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astro/eclipse/svg/transit_map.go
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feat: 引入可切换星历模型并扩展天象观测链路
2026-10-15 23:54:15 +08:00
package svg
import (
"fmt"
"html"
"math"
"strings"
"time"
"b612.me/astro"
"b612.me/astro/basic"
"b612.me/astro/internal/geodata"
"b612.me/astro/internal/svgchart"
"b612.me/astro/internal/svgmap"
"b612.me/astro/internal/timenote"
)
const (
transitMapDefaultWidth = 960
transitMapDefaultHeight = 640
)
// TransitPlanet 选择凌日行星 / selects the transiting planet.
type TransitPlanet int
const (
// TransitMercury 是水星凌日 / Mercury transit.
TransitMercury TransitPlanet = 1
// TransitVenus 是金星凌日 / Venus transit.
TransitVenus TransitPlanet = 2
)
// TransitIsochrones 是等时线开关的位组合 / bit set of contact isochrones.
type TransitIsochrones uint8
const (
// TransitIsochroneC1 画一触等时线 / draw C1 isochrones.
TransitIsochroneC1 TransitIsochrones = 1 << iota
// TransitIsochroneC2 画二触等时线；掠凌没有内切接触时忽略 / draw C2 isochrones, ignored for a grazing transit.
TransitIsochroneC2
// TransitIsochroneC3 画三触等时线；掠凌没有内切接触时忽略 / draw C3 isochrones, ignored for a grazing transit.
TransitIsochroneC3
// TransitIsochroneC4 画四触等时线 / draw C4 isochrones.
TransitIsochroneC4
// TransitIsochroneExternal 是一触与四触 / C1 and C4.
TransitIsochroneExternal = TransitIsochroneC1 | TransitIsochroneC4
// TransitIsochroneAll 是全部四个接触 / all four contacts.
TransitIsochroneAll = TransitIsochroneC1 | TransitIsochroneC2 | TransitIsochroneC3 | TransitIsochroneC4
)
// TransitMapSVGOptions 控制全球凌日可见图。
// TransitMapSVGOptions controls a global planetary-transit visibility map.
type TransitMapSVGOptions 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. 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 要求 Location 为 nil 或 UTC，否则返回 false。
// TimeScale selects the label scale: the zero value is UTC; TimeScaleUT1 requires Location to be nil or UTC, otherwise the renderer returns false.
TimeScale astro.TimeScale
// Projection 选择地图投影；零值使用等经纬投影，正射投影视点取凌甚时的太阳直射点。
// Projection selects the map projection. The zero value uses equirectangular; orthographic centres on the subsolar point at greatest.
Projection EclipseMapProjection
// Isochrones 选择要画的站心接触等时线，可按位组合；零值不画（默认关闭，需显式开启）。
// Isochrones selects the topocentric contact isochrones to draw and may combine flags. The zero value draws none (off by default).
Isochrones TransitIsochrones
// IsochroneStep 是等时线的时间间隔；非正值按行星自动取（水星 20 秒、金星 1 分钟）。
// IsochroneStep is the isochrone spacing. Non-positive values select 20 s for Mercury and 1 min for Venus.
IsochroneStep time.Duration
// 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
}
// TransitMapSVG 绘制距 date 最近一次水星或金星凌日的全球可见图：按一触、凌甚、四触太阳中心在视地平上
// （计入标准大气折射）的区域分区；Options.Isochrones 显式开启时叠加所选接触的站心等时线。找不到凌日或选项无效时返回 false。
// TransitMapSVG renders the global visibility of the Mercury or Venus transit closest to date: regions follow where the
// Sun's centre is above the apparent horizon (standard refraction) at C1, greatest and C4. Topocentric isochrones of the
// selected contacts are overlaid only when Options.Isochrones enables them. It returns false when no transit is found
// or the options are invalid.
