Optimize map performance: reduce payload 75%, faster rendering

- Remove factors from heatmap scores, fetch on-demand via point_detail
- Pre-encode initial scores JSON once instead of per-render
- Don't store scores in socket assigns (reduce memory)
- Pre-calculate RGBA color lookup table for canvas rendering
- Batch fillStyle changes, hoist math out of inner loop
- Show topbar immediately on data requests (no 300ms delay)

assets/js/propagation_map_hook.js

@@ -264,14 +264,21 @@ export const PropagationMap = {
       }
     })
 
-    // Click on map to show factor breakdown + range circle
+    // Click on map to request factor detail from server
     this.map.on("click", (e) => {
-      const detail = this.lookupPoint(e.latlng.lat, e.latlng.lng)
+      const basic = this.lookupPoint(e.latlng.lat, e.latlng.lng)
+      if (basic) {
+        this.showRangeCircles(basic)
+        this.pushEvent("point_detail", { lat: e.latlng.lat, lon: e.latlng.lng })
+      }
+    })
+
+    this.handleEvent("point_detail", (detail) => {
       if (detail) {
-        this.showRangeCircles(detail)
+        const merged = { ...detail, ...this.bandInfo }
         this.detailPopup
           .setLatLng([detail.lat, detail.lon])
-          .setContent(buildPopupHTML(detail))
+          .setContent(buildPopupHTML(merged))
           .openOn(this.map)
       }
     })
@@ -327,6 +334,13 @@ export const PropagationMap = {
       this.gridData.set(key, s)
     })
 
+    // Pre-calculate RGBA strings for scores 0-100
+    const colorCache = new Array(101)
+    for (let i = 0; i <= 100; i++) {
+      const c = this.scoreColorRGB(i)
+      colorCache[i] = `rgba(${c.r},${c.g},${c.b},0.55)`
+    }
+
     const self = this
     this.scoreOverlay = L.GridLayer.extend({
       createTile(coords) {
@@ -345,15 +359,20 @@ export const PropagationMap = {
         const lonPerPx = (se.lng - nw.lng) / size.x
         const cellPxX = Math.max(1, Math.ceil(step / lonPerPx))
         const cellPxY = Math.max(1, Math.ceil(step / Math.abs(latPerPx)))
+        const absLatPerPx = Math.abs(latPerPx)
 
+        let lastColor = null
         for (let py = 0; py < size.y; py += cellPxY) {
+          const lat = nw.lat - py * absLatPerPx
           for (let px = 0; px < size.x; px += cellPxX) {
-            const lat = nw.lat - py * Math.abs(latPerPx)
             const lon = nw.lng + px * lonPerPx
             const score = self.interpolateScore(lat, lon, step)
             if (score !== null) {
-              const color = self.scoreColorRGB(score)
-              ctx.fillStyle = `rgba(${color.r},${color.g},${color.b},0.55)`
+              const color = colorCache[Math.max(0, Math.min(100, Math.round(score)))]
+              if (color !== lastColor) {
+                ctx.fillStyle = color
+                lastColor = color
+              }
               ctx.fillRect(px, py, cellPxX, cellPxY)
             }
           }

lib/microwaveprop_web/live/map_live.ex

@@ -60,6 +60,11 @@ defmodule MicrowavepropWeb.MapLive do
     {:noreply, socket}
   end
 
+  def handle_event("point_detail", %{"lat" => lat, "lon" => lon}, socket) do
+    detail = Propagation.point_detail(socket.assigns.selected_band, lat, lon)
+    {:noreply, push_event(socket, "point_detail", detail || %{})}
+  end
+
   def handle_event("map_bounds", bounds, socket) do
     scores = Propagation.latest_scores(socket.assigns.selected_band, bounds)
 
@@ -121,7 +126,7 @@ defmodule MicrowavepropWeb.MapLive do
         id="propagation-map"
         phx-hook="PropagationMap"
         phx-update="ignore"
-        data-scores={Jason.encode!(@scores)}
+        data-scores={@initial_scores_json}
         data-band-info={Jason.encode!(band_info(@selected_band))}
         class="absolute inset-0 z-0"
       >