[feat](trx-frontend-http): draw APRS symbols from the sprite sheets

Resolve a table/code pair to a sprite cell in aprs-shared, and use it
from both the packet lists and the map markers, which had each been
printing the raw symbol character in a bordered box.

A table identifier of / or \ selects the primary or alternate sheet
directly.  Anything else is an overlay character, which the APRS spec
draws on top of the alternate symbol -- so those stack the overlay sheet
over the alternate one rather than picking a sheet.  Codes outside
0x21..0x7E have no cell and keep the old character box.

The sheet URLs stay in the stylesheet so a min-resolution query can swap
in the retina sheets; only the cell offset is computed and set inline.
Map markers share the helper through the plugin chunk, so the map stays
free of any remote symbol fetch.

Verified in a browser against the real stylesheet and sheets: /> is a
car, /_ a WX circle, /& an igate diamond, \n a red triangle, and the
overlays S> and 7# carry their character on the alternate symbol.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018huL1ELyr86yVqfAabtioA
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/frontend/src/map-core.ts

@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 import type * as Leaflet from "leaflet";
+import { aprsSymbolSprite } from "./plugins/aprs-shared";
 
 export {};
 
@@ -2002,10 +2003,15 @@ const mapWindow = window as unknown as MapWindow;
 
   function aprsSymbolIcon(symbolTable: string, symbolCode: string): Leaflet.DivIcon | null {
     if (!symbolTable || !symbolCode) return null;
-    const table = symbolTable === "/" ? "primary" : "alternate";
+    const sprite = aprsSymbolSprite(symbolTable, symbolCode);
+    const html = sprite
+      ? `<div class="aprs-symbol aprs-symbol-marker ${sprite.className}" role="img"` +
+        ` style="background-position:${sprite.backgroundPosition}"` +
+        ` title="${escapeMapHtml(sprite.label)}" aria-label="${escapeMapHtml(sprite.label)}"></div>`
+      : `<div class="aprs-symbol aprs-symbol-marker aprs-symbol-local" title="${symbolTable === "/" ? "primary" : "alternate"} APRS symbol ${escapeMapHtml(symbolCode)}">${escapeMapHtml(symbolCode)}</div>`;
     return L.divIcon({
       className: "",
-      html: `<div class="aprs-symbol-local" title="${table} APRS symbol ${escapeMapHtml(symbolCode)}">${escapeMapHtml(symbolCode)}</div>`,
+      html,
       iconSize: [24, 24],
       iconAnchor: [12, 12],
       popupAnchor: [0, -12]

src/trx-client/trx-frontend/trx-frontend-http/frontend/src/plugins/aprs-shared.ts

@@ -108,8 +108,80 @@ function escapeAprsCharacter(character: string): string {
   return character;
 }
 
