small corrections + poc004 webcam screenshot/webcam register

poc004/src/main.rs

@@ -0,0 +1,54 @@
+// file: poc-qt/poc004/src/main.rs
+
+use cxx_qt_lib::{QGuiApplication, QQmlApplicationEngine, QString, QUrl};
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    let mut app = QGuiApplication::new();
+    let mut engine = QQmlApplicationEngine::new();
+
+    let current_dir = match env::current_dir() {
+        Ok(v) => v,
+        Err(err) => {
+            eprintln!("failed to get current_dir: {err}");
+            return;
+        }
+    };
+
+    let main_qml_path: PathBuf = current_dir.join("qml/main.qml");
+    let main_qml_path = match main_qml_path.canonicalize() {
+        Ok(v) => v,
+        Err(err) => {
+            eprintln!(
+                "failed to resolve qml/main.qml from {}: {err}",
+                main_qml_path.display()
+            );
+            return;
+        }
+    };
+
+    let main_qml_str = match main_qml_path.to_str() {
+        Some(v) => v.to_string(),
+        None => {
+            eprintln!("qml path is not valid UTF-8: {}", main_qml_path.display());
+            return;
+        }
+    };
+
+    println!("loading qml from: {}", main_qml_str);
+
+    if let Some(engine_ref) = engine.as_mut() {
+        let qml_url = QUrl::from_local_file(&QString::from(main_qml_str));
+        engine_ref.load(&qml_url);
+    } else {
+        eprintln!("failed to create QQmlApplicationEngine");
+        return;
+    }
+
+    if let Some(app_ref) = app.as_mut() {
+        app_ref.exec();
+    } else {
+        eprintln!("failed to create QGuiApplication");
+    }
+}