func TransitMapSVG(planet TransitPlanet, date time.Time, options TransitMapSVGOptions) (string, bool) {
transit, ok := closestPlanetTransit(planet, date)
if !ok || !validEclipseMapProjection(options.Projection) {
return "", false
}
if options.TimeScale == astro.TimeScaleUT1 {
if options.Location != nil && options.Location != time.UTC {
return "", false
}
options.Location = time.UTC
}
options = normalizeTransitMapSVGOptions(date, options)
if !transit.HasInternal {
options.Isochrones &^= TransitIsochroneC2 | TransitIsochroneC3
}
options.Isochrones &= TransitIsochroneAll
if options.IsochroneStep <= 0 {
options.IsochroneStep = time.Minute
if planet == TransitMercury {
options.IsochroneStep = 20 * time.Second
}
}
projection := internalEclipseMapProjection(options.Projection)
if projection == "" {
projection = svgmap.ProjectionEquirectangular
}
return renderTransitMapSVG(planet, transit, options, projection), true
}
// closestPlanetTransit 返回距 date 最近的一次地心凌日；行星无效或找不到时第二个返回值为 false。
func closestPlanetTransit(planet TransitPlanet, date time.Time) (basic.PlanetTransitResult, bool) {
jd := basic.Date2JD(date.UTC())
var transit basic.PlanetTransitResult
switch planet {
case TransitMercury:
transit = basic.ClosestMercuryTransit(jd)
case TransitVenus:
transit = basic.ClosestVenusTransit(jd)
default:
return transit, false
}
return transit, transit.Valid
}
func normalizeTransitMapSVGOptions(date time.Time, options TransitMapSVGOptions) TransitMapSVGOptions {
if options.Width < 640 {
options.Width = transitMapDefaultWidth
}
if options.Height < 420 {
options.Height = transitMapDefaultHeight
}
if strings.EqualFold(options.Language, "en") {
options.Language = "en"
} else {
options.Language = "zh"
}
if options.Location == nil {
options.Location = date.Location()
}
return options
}
// transitMapContacts 是地心一触、凌甚、四触的 UTC 时刻。
type transitMapContacts struct {
start, greatest, end time.Time
internalStart, internalEnd time.Time
hasInternal bool
}
func transitMapContactsOf(transit basic.PlanetTransitResult) transitMapContacts {
at := func(jd float64) time.Time { return basic.JD2DateByZone(jd, time.UTC, false) }
contacts := transitMapContacts{
start: at(transit.ExternalIngress),
greatest: at(transit.Greatest),
end: at(transit.ExternalEgress),
hasInternal: transit.HasInternal,
}
if transit.HasInternal {
contacts.internalStart, contacts.internalEnd = at(transit.InternalIngress), at(transit.InternalEgress)
}
return contacts
}
func renderTransitMapSVG(
planet TransitPlanet,
transit basic.PlanetTransitResult,
options TransitMapSVGOptions,
projection svgmap.Projection,
) string {
contacts := transitMapContactsOf(transit)
// 底部比月食图多留两行：图例下要放可折行的说明与时标声明。
frame := eclipseMapFrame(options.Width, options.Height, projection, 142, 122)
if projection == svgmap.ProjectionOrthographic {
center := solarEclipseSubsolarPoint(contacts.greatest)
frame.CenterLongitude, frame.CenterLatitude = center.Longitude, center.Latitude
}
title := options.Title
if title == "" {
date := transitMapDisplayTime(contacts.greatest, options).Format("2006-01-02")
if options.Language == "en" {
title = fmt.Sprintf("%s Transit of %s Global Visibility", date, transitMapPlanetName(planet, "en"))
} else {
