examples/lvgldemo: optional second pointer device

The NuttX LVGL port can read two pointer devices into the same UI, and
the demo now exposes that: the physical touchscreen stays on the
primary path and EXAMPLES_LVGLDEMO_UTOUCH_DEVPATH names the second one
typically a VNC server's remote pointer. Pointing the single input
at the remote device had traded the panel's touch away for it.

Assisted-by: Claude:opus-5
Signed-off-by: Jorge Guzman <jorge.gzm@gmail.com>

Author: JorgeGzm

examples/lvgldemo/Kconfig

@@ -20,6 +20,14 @@ config EXAMPLES_LVGLDEMO_STACKSIZE
 	int "lvgldemo stack size"
 	default 16384
 
+config EXAMPLES_LVGLDEMO_UTOUCH_DEVPATH
+	string "Second pointer device path"
+	depends on INPUT_TOUCHSCREEN
+	---help---
+		Optional second pointer device, opened alongside the primary
+		touchscreen:  both drive the same UI.  A VNC server's remote
+		pointer device is the usual tenant.  Leave empty for none.
+
 config EXAMPLES_LVGLDEMO_INPUT_DEVPATH
 	string "Touchscreen device path"
 	default "/dev/input0"

examples/lvgldemo/lvgldemo.c

@@ -115,6 +115,18 @@ int main(int argc, FAR char *argv[])
 
 #ifdef CONFIG_INPUT_TOUCHSCREEN
   info.input_path = CONFIG_EXAMPLES_LVGLDEMO_INPUT_DEVPATH;
+#ifdef CONFIG_EXAMPLES_LVGLDEMO_UTOUCH_DEVPATH
+  /* A second pointer device, a VNC server's remote pointer, say,
+   * alongside the physical touchscreen rather than instead of it.  An
+   * empty string means none:  a string option always exists, only its
+   * content says whether it was configured.
+   */
+
+  if (CONFIG_EXAMPLES_LVGLDEMO_UTOUCH_DEVPATH[0] != '\0')
+    {
+      info.utouch_path = CONFIG_EXAMPLES_LVGLDEMO_UTOUCH_DEVPATH;
+    }
+#endif
 #endif
 
   lv_nuttx_init(&info, &result);