feat: Lua app firmware for the E32R40T display module

Boots to a launcher that lists /apps/<name>/main.lua on the SD card and runs
the selected app in a vendored Lua 5.4 with gui, input, fs, sys and log
bindings. Settings persist as a Lua table in /settings.lua, covering touch
calibration and screen rotation, with a settings app to edit both. Rotation is
applied after mapping raw touch into the panel's rotation-0 frame, so turning
the UI never invalidates a calibration.

src/main.cpp

@@ -0,0 +1,114 @@
+#include <SD.h>
+#include <SPI.h>
+#include <TFT_eSPI.h>
+#include <XPT2046_Touchscreen.h>
+
+#include "lua/lua_app.h"
+#include "settings.h"
+
+// SD card is on a separate bus from the display/touch (board schematic)
+static constexpr int SD_CS = 5;
+static constexpr int SD_SCK = 18;
+static constexpr int SD_MOSI = 23;
+static constexpr int SD_MISO = 19;
+static constexpr int TOUCH_CS = 33;
+
+TFT_eSPI tft;
+SPIClass touchSpi(HSPI);
+SPIClass& sdSpi = SPI;
+XPT2046_Touchscreen touch(TOUCH_CS);
+LuaApp app(tft, touch);
+
+bool sdOk = false;
+String appPath;
+
+void drawLauncher() {
+  tft.fillScreen(TFT_WHITE);
+  tft.setTextColor(TFT_BLACK, TFT_WHITE);
+  tft.drawString("esp32-lcd - tap an app", 10, 10);
+
+  File dir = SD.open("/apps");
+  int y = 40;
+  while (File entry = dir.openNextFile()) {
+    if (entry.isDirectory() && entry.name()[0] != '.') {
+      tft.drawRect(10, y - 4, tft.width() - 20, 28, TFT_BLACK);
+      tft.drawString(entry.name(), 18, y);
+      y += 36;
+    }
+    entry.close();
+  }
+  dir.close();
+}
+
+// ponytail: first N rows of 36px = first N app dirs, in SD order. A scrollable
+// menu widget can come later; this is a launcher, not an OS.
+void launcherTouch() {
+  if (!touch.touched()) return;
+  TS_Point p = touch.getPoint();
+  int16_t tx, ty;
+  LuaApp::mapTouch(tft, p, tx, ty);
+  int idx = (ty - 40) / 36;
+  if (idx < 0) return;
+
+  File dir = SD.open("/apps");
+  int i = 0;
+  while (File entry = dir.openNextFile()) {
+    if (entry.isDirectory() && entry.name()[0] != '.') {
+      if (i++ == idx) {
+        appPath = String("/apps/") + entry.name() + "/main.lua";
+        entry.close();
+        break;
+      }
+    }
+    entry.close();
+  }
+  dir.close();
+}
+
+void setup() {
+  Serial.begin(115200);
+  tft.begin();
+  tft.setRotation(0);
+  tft.fillScreen(TFT_WHITE);
+  touchSpi.begin(14, 12, 13, TOUCH_CS);
+  touch.begin(touchSpi);
+
+  sdSpi.begin(SD_SCK, SD_MISO, SD_MOSI, SD_CS);
+  if (!SD.begin(SD_CS, sdSpi)) {
+    tft.setTextColor(TFT_RED, TFT_WHITE);
+    tft.drawString("SD card mount failed", 10, 10);
+    Serial.println("SD mount failed");
+    return;
+  }
+  sdOk = true;
+  settings.load();  // absent file keeps the built-in touch defaults
+  tft.setRotation(settings.rotationIndex());
+  drawLauncher();
+  Serial.println("launcher ready");
+}
+
+void loop() {
+  if (!sdOk) return;  // SD failed to mount; error already drawn
+
+  if (app.running()) {
+    app.loop();
+    if (!app.running()) {
+      appPath = "";
+      tft.setRotation(settings.rotationIndex());  // apps may have rotated the frame
+      drawLauncher();
+      Serial.println("launcher ready");
+    }
+    return;
+  }
+
+  if (appPath.length() > 0) {
+    String path = appPath;
+    appPath = "";
+    Serial.printf("launching %s\n", path.c_str());
+    app.load(path.c_str());
+    return;
+  }
+
+  launcherTouch();
+  delay(10);
+}