title = fmt.Sprintf("%s %s凌日全球可见图", date, transitMapPlanetName(planet, "zh"))
}
}
var b strings.Builder
fmt.Fprintf(&b, `<svg xmlns="http://www.w3.org/2000/svg" width="%d" height="%d" viewBox="0 0 %d %d" role="img" aria-label="%s">`,
options.Width, options.Height, options.Width, options.Height, html.EscapeString(title))
b.WriteString(`<defs>`)
writeTransitMapDefinitions(&b, frame, contacts)
b.WriteString(`</defs>`)
b.WriteString(`<rect width="100%" height="100%" fill="#efefed"/>`)
fmt.Fprintf(&b, `<rect x="22" y="18" width="%d" height="%d" fill="#ffffff" stroke="#c9c9c6" stroke-width="1.2"/>`,
options.Width-44, options.Height-36)
titleText := title
if options.Title != "" {
titleText = svgchart.EllipsizeText(title, float64(options.Width)-52, 24)
}
fmt.Fprintf(&b, `<text x="%.3f" y="47" fill="#111111" font-family="Georgia, 'Times New Roman', serif" font-size="24" font-weight="700" text-anchor="middle">%s</text>`,
float64(options.Width)/2, html.EscapeString(titleText))
writeTransitMapSummary(&b, transit, contacts, options)
frame.WriteOcean(&b)
frame.WriteGraticule(&b, "transit-map-clip")
frame.WriteLand(&b, "transit-map-clip")
writeTransitMapRegions(&b, frame, contacts)
if options.Isochrones != 0 {
writeTransitMapIsochrones(&b, frame, transit, options)
}
frame.WriteFrame(&b)
legendRows := writeTransitMapLegend(&b, frame, float64(options.Width), options)
writeTransitMapFooter(&b, frame, options, projection, contacts.greatest, legendRows)
b.WriteString(`</svg>`)
return b.String()
}
func transitMapPlanetName(planet TransitPlanet, language string) string {
if language == "en" {
if planet == TransitMercury {
return "Mercury"
}
return "Venus"
}
if planet == TransitMercury {
return "水星"
}
return "金星"
}
// transitMapDisplayTime 把 UTC 时刻换成图上显示的时刻：UT1 时标给 UT1 读数，否则换到 Location。
func transitMapDisplayTime(value time.Time, options TransitMapSVGOptions) time.Time {
return transitDisplayTime(value, options.TimeScale, options.Location)
}
// transitMapSunUpPath 返回 value 时刻太阳中心在视地平上的区域面路径（evenodd）与地平边界。
// 视地平计入标准大气折射：太阳中心距直射点小于 90°+34′ 即可见，太阳视差 8.8″ 忽略。
// 半径超过 90° 的球冠环在拆分日界线时分不清内外，所以改画对日点为心、半径不足 90° 的不可见冠，
// 再用图框减去它得到可见区。
func transitMapSunUpPath(value time.Time, frame svgmap.Frame) (string, []svgmap.GeoPoint) {
subsolar := solarEclipseSubsolarPoint(value)
antisolar := svgmap.GeoPoint{Longitude: geodata.NormalizeLongitude(subsolar.Longitude + 180), Latitude: -subsolar.Latitude}
radius := 90 - basic.RefractionFromApparentAltitude(0, transitMapRefractionPressureHPa, transitMapRefractionTemperatureC)
boundary := geodata.SphericalCircle(antisolar, radius, 360)
closed := append(append([]svgmap.GeoPoint(nil), boundary...), boundary[0])
path := fmt.Sprintf("M %.3f %.3f H %.3f V %.3f H %.3f Z %s",
frame.X, frame.Y, frame.X+frame.Width, frame.Y+frame.Height, frame.X, lunarEclipseGeoPolygonPath(boundary, frame))
return path, closed
}
// 标准大气，与 basic 站心凌日的视地平判定一致。
const (
transitMapRefractionPressureHPa = 1010.0
transitMapRefractionTemperatureC = 10.0
)
// writeTransitMapDefinitions 输出一触、凌甚、四触三个太阳在地平上半球的形状与排除掩膜，分区口径同月食可见图。
func writeTransitMapDefinitions(b *strings.Builder, frame svgmap.Frame, contacts transitMapContacts) {
b.WriteString(frame.ClipDefinition("transit-map-clip"))
startPath, _ := transitMapSunUpPath(contacts.start, frame)