+// The vendored sprite sheets (assets/web/vendor/aprs-symbols-24-*.png) are
+// 16x6 grids of 24px cells covering the printable codes 0x21..0x7E, so a
+// symbol's cell index is simply `code - 0x21`.  The sheet URLs live in CSS so
+// the retina variants can be picked up by a media query; only the cell offsets
+// are computed here.
+const APRS_SPRITE_COLUMNS = 16;
+const APRS_SPRITE_CELL_PX = 24;
+const APRS_SPRITE_FIRST_CODE = 0x21;
+const APRS_SPRITE_LAST_CODE = 0x7e;
+
+export interface AprsSymbolSprite {
+  /** Sheet modifier class appended to `.aprs-symbol`. */
+  className: string;
+  /** `background-position` covering the overlay layer first, if any. */
+  backgroundPosition: string;
+  /** Human-readable description for the tooltip. */
+  label: string;
+}
+
+function aprsSpriteOffset(code: string): string | null {
+  if (code.length !== 1) return null;
+  const point = code.charCodeAt(0);
+  if (point < APRS_SPRITE_FIRST_CODE || point > APRS_SPRITE_LAST_CODE) return null;
+  const index = point - APRS_SPRITE_FIRST_CODE;
+  const column = index % APRS_SPRITE_COLUMNS;
+  const row = Math.floor(index / APRS_SPRITE_COLUMNS);
+  return `${String(-column * APRS_SPRITE_CELL_PX)}px ${String(-row * APRS_SPRITE_CELL_PX)}px`;
+}
+
+/**
+ * Resolve an APRS table/code pair to a sprite cell.  A table identifier of `/`
+ * selects the primary sheet and `\` the alternate one; any other character is
+ * an overlay, which draws that character from the overlay sheet on top of the
+ * alternate symbol.  Returns null when the pair is outside the sprite sheets,
+ * leaving callers to fall back to the raw character.
+ */
+export function aprsSymbolSprite(
+  symbolTable: string | null | undefined,
+  symbolCode: string | null | undefined,
+): AprsSymbolSprite | null {
+  if (!symbolTable || !symbolCode) return null;
+  const symbolOffset = aprsSpriteOffset(symbolCode);
+  if (!symbolOffset) return null;
+  if (symbolTable === "/") {
+    return {
+      className: "aprs-symbol-primary",
+      backgroundPosition: symbolOffset,
+      label: `Primary APRS symbol ${symbolTable}${symbolCode}`,
+    };
+  }
+  if (symbolTable === "\\") {
+    return {
+      className: "aprs-symbol-alternate",
+      backgroundPosition: symbolOffset,
+      label: `Alternate APRS symbol ${symbolTable}${symbolCode}`,
+    };
+  }
+  const overlayOffset = aprsSpriteOffset(symbolTable);
+  if (!overlayOffset) return null;
+  return {
+    className: "aprs-symbol-overlaid",
+    backgroundPosition: `${overlayOffset}, ${symbolOffset}`,
+    label: `Alternate APRS symbol \\${symbolCode} with overlay ${symbolTable}`,
+  };
+}
+
 export function renderLocalAprsSymbol(packet: AprsPacket, escapeHtml: (value: string) => string): string {
   if (!packet.symbolTable || !packet.symbolCode) return "";
+  const sprite = aprsSymbolSprite(packet.symbolTable, packet.symbolCode);
+  if (sprite) {
+    return `<span class="aprs-symbol ${sprite.className}" role="img"` +
+      ` style="background-position:${sprite.backgroundPosition}"` +
+      ` title="${escapeHtml(sprite.label)}" aria-label="${escapeHtml(sprite.label)}"></span>`;
+  }
   const symbol = escapeHtml(packet.symbolCode);
   const table = packet.symbolTable === "/" ? "Primary" : "Alternate";
   return `<span class="aprs-symbol aprs-symbol-local" title="${table} APRS symbol ${symbol}">${symbol}</span>`;

