current, label)
used = next
}
if len(current) > 0 {
packed = append(packed, current)
}
centreX := frame.X + frame.Width/2
baseY := frame.Y + frame.Height + 31
rows := make([][]solarEclipseCardinalLabel, 0, len(packed))
for index, row := range packed {
total := 0.0
for position, label := range row {
if position > 0 {
total += lunarEclipseDetailedMapLegendGap
}
total += width(label)
}
x := centreX - total/2
if x < lunarEclipseDetailedPageInset {
x = lunarEclipseDetailedPageInset
}
if limit := canvasWidth - lunarEclipseDetailedPageInset - total; x > limit {
x = limit
}
entries := make([]solarEclipseCardinalLabel, 0, len(row))
for _, label := range row {
entries = append(entries, solarEclipseCardinalLabel{
text: label,
x: x + lunarEclipseDetailedMapLegendIconWidth,
y: baseY + float64(index)*lunarEclipseDetailedMapLegendLineStep,
})
x += width(label) + lunarEclipseDetailedMapLegendGap
}
rows = append(rows, entries)
}
return rows
}
func writeLunarEclipseMapLegend(builder *strings.Builder, frame svgmap.Frame, canvasWidth float64, language string, penumbralBands bool) {
colors := []string{"#5e846d", "#4e9da0", "#e2aa4b", "#747b7d"}
if penumbralBands {
colors = []string{"#5e846d", "#4e9da0", "#7488cc", "#e2aa4b", "#ab7fb5", "#747b7d"}
}
index := 0
for _, row := range lunarEclipseMapLegendRows(frame, canvasWidth, language, penumbralBands) {
for _, entry := range row {
color := colors[0]
if index < len(colors) {
color = colors[index]
}
fmt.Fprintf(builder, ``,
entry.x-lunarEclipseDetailedMapLegendIconWidth, entry.y-8, color)
fmt.Fprintf(builder, `%s`,
entry.x, entry.y, lunarEclipseDetailedMapLegendFontSize, html.EscapeString(entry.text))
index++
}
}
}
func writeLunarEclipseMapFooter(
builder *strings.Builder,
frame svgmap.Frame,
options LunarEclipseMapSVGOptions,
projection svgmap.Projection,
instant time.Time,
legendRows int,
) {
text := options.FooterNote
if text == "" {
if options.Language == "en" {
text = eclipseMapProjectionLabel(projection, "en") + "; P1/P4 Moon-visible hemispheres; Natural Earth 1:50m physical land, no administrative boundaries."
} else {
text = eclipseMapProjectionLabel(projection, "zh") + "；按 P1/P4 月球可见半球分区；Natural Earth 1:50m 物理陆地底图，不含行政边界。"
}
}
// 页脚末行要落在白色图框内：图框在画布内缩 18px，11px 字的末行基线留 26px（框线 + 间隙 + 字下伸部）。
const footerBottomPadding = 28.0
// 首行基线再让出一个字下伸部，末行才刚好落在留白之上（BaselineLineLimit 按行下沿计行）。
baseline := float64(options.Height) - footerBottomPadding - svgchart.FooterLineHeight(11) - 4
// 图例换成多行时页脚要跟着下移，否则窄画布上两行文字会叠在一起；下行仍留在图框内。
if legendRows > 1 {
if shifted := frame.Y + frame.Height + 31 + float64(legendRows-1)*lunarEclipseDetailedMapLegendLineStep + 15; shifted > baseline {
baseline = math.Min(shifted, float64(options.Height)-footerBottomPadding)
}
}
// 默认说明是单行；调用方文本按图框宽度折行，行数按画布底边截断，首行位置不变。
note := timenote.Scale(options.TimeScale, instant, options.Location, options.Language)
lines := []string{text}
if options.FooterNote != "" {
lines = svgchart.WrapText(options.FooterNote, float64(options.Width)-frame.X-24, 11)
}
lines = svgchart.FooterLinesWithScale(lines, note, float64(options.Width)-frame.X-24, 11,
svgchart.BaselineLineLimit(11, svgchart.FooterLineHeight(11), baseline,