endPath, _ := transitMapSunUpPath(contacts.end, frame)
greatestPath, _ := transitMapSunUpPath(contacts.greatest, frame)
fmt.Fprintf(b, `<path id="transit-sun-c1-shape" fill-rule="evenodd" clip-rule="evenodd" d="%s"/>`, startPath)
fmt.Fprintf(b, `<path id="transit-sun-c4-shape" fill-rule="evenodd" clip-rule="evenodd" d="%s"/>`, endPath)
fmt.Fprintf(b, `<path id="transit-sun-greatest-shape" fill-rule="evenodd" clip-rule="evenodd" d="%s"/>`, greatestPath)
b.WriteString(`<clipPath id="transit-sun-c4"><use href="#transit-sun-c4-shape"/></clipPath>`)
b.WriteString(`<clipPath id="transit-sun-greatest"><use href="#transit-sun-greatest-shape"/></clipPath>`)
writeLunarEclipseVisibilityMask(b, "transit-not-visible-mask", frame,
"transit-sun-c1-shape", "transit-sun-c4-shape", "transit-sun-greatest-shape")
writeLunarEclipseVisibilityMask(b, "transit-not-c1-c4-mask", frame, "transit-sun-c1-shape", "transit-sun-c4-shape")
writeLunarEclipseVisibilityMask(b, "transit-not-greatest-mask", frame, "transit-sun-greatest-shape")
writeLunarEclipseVisibilityMask(b, "transit-not-c4-mask", frame, "transit-sun-c4-shape")
writeLunarEclipseVisibilityMask(b, "transit-not-c1-mask", frame, "transit-sun-c1-shape")
}
const (
transitMapColorEntire = "#5e846d"
transitMapColorSunrise = "#4e9da0"
transitMapColorSunset = "#e2aa4b"
transitMapColorNone = "#747b7d"
transitMapColorC1 = "#a3392f"
transitMapColorC2 = "#c0702a"
transitMapColorC3 = "#7a4ca0"
transitMapColorC4 = "#2f5ea3"
)
// writeTransitMapRegions 着色四类可见区：全程可见、日出时凌日已开始、日落时凌日未结束、不可见。
// 只有凌甚前后太阳在地平上的极区透镜与两端可见、凌甚不可见的高纬带都归入日落带，同月食可见图。
func writeTransitMapRegions(b *strings.Builder, frame svgmap.Frame, contacts transitMapContacts) {
_, startBoundary := transitMapSunUpPath(contacts.start, frame)
_, endBoundary := transitMapSunUpPath(contacts.end, frame)
fmt.Fprintf(b, `<g class="transit-visibility-regions" data-source="%s" clip-path="url(#transit-map-clip)">`, eclipseMapSourceTransitVisibilityRegions)
if frame.IsPolar() {
fmt.Fprintf(b, `<circle class="transit-not-visible-region" mask="url(#transit-not-visible-mask)" cx="%.3f" cy="%.3f" r="%.3f" fill="%s" fill-opacity="0.34"/>`,
frame.X+frame.Width/2, frame.Y+frame.Height/2, frame.Width/2, transitMapColorNone)
} else {
fmt.Fprintf(b, `<rect class="transit-not-visible-region" mask="url(#transit-not-visible-mask)" x="%.3f" y="%.3f" width="%.3f" height="%.3f" fill="%s" fill-opacity="0.34"/>`,
frame.X, frame.Y, frame.Width, frame.Height, transitMapColorNone)
}
fmt.Fprintf(b, `<use class="transit-sunset-region" mask="url(#transit-not-c4-mask)" href="#transit-sun-c1-shape" fill="%s" fill-opacity="0.34"/>`, transitMapColorSunset)
fmt.Fprintf(b, `<use class="transit-sunrise-region" mask="url(#transit-not-c1-mask)" href="#transit-sun-c4-shape" fill="%s" fill-opacity="0.34"/>`, transitMapColorSunrise)
fmt.Fprintf(b, `<g clip-path="url(#transit-sun-c4)"><g clip-path="url(#transit-sun-greatest)"><use class="transit-entire-region" href="#transit-sun-c1-shape" fill="%s" fill-opacity="0.34"/></g></g>`, transitMapColorEntire)
fmt.Fprintf(b, `<g clip-path="url(#transit-sun-c4)"><g mask="url(#transit-not-greatest-mask)"><use class="transit-sunset-region" href="#transit-sun-c1-shape" fill="%s" fill-opacity="0.34"/></g></g>`, transitMapColorSunset)
