package main import ( "math/rand" "strconv" "sync" "time" "github.com/ryanhamamura/via" "github.com/ryanhamamura/via/h" "github.com/ryanhamamura/via/maplibre" ) type posMsg struct { Lng float64 `json:"lng"` Lat float64 `json:"lat"` } var ( vehicleOnce sync.Once vehicle struct { mu sync.RWMutex lng, lat float64 } ) func main() { v := via.New() v.Config(via.Options{ DocumentTitle: "MapLibre GL Example", ServerAddress: ":7331", DevMode: true, Plugins: []via.Plugin{maplibre.Plugin}, }) // Single goroutine moves the vehicle — all clients read the same position. vehicle.lng = -122.43 vehicle.lat = 37.77 vehicleOnce.Do(func() { go func() { for { time.Sleep(time.Second) vehicle.mu.Lock() vehicle.lng = -122.43 + (rand.Float64()-0.5)*0.02 vehicle.lat = 37.77 + (rand.Float64()-0.5)*0.02 vehicle.mu.Unlock() } }() }) v.Page("/", func(c *via.Context) { m := maplibre.New(c, maplibre.Options{ Style: "https://demotiles.maplibre.org/style.json", Center: maplibre.LngLat{Lng: -122.4194, Lat: 37.7749}, Zoom: 10, Height: "500px", }) m.AddControl("nav", maplibre.NavigationControl{}) m.AddControl("scale", maplibre.ScaleControl{Unit: "metric"}) // Static markers with popups m.AddMarker("sf", maplibre.Marker{ LngLat: maplibre.LngLat{Lng: -122.4194, Lat: 37.7749}, Color: "#e74c3c", Popup: &maplibre.Popup{ Content: "San Francisco
The Golden City
", }, }) m.AddMarker("oak", maplibre.Marker{ LngLat: maplibre.LngLat{Lng: -122.2711, Lat: 37.8044}, Color: "#2ecc71", Popup: &maplibre.Popup{ Content: "Oakland", }, }) // Custom SVG ship marker (static) m.AddMarker("ship", maplibre.Marker{ LngLat: maplibre.LngLat{Lng: -122.38, Lat: 37.80}, Element: ``, Anchor: "center", Rotation: 45, Popup: &maplibre.Popup{ Content: "FerryHeading NE
", }, }) // Custom SVG vehicle marker — reads shared Go state vehicleLng := c.Signal(-122.43) vehicleLat := c.Signal(37.77) m.AddMarker("vehicle", maplibre.Marker{ LngSignal: vehicleLng, LatSignal: vehicleLat, Element: ``, Anchor: "center", }) c.OnInterval(time.Second, func() { vehicle.mu.RLock() lng, lat := vehicle.lng, vehicle.lat vehicle.mu.RUnlock() vehicleLng.SetValue(lng) vehicleLat.SetValue(lat) c.SyncSignals() }) // Yellow click marker — synced across clients via PubSub clickLng := c.Signal(-122.4194) clickLat := c.Signal(37.7749) m.AddMarker("clicked", maplibre.Marker{ LngSignal: clickLng, LatSignal: clickLat, Color: "#f39c12", }) via.Subscribe(c, "map.click", func(msg posMsg) { clickLng.SetValue(msg.Lng) clickLat.SetValue(msg.Lat) c.SyncSignals() }) click := m.OnClick() handleClick := c.Action(func() { e := click.Data() via.Publish(c, "map.click", posMsg{Lng: e.LngLat.Lng, Lat: e.LngLat.Lat}) }) // Blue draggable pin — synced across clients via PubSub pinLng := c.Signal(-122.41) pinLat := c.Signal(37.78) m.AddMarker("pin", maplibre.Marker{ LngSignal: pinLng, LatSignal: pinLat, Color: "#3498db", Draggable: true, }) via.Subscribe(c, "map.pin", func(msg posMsg) { pinLng.SetValue(msg.Lng) pinLat.SetValue(msg.Lat) c.SyncSignals() }) handlePinDrag := c.Action(func() { lng, _ := strconv.ParseFloat(pinLng.String(), 64) lat, _ := strconv.ParseFloat(pinLat.String(), 64) via.Publish(c, "map.pin", posMsg{Lng: lng, Lat: lat}) }) // GeoJSON polygon source + fill layer m.AddSource("park", maplibre.GeoJSONSource{ Data: map[string]any{ "type": "Feature", "geometry": map[string]any{ "type": "Polygon", "coordinates": []any{[]any{ []float64{-122.4547, 37.7654}, []float64{-122.4547, 37.7754}, []float64{-122.4387, 37.7754}, []float64{-122.4387, 37.7654}, []float64{-122.4547, 37.7654}, }}, }, "properties": map[string]any{ "name": "Golden Gate Park", }, }, }) m.AddLayer(maplibre.Layer{ ID: "park-fill", Type: "fill", Source: "park", Paint: map[string]any{ "fill-color": "#2ecc71", "fill-opacity": 0.3, }, }) // FlyTo actions zoom14 := 14.0 flyToSF := c.Action(func() { m.FlyTo(maplibre.CameraOptions{ Center: &maplibre.LngLat{Lng: -122.4194, Lat: 37.7749}, Zoom: &zoom14, }) }) flyToOak := c.Action(func() { m.FlyTo(maplibre.CameraOptions{ Center: &maplibre.LngLat{Lng: -122.2711, Lat: 37.8044}, Zoom: &zoom14, }) }) c.View(func() h.H { return h.Div( h.Div( h.Attr("style", "max-width:960px;margin:0 auto;padding:1rem;font-family:sans-serif"), h.H1(h.Text("MapLibre GL Example")), m.Element( click.Input(handleClick.OnInput()), h.Input(h.Type("hidden"), pinLng.Bind(), handlePinDrag.OnInput()), ), h.Div(h.Attr("style", "margin-top:1rem;display:flex;gap:0.5rem;flex-wrap:wrap"), h.Button(h.Text("Fly to San Francisco"), flyToSF.OnClick()), h.Button(h.Text("Fly to Oakland"), flyToOak.OnClick()), ), h.Div(h.Attr("style", "margin-top:0.5rem;font-size:0.9rem"), h.P(h.Text("Zoom: "), m.Zoom.Text()), h.P(h.Text("Center: "), m.CenterLng.Text(), h.Text(", "), m.CenterLat.Text()), h.P(h.Text("Click: "), clickLng.Text(), h.Text(", "), clickLat.Text()), h.P(h.Text("Vehicle: "), vehicleLng.Text(), h.Text(", "), vehicleLat.Text()), h.P(h.Text("Draggable Pin: "), pinLng.Text(), h.Text(", "), pinLat.Text()), ), ), ) }) }) v.Start() }