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/aprs-symbols.test.mjs

@@ -0,0 +1,85 @@
+// SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+import assert from "node:assert/strict";
+import test from "node:test";
+import vm from "node:vm";
+import { readFile } from "node:fs/promises";
+import { bundleEntry } from "./bundle-entry.mjs";
+
+const sharedUrl = new URL("../src/plugins/aprs-shared.ts", import.meta.url);
+const stylePath = new URL("../../assets/web/style.css", import.meta.url);
+
+async function loadShared() {
+  const source = await bundleEntry(sharedUrl, "trxAprsShared");
+  const context = vm.createContext({ Math, String, Number, Array, Date, Set, console });
+  new vm.Script(source).runInContext(context);
+  return context.trxAprsShared;
+}
+
+// The sheets are 16x6 grids of 24px cells covering 0x21..0x7E, so cell index
+// is `code - 0x21`.  Getting this wrong shifts every station to a neighbouring
+// icon, which is invisible in a screenshot but wrong on every packet.
+test("sprite cells are indexed from the first printable symbol code", async () => {
+  const { aprsSymbolSprite } = await loadShared();
+
+  const first = aprsSymbolSprite("/", "!");
+  assert.equal(first.className, "aprs-symbol-primary");
+  assert.equal(first.backgroundPosition, "0px 0px");
+  assert.equal(first.label, "Primary APRS symbol /!");
+  // '>' is 0x3E -> index 29 -> column 13, row 1.
+  assert.equal(aprsSymbolSprite("/", ">").backgroundPosition, "-312px -24px");
+  // '~' is 0x7E -> index 93 -> the last cell of the last row.
+  assert.equal(aprsSymbolSprite("/", "~").backgroundPosition, "-312px -120px");
+});
+
+test("the table identifier selects the primary, alternate, or overlay sheet", async () => {
+  const { aprsSymbolSprite } = await loadShared();
+
+  assert.equal(aprsSymbolSprite("/", "_").className, "aprs-symbol-primary");
+  assert.equal(aprsSymbolSprite("\\", "_").className, "aprs-symbol-alternate");
+
+  // An alphanumeric table identifier is an overlay character drawn on top of
+  // the alternate symbol: overlay cell first, then the symbol cell.
+  const overlaid = aprsSymbolSprite("S", ">");
+  assert.equal(overlaid.className, "aprs-symbol-overlaid");
+  assert.equal(overlaid.backgroundPosition, "-48px -72px, -312px -24px");
+  assert.equal(overlaid.label, "Alternate APRS symbol \\> with overlay S");
+});
+
+test("codes outside the sprite sheets fall back to the raw character", async () => {
+  const { aprsSymbolSprite, renderLocalAprsSymbol } = await loadShared();
+  const escape = (value) => value;
+
+  assert.equal(aprsSymbolSprite("/", " "), null);
+  assert.equal(aprsSymbolSprite("/", ""), null);
+  assert.equal(aprsSymbolSprite("/", "ab"), null);
+  assert.equal(aprsSymbolSprite(null, ">"), null);
+
+  assert.equal(renderLocalAprsSymbol({ symbolTable: "/", symbolCode: " " }, escape),
+    '<span class="aprs-symbol aprs-symbol-local" title="Primary APRS symbol  "> </span>');
+  assert.equal(renderLocalAprsSymbol({}, escape), "");
+});
+
+test("rendered symbols carry a sprite class and an inline cell offset", async () => {
+  const { renderLocalAprsSymbol } = await loadShared();
+  const html = renderLocalAprsSymbol({ symbolTable: "/", symbolCode: ">" }, (value) => value);
+
+  assert.match(html, /class="aprs-symbol aprs-symbol-primary"/);
+  assert.match(html, /style="background-position:-312px -24px"/);
+  assert.match(html, /aria-label="Primary APRS symbol \/>"/);
+  assert.equal(html.includes("http"), false);
+});
+
+// The cell offsets are computed in the bundles, so the sheet URLs and the grid
+// geometry have to stay in lockstep with them here.
+test("the stylesheet serves every sheet locally at the sprite geometry", async () => {
+  const css = await readFile(stylePath, "utf8");
+
+  assert.match(css, /\.aprs-symbol\s*\{[^}]*background-size:\s*384px 144px/);
+  for (const sheet of ["24-0", "24-1", "24-2", "24-0-2x", "24-1-2x", "24-2-2x"]) {
+    assert.ok(css.includes(`url('/vendor/aprs-symbols-${sheet}.png')`), `missing sheet ${sheet}`);
+  }
+  assert.match(css, /\.aprs-symbol-overlaid\s*\{[^}]*aprs-symbols-24-2\.png'\), url\('\/vendor\/aprs-symbols-24-1\.png'\)/);
+});

src/trx-client/trx-frontend/trx-frontend-http/frontend/tests/bundle-entry.mjs

@@ -4,7 +4,7 @@
 
 import { build } from "esbuild";
 
-export async function bundleEntry(entryUrl) {
+export async function bundleEntry(entryUrl, globalName) {
   const result = await build({
     entryPoints: [entryUrl.pathname],
     bundle: true,
@@ -12,6 +12,7 @@ export async function bundleEntry(entryUrl) {
     platform: "browser",
     target: "es2022",
     write: false,
+    ...(globalName ? { globalName } : {}),
   });
   const output = result.outputFiles[0];
   if (!output) throw new Error(`No bundle output for ${entryUrl.pathname}`);