fmt.Fprintf(b, `<g mask="url(#transit-not-c1-c4-mask)"><use class="transit-sunset-region" href="#transit-sun-greatest-shape" fill="%s" fill-opacity="0.34"/></g>`, transitMapColorSunset)
b.WriteString(`</g>`)
writeEclipseMapGeoLine(b, frame, startBoundary, "c1-horizon", "#a56c16", 1.2, "4 3", "transit-map-clip", eclipseMapSourceTransitHorizonBoundaries)
writeEclipseMapGeoLine(b, frame, endBoundary, "c4-horizon", "#197a82", 1.2, "4 3", "transit-map-clip", eclipseMapSourceTransitHorizonBoundaries)
}
// writeTransitMapIsochrones 画选中接触的站心等时线：每条线是同一时刻看到该接触的地点，只保留该时刻太阳在视地平上的部分。
// 每隔若干条标一次时刻，标签按 LabelTable 避让。
func writeTransitMapIsochrones(b *strings.Builder, frame svgmap.Frame, transit basic.PlanetTransitResult, options TransitMapSVGOptions) {
table := &svgchart.LabelTable{}
format := "15:04"
if options.IsochroneStep%time.Minute != 0 {
format = "15:04:05"
}
for _, contact := range []struct {
kind basic.PlanetTransitContactKind
class string
color string
flag TransitIsochrones
}{
{basic.PlanetTransitC1, "c1-isochrone", transitMapColorC1, TransitIsochroneC1},
{basic.PlanetTransitC2, "c2-isochrone", transitMapColorC2, TransitIsochroneC2},
{basic.PlanetTransitC3, "c3-isochrone", transitMapColorC3, TransitIsochroneC3},
{basic.PlanetTransitC4, "c4-isochrone", transitMapColorC4, TransitIsochroneC4},
} {
if options.Isochrones&contact.flag == 0 {
continue
}
lines := basic.PlanetTransitContactIsochrones(transit, contact.kind, options.IsochroneStep)
labelEvery := transitMapIsochroneLabelEvery(len(lines))
for index, line := range lines {
segments := make([][]svgmap.GeoPoint, 0, len(line.Segments))
for _, segment := range line.Segments {
points := make([]svgmap.GeoPoint, len(segment))
for position, point := range segment {
points[position] = svgmap.GeoPoint{Longitude: point.Longitude, Latitude: point.Latitude}
}
segments = append(segments, points)
writeEclipseMapGeoLine(b, frame, points, contact.class, contact.color, 0.9, "none", "transit-map-clip", eclipseMapSourceTransitContactIsochrones)
}
if index%labelEvery != 0 {
continue
}
text := transitMapDisplayTime(basic.JD2DateByZone(line.JD, time.UTC, false), options).Format(format)
placement, ok := table.Place(text, 10, transitMapIsochroneLabelCandidates(segments, frame))
if !ok {
continue
}
fmt.Fprintf(b, `<text class="%s-label" x="%.3f" y="%.3f" fill="%s" stroke="#ffffff" stroke-width="2.6" paint-order="stroke" font-family="Arial, sans-serif" font-size="10" text-anchor="%s">%s</text>`,
contact.class, placement.X, placement.Y, contact.color, placement.Anchor, html.EscapeString(text))
}
}
}
// transitMapIsochroneLabelEvery 让每个接触最多标八条线。
func transitMapIsochroneLabelEvery(count int) int {
every := int(math.Ceil(float64(count) / 8))
if every < 1 {
every = 1
}
return every
}
// transitMapIsochroneLabelCandidates 从最长支路的中点向两端取画布内的候选位置。
func transitMapIsochroneLabelCandidates(segments [][]svgmap.GeoPoint, frame svgmap.Frame) []svgchart.LabelPlacement {
longest := -1
for index, segment := range segments {
if longest < 0 || len(segment) > len(segments[longest]) {
longest = index
}
}
if longest < 0 {
return nil
}
segment := segments[longest]
middle := len(segment) / 2