float64(options.Height)-footerBottomPadding))
for index, line := range lines {
fmt.Fprintf(builder, `%s`,
frame.X, baseline+float64(index)*svgchart.FooterLineHeight(11), html.EscapeString(line))
}
}
func normalizeDegree180(value float64) float64 {
value = math.Mod(value+180, 360)
if value < 0 {
value += 360
}
return value - 180
}
// lunarEclipseOrthographicCenter 给出月食正射图的视点：食甚时刻的月下点（月球位于天顶的地点）。
func lunarEclipseOrthographicCenter(at time.Time) (float64, float64) {
jd := basic.Date2JD(at.UTC())
tt := basic.UTC2TT(jd)
ra, dec := basic.HMoonTrueRaDec(tt)
return normalizeDegree180(ra - basic.ApparentSiderealTime(basic.TT2UT1(tt))*15), dec
}
// writeLunarEclipseMapDefinitions 输出四类可见性区域所需的形状与掩膜定义。
// 独立全球图和 详细版式组合图共用，形状按传入的图框重建。
func writeLunarEclipseMapDefinitions(b *strings.Builder, frame svgmap.Frame, info eclipsecore.LunarEclipseInfo, penumbralBands bool) {
b.WriteString(frame.ClipDefinition("lunar-map-clip"))
startPath, _ := lunarEclipseVisibilityPath(info.PenumbralStart, frame)
endPath, _ := lunarEclipseVisibilityPath(info.PenumbralEnd, frame)
maximumPath, _ := lunarEclipseVisibilityPath(info.Maximum, frame)
fmt.Fprintf(b, ``, startPath)
fmt.Fprintf(b, ``, endPath)
fmt.Fprintf(b, ``, maximumPath)
b.WriteString(``)
b.WriteString(``)
writeLunarEclipseVisibilityMasks(b, frame)
if penumbralBands {
writeLunarEclipseUmbralVisibilityShapes(b, frame, info)
}
}
// writeLunarEclipseUmbralVisibilityShapes 输出 U1、U4 的月球可见半球形状，以及"本影阶段任意时刻
// 在地平上"的取样半球、裁剪路径与排除掩膜；底带取并集内部，半影带取外部。
func writeLunarEclipseUmbralVisibilityShapes(b *strings.Builder, frame svgmap.Frame, info eclipsecore.LunarEclipseInfo) {
u1Path, _ := lunarEclipseVisibilityPath(info.PartialStart, frame)
u4Path, _ := lunarEclipseVisibilityPath(info.PartialEnd, frame)
fmt.Fprintf(b, ``, u1Path)
fmt.Fprintf(b, ``, u4Path)
b.WriteString(``)
b.WriteString(``)
writeLunarEclipseUmbralVisibleShapes(b, frame, info)
}
// writeLunarEclipseUmbralVisibleShapes 输出"本影阶段任意时刻在地平上"的取样半球：本影区间按固定档位
// 取样，每一刻的可见半球都是一个精确的圆盘（按经纬度插值会把近乎子午线方向的边界切进真实区域——
// 实测 1932-03-22 西经 75.5° 一带上边界 0.5° 经度内从 +19.9° 掉到 −27.2°，1° 列的弦会切掉十几度）。
// 这些形状同时用于底带的裁剪（取并集）与半影带的掩膜（取补集），两侧严丝合缝。
func writeLunarEclipseUmbralVisibleShapes(b *strings.Builder, frame svgmap.Frame, info eclipsecore.LunarEclipseInfo) {
instants := lunarEclipseUmbralVisibilityInstants(info)
if len(instants) == 0 {
// 兜底：算不出本影可见区时至少挖掉两端接触（宁可少扣，也不让底带无裁剪地铺满）。
b.WriteString(``)
writeLunarEclipseVisibilityMask(b, "lunar-not-umbral-visible-mask", frame,
"lunar-visible-u1-shape", "lunar-visible-u4-shape")
return
}
// 两端复用已经写好的精细半球形状，中间的取样用粗轮廓：单个圆盘在球面上的偏差约 0.035°，
// 在 1200 像素宽的世界图上不到 0.1 像素，而每个形状能省下三分之二的字节。
ids := []string{"lunar-visible-u1-shape"}
for index := 1; index < len(instants)-1; index++ {
id := fmt.Sprintf("lunar-visible-umbral-%d", index)
fmt.Fprintf(b, ``, id, lunarEclipseMaskHorizonPath(instants[index], frame))
ids = append(ids, id)
}
ids = append(ids, "lunar-visible-u4-shape")
var clip strings.Builder
clip.WriteString(``)
for _, id := range ids {
fmt.Fprintf(&clip, ``, id)
}
clip.WriteString(``)
b.WriteString(clip.String())
writeLunarEclipseVisibilityMask(b, "lunar-not-umbral-visible-mask", frame, ids...)
