feat(ui): add a home button to the status bar, rename launcher to home

Leaving an app was the app's own responsibility, so one that shipped without
an exit could only be escaped with a reset. The bar now paints a back button
into its leading square and the firmware treats that rect as home, acting on
release so a press sliding into the app cancels. The app it returns to is
/apps/home, which is what it is to the user.

Card grids in home and settings centre left to right as a unit.

src/lua/bindings/sys.cpp

@@ -141,7 +141,7 @@ void registerSys(lua_State* L) {
       // --- Blocks for the given time.
       // @param ms integer
       {"delay", l_sys_delay},
-      // --- Ends this app and returns to the launcher.
+      // --- Ends this app and returns home.
       {"exit", l_sys_exit},
       // --- Directory name of the running app, for example "settings".
       // @return string

src/lua/lua_app.cpp

@@ -101,12 +101,14 @@ bool LuaApp::takeFailure() {
   return value;
 }
 
-bool LuaApp::load(const char* path) {
+bool LuaApp::load(const char* path, bool isHome) {
   closeState();
+  this->isHome = isHome;
+  homeArmed = false;
   // Cleared per app: the interval outlives the app that set it, so a ticking app
   // followed by one that never ticks would keep calling a nil global.
   tickIntervalMs = 0;
-  // The launcher tap may still be down; swallow that gesture's release.
+  // The tap that launched this app may still be down; swallow that gesture's release.
   lastTouched = true;
   ignoreRelease = true;
   state = luaL_newstate();
@@ -177,8 +179,9 @@ void LuaApp::drawStatusBar() {
   lua_getglobal(state, "__statusbar");
   lua_getfield(state, -1, "draw");
   lua_remove(state, -2);
+  lua_pushboolean(state, !isHome);  // whether to paint the home button
   tft.resetViewport();  // the bar paints in panel coordinates, the app does not
-  if (lua_pcall(state, 0, 0, 0) != LUA_OK) {
+  if (lua_pcall(state, 1, 0, 0) != LUA_OK) {
     Serial.printf("[statusbar] %s\n", luaL_tolstring(state, -1, nullptr));
     lua_pop(state, 2);
     barBroken = true;
@@ -229,7 +232,19 @@ void LuaApp::loop() {
   if (touched) {
     TS_Point p = touch.getPoint();
     mapTouch(p, lastX, lastY);
-    if (lastY < 0) touched = false;  // the bar is the host's, and it takes no input yet
+  }
+
+  // The bar is the host's: apps never see a touch in it, and its one control acts on
+  // release, so a press that slides off into the app cancels like any other button.
+  if (touched && lastY < 0) {
+    homeArmed = homeArmed || inHomeButton();
+    touched = false;
+  } else if (homeArmed) {
+    homeArmed = false;
+    if (lastY < 0) {
+      requestExit();
+      return;
+    }
   }
   if (touched && !lastTouched) {
     fireTouch("on_touch_down", lastX, lastY);

src/lua/lua_app.h

@@ -15,10 +15,11 @@ class LuaApp {
   LuaApp(TFT_eSPI& tft, XPT2046_Touchscreen& touch);
   ~LuaApp();
 
-  bool load(const char* path);
+  // `isHome` marks the app the host falls back to, which needs no way back to itself.
+  bool load(const char* path, bool isHome = false);
   void loop();
 
-  // Directory name of the running app ("launcher"), for the status bar.
+  // Directory name of the running app ("settings"), for the status bar.
   const String& name() const { return appName; }
 
   // Lets an app own the whole panel: no viewport, no status bar. The touch calibration
@@ -64,6 +65,8 @@ class LuaApp {
   bool lastTouched = false;
   bool ignoreRelease = false;
   bool fullscreen = false;
+  bool isHome = false;
+  bool homeArmed = false;
   String appName;
   // One strike: a bar that failed once fails identically every second, and the serial
   // log is the only place anyone would see it.
@@ -92,6 +95,12 @@ class LuaApp {
   // and the touch offset.
   int16_t barInset() const { return (fullscreen || barBroken) ? 0 : barHeight; }
 
+  // The home button is the leading square of the bar, which is what /lib/statusbar.lua
+  // paints into. Touches are in app space, so the bar is above y = 0.
+  bool inHomeButton() const {
+    return !isHome && lastY < 0 && lastY >= -barInset() && lastX >= 0 && lastX < barInset();
+  }
+
   void registerBindings();
   bool callGlobal(const char* name, int nargs = 0);
   bool hasGlobal(const char* name);

src/main.cpp

@@ -16,7 +16,7 @@ static constexpr int SD_MOSI = 23;
 static constexpr int SD_MISO = 19;
 static constexpr int TOUCH_CS = 33;
 
-static const char* LAUNCHER = "/apps/launcher/main.lua";
+static const char* HOME = "/apps/home/main.lua";
 static constexpr uint32_t ERROR_HOLD_MS = 5000;
 
 // Arduino's default 8KB loop stack is not enough once a TLS handshake runs inside a
@@ -42,7 +42,7 @@ void fallbackScreen(const char* message) {
   tft.setTextColor(TFT_RED, TFT_WHITE);
   tft.drawString(message, 10, 10);
   tft.setTextColor(TFT_BLACK, TFT_WHITE);
-  tft.drawString("expected /apps/launcher/main.lua", 10, 30);
+  tft.drawString("expected /apps/home/main.lua", 10, 30);
   Serial.printf("halted: %s\n", message);
   halted = true;
 }
@@ -52,8 +52,8 @@ void startApp(const String& path) {
   tft.setRotation(settings.rotationIndex());  // apps may have rotated the frame
   statusbar::apply(tft, 0);
   Serial.printf("launching %s\n", path.c_str());
-  if (app.load(path.c_str())) return;
-  if (path == LAUNCHER) fallbackScreen("launcher failed to start");
+  if (app.load(path.c_str(), path == HOME)) return;
+  if (path == HOME) fallbackScreen("home failed to start");
 }
 
 void setup() {
@@ -71,7 +71,7 @@ void setup() {
   }
   settings.load();  // absent file keeps the built-in defaults
   net::begin();
-  startApp(LAUNCHER);
+  startApp(HOME);
 }
 
 void loop() {
@@ -86,11 +86,11 @@ void loop() {
     app.loop();
     if (!app.running()) nextApp = app.takePendingLaunch();
   } else {
-    // An app that died left its message on screen, and the launcher is about to paint
-    // over it. Serial alone is no help to anyone holding the device.
+    // An app that died left its message on screen, and home is about to paint over it.
+    // Serial alone is no help to anyone holding the device.
     if (app.takeFailure()) delay(ERROR_HOLD_MS);
 
-    String path = nextApp.length() > 0 ? nextApp : String(LAUNCHER);
+    String path = nextApp.length() > 0 ? nextApp : String(HOME);
     nextApp = "";
     startApp(path);
   }