candidates := make([]svgchart.LabelPlacement, 0, 32)
for offset := 0; offset <= middle && len(candidates) < 32; offset++ {
for _, index := range []int{middle + offset, middle - offset} {
if index < 0 || index >= len(segment) || (offset == 0 && index != middle) {
continue
}
x, y, visible := frame.Project(segment[index].Longitude, segment[index].Latitude)
if !visible || x < frame.X+24 || x > frame.X+frame.Width-24 || y < frame.Y+14 || y > frame.Y+frame.Height-6 {
continue
}
candidates = append(candidates, svgchart.LabelPlacement{X: x, Y: y - 4, Anchor: "middle"})
}
}
return candidates
}
func writeTransitMapSummary(b *strings.Builder, transit basic.PlanetTransitResult, contacts transitMapContacts, options TransitMapSVGOptions) {
clock := func(value time.Time) string { return transitMapDisplayTime(value, options).Format("15:04:05") }
zone, _ := transitMapDisplayTime(contacts.greatest, options).Zone()
if zone == "" {
zone = "UTC"
}
if options.TimeScale == astro.TimeScaleUT1 {
zone = "UT1"
}
greatest, separation := "凌甚", "最小角距"
if options.Language == "en" {
greatest, separation = "Greatest", "least separation"
}
parts := []string{"C1 " + clock(contacts.start)}
if contacts.hasInternal {
parts = append(parts, "C2 "+clock(contacts.internalStart))
}
parts = append(parts, greatest+" "+clock(contacts.greatest))
if contacts.hasInternal {
parts = append(parts, "C3 "+clock(contacts.internalEnd))
}
parts = append(parts, "C4 "+clock(contacts.end))
line := fmt.Sprintf("%s (%s)", strings.Join(parts, " | "), zone)
fmt.Fprintf(b, `<text x="%.3f" y="82" fill="#293235" font-family="Arial, sans-serif" font-size="13" text-anchor="middle">%s</text>`,
float64(options.Width)/2, html.EscapeString(svgchart.EllipsizeText(line, float64(options.Width)-60, 13)))
note := fmt.Sprintf("%s %.1f″ | 太阳视半径 %.1f″ | 行星视半径 %.2f″（地心）", separation,
transit.MinimumSeparationArcsec, transit.SunSemidiameterArcsec, transit.PlanetSemidiameterArcsec)
if options.Language == "en" {
note = fmt.Sprintf("%s %.1f″ | solar semidiameter %.1f″ | planet semidiameter %.2f″ (geocentric)", separation,
transit.MinimumSeparationArcsec, transit.SunSemidiameterArcsec, transit.PlanetSemidiameterArcsec)
}
fmt.Fprintf(b, `<text x="%.3f" y="100" fill="#293235" font-family="Arial, sans-serif" font-size="13" text-anchor="middle">%s</text>`,
float64(options.Width)/2, html.EscapeString(note))
}
// writeTransitMapLegend 画区域色块与等时线图例，按画布宽度折行，返回行数。
func writeTransitMapLegend(b *strings.Builder, frame svgmap.Frame, canvasWidth float64, options TransitMapSVGOptions) int {
type entry struct {
text, color string
line bool
}
labels := []string{"全程可见", "日出时已在凌日", "日落时仍在凌日", "不可见", "一触等时线", "二触等时线", "三触等时线", "四触等时线"}
if options.Language == "en" {
labels = []string{"Entire transit", "Transit at sunrise", "Transit at sunset", "Not visible",
"C1 isochrones", "C2 isochrones", "C3 isochrones", "C4 isochrones"}
}
entries := []entry{
{labels[0], transitMapColorEntire, false}, {labels[1], transitMapColorSunrise, false},
{labels[2], transitMapColorSunset, false}, {labels[3], transitMapColorNone, false},
}
for index, item := range []struct {
flag TransitIsochrones
color string
}{
{TransitIsochroneC1, transitMapColorC1}, {TransitIsochroneC2, transitMapColorC2},