}
// lunarEclipseMaskHorizonPath 掩膜用的可见半球轮廓：90 点基础圆，等距圆柱投影下再按 0.2° 容差
// 细化，避免极区一段地平弧投影后横跨近 180° 经度、弦切出地平线以外的假可见帽。
func lunarEclipseMaskHorizonPath(value time.Time, frame svgmap.Frame) string {
points := basic.MoonHorizon(basic.Date2JD(value.UTC()), 90)
boundary := make([]svgmap.GeoPoint, len(points))
for index, point := range points {
boundary[index] = svgmap.GeoPoint{Longitude: point[0], Latitude: point[1]}
}
if frame.Projection == svgmap.ProjectionEquirectangular {
boundary = lunarhorizon.RefineWithin(boundary, value, 0.2)
}
return lunarEclipseGeoPolygonPath(boundary, frame)
}
// lunarEclipseUmbralVisibilityInstants 本影区间按 15 分钟档位取样，至少两端、至多 12 刻：中间取样用
// 粗轮廓，圆盘分辨率约 0.035°，合起来残余的掠射窗口深度约 0.05°（约 0.15 像素）；要逐点精确判定
// 请用站点 API 或 GeoJSON。
func lunarEclipseUmbralVisibilityInstants(info eclipsecore.LunarEclipseInfo) []time.Time {
const (
step = 15 * time.Minute
limit = 12
)
duration := info.PartialEnd.Sub(info.PartialStart)
if duration <= 0 {
return nil
}
count := int(duration/step) + 1
if count < 2 {
count = 2
}
if count > limit {
count = limit
}
instants := make([]time.Time, count)
for index := range instants {
instants[index] = info.PartialStart.Add(duration * time.Duration(index) / time.Duration(count-1))
}
return instants
}
func writeLunarEclipseMapRegions(b *strings.Builder, frame svgmap.Frame, info eclipsecore.LunarEclipseInfo, penumbralBands bool) {
_, startBoundary := lunarEclipseVisibilityPath(info.PenumbralStart, frame)
_, endBoundary := lunarEclipseVisibilityPath(info.PenumbralEnd, frame)
frame.WriteOcean(b)
frame.WriteGraticule(b, "lunar-map-clip")
frame.WriteLand(b, "lunar-map-clip")
fmt.Fprintf(b, ``, eclipseMapSourceLunarVisibilityRegions)
writeLunarEclipseUnavailableRegion(b, frame)
writeLunarEclipseBaseRegion(b, penumbralBands, "lunar-visible-umbral",
``)
writeLunarEclipseBaseRegion(b, penumbralBands, "lunar-visible-umbral",
``)
b.WriteString(``)
// 两端可见、食甚却在地平下的高纬月落-月出带：两端可见推不出全程可见，归入带食月落。
b.WriteString(``)
// 两端都在地平下、只有食甚前后在地平上的极区透镜：月落必然落在食甚之后，与带食月落同类着色。
b.WriteString(``)
if penumbralBands {
writeLunarEclipsePenumbralRegions(b)
}
b.WriteString(``)
writeEclipseMapGeoLine(b, frame, startBoundary, "p1-horizon", "#a56c16", 1.2, "4 3", "lunar-map-clip", eclipseMapSourceLunarHorizonBoundaries)
writeEclipseMapGeoLine(b, frame, endBoundary, "p4-horizon", "#197a82", 1.2, "4 3", "lunar-map-clip", eclipseMapSourceLunarHorizonBoundaries)
if penumbralBands {
writeLunarEclipseUmbralHorizonLines(b, frame, info)
}
}
// writeLunarEclipseBaseRegion 画一条月出/月落底带；半影带开启时只保留"本影阶段真的能看见"的部分，
// 半影段交给半影带：两条带用同一区域的正反面裁切，既不叠色也不留缝。
func writeLunarEclipseBaseRegion(b *strings.Builder, penumbralBands bool, clip, element string) {
if penumbralBands {
fmt.Fprintf(b, `%s`, clip, element)
return
}
b.WriteString(element)
}
// writeLunarEclipsePenumbralRegions 只着色只看得见半影的两条带（月落侧与月出侧）：主端在地平上，
// 本影阶段整段在地平下，再扣掉另一端的可见区（极区下中天会让两端同时可见）。
func writeLunarEclipsePenumbralRegions(b *strings.Builder) {
b.WriteString(``)
b.WriteString(``)
}
// writeLunarEclipseUmbralHorizonLines 补画本影接触点的地平边界，边界之间就是各阶段被月出月落切掉的区间。
func writeLunarEclipseUmbralHorizonLines(b *strings.Builder, frame svgmap.Frame, info eclipsecore.LunarEclipseInfo) {
type horizonContact struct {
class string
at time.Time
}
contacts := []horizonContact{{"u1-horizon", info.PartialStart}}
if info.HasTotal {
contacts = append(contacts, horizonContact{"u2-horizon", info.TotalStart}, horizonContact{"u3-horizon", info.TotalEnd})
}
contacts = append(contacts, horizonContact{"u4-horizon", info.PartialEnd})
for _, contact := range contacts {
if contact.at.IsZero() {
continue
}
_, boundary := lunarEclipseVisibilityPath(contact.at, frame)
writeEclipseMapGeoLine(b, frame, boundary, contact.class, "#5f4b8b", 1.1, "3 3", "lunar-map-clip", eclipseMapSourceLunarHorizonBoundaries)
}
}
// lunarEclipseInfoUT1Labels 把民用时刻换成同一物理时刻的 UT1 时刻。零值 time.Time 表示该阶段