{TransitIsochroneC3, transitMapColorC3}, {TransitIsochroneC4, transitMapColorC4},
} {
if options.Isochrones&item.flag != 0 {
entries = append(entries, entry{labels[4+index], item.color, true})
}
}
width := func(item entry) float64 {
return lunarEclipseDetailedMapLegendIconWidth + svgchart.EstimatedTextWidth(item.text, lunarEclipseDetailedMapLegendFontSize)
}
available := canvasWidth - 2*lunarEclipseDetailedPageInset
var rows [][]entry
used := 0.0
for _, item := range entries {
if len(rows) == 0 || used+lunarEclipseDetailedMapLegendGap+width(item) > available {
rows = append(rows, nil)
used = -lunarEclipseDetailedMapLegendGap
}
rows[len(rows)-1] = append(rows[len(rows)-1], item)
used += lunarEclipseDetailedMapLegendGap + width(item)
}
baseY := frame.Y + frame.Height + 31
for rowIndex, row := range rows {
total := -lunarEclipseDetailedMapLegendGap
for _, item := range row {
total += lunarEclipseDetailedMapLegendGap + width(item)
}
x := math.Max(lunarEclipseDetailedPageInset, frame.X+frame.Width/2-total/2)
y := baseY + float64(rowIndex)*lunarEclipseDetailedMapLegendLineStep
for _, item := range row {
if item.line {
fmt.Fprintf(b, `<line x1="%.3f" y1="%.3f" x2="%.3f" y2="%.3f" stroke="%s" stroke-width="1.4"/>`, x, y-4, x+18, y-4, item.color)
} else {
fmt.Fprintf(b, `<rect x="%.3f" y="%.3f" width="18" height="9" fill="%s" fill-opacity="0.78"/>`, x, y-8, item.color)
}
fmt.Fprintf(b, `<text x="%.3f" y="%.3f" fill="#465053" font-family="Arial, sans-serif" font-size="%.0f">%s</text>`,
x+lunarEclipseDetailedMapLegendIconWidth, y, lunarEclipseDetailedMapLegendFontSize, html.EscapeString(item.text))
x += width(item) + lunarEclipseDetailedMapLegendGap
}
}
return len(rows)
}
func writeTransitMapFooter(
b *strings.Builder,
frame svgmap.Frame,
options TransitMapSVGOptions,
projection svgmap.Projection,
instant time.Time,
legendRows int,
) {
text := options.FooterNote
if text == "" {
if options.Language == "en" {
text = eclipseMapProjectionLabel(projection, "en") + "; regions follow whether the Sun's centre is above the apparent horizon (standard refraction) at C1, greatest and C4"
if options.Isochrones != 0 {
text += "; isochrones are topocentric contact times"
}
text += "."
} else {
text = eclipseMapProjectionLabel(projection, "zh") + "；按一触、凌甚、四触太阳中心是否在视地平上分区（计入标准大气折射）"
if options.Isochrones != 0 {
text += "；等时线为站心接触时刻"
}
text += "。"
}
}
const footerBottomPadding = 26.0
// 页脚紧跟图例末行，不与图例重叠；行数按画布底边截断，时标声明独占最后一行。
baseline := frame.Y + frame.Height + 31 + float64(legendRows-1)*lunarEclipseDetailedMapLegendLineStep + 18
maxWidth := float64(options.Width) - frame.X - 24
lines := svgchart.WrapText(text, maxWidth, 11)
lines = svgchart.FooterLinesWithScale(lines, timenote.Scale(options.TimeScale, instant, options.Location, options.Language), maxWidth, 11,
svgchart.BaselineLineLimit(11, svgchart.FooterLineHeight(11), baseline, float64(options.Height)-footerBottomPadding))
for index, line := range lines {
fmt.Fprintf(b, `<text x="%.3f" y="%.3f" fill="#596164" font-family="Georgia, 'Times New Roman', serif" font-size="11">%s</text>`,
frame.X, baseline+float64(index)*svgchart.FooterLineHeight(11), html.EscapeString(line))
}
}
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