PixelPaint: Open image file passed as argument

This is obviously a requirement for #5374, oops :^)

Also handle errors gracefully, opening a file that isn't PixelPaint JSON
would previously crash.

Closes #5388.

Userland/Applications/PixelPaint/main.cpp

@@ -36,6 +36,8 @@
 #include "Tool.h"
 #include "ToolPropertiesWidget.h"
 #include "ToolboxWidget.h"
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/Application.h>
 #include <LibGUI/BoxLayout.h>
@@ -65,6 +67,11 @@ int main(int argc, char** argv)
         return 1;
     }
 
+    const char* image_file = nullptr;
+    Core::ArgsParser args_parser;
+    args_parser.add_positional_argument(image_file, "PixelPaint image file (*.pp) to open", "path", Core::ArgsParser::Required::No);
+    args_parser.parse(argc, argv);
+
     auto app_icon = GUI::Icon::default_icon("app-pixel-paint");
 
     auto window = GUI::Window::construct();
@@ -93,6 +100,9 @@ int main(int argc, char** argv)
     right_panel.set_layout<GUI::VerticalBoxLayout>();
 
     auto& layer_list_widget = right_panel.add<PixelPaint::LayerListWidget>();
+    layer_list_widget.on_layer_select = [&](auto* layer) {
+        image_editor.set_active_layer(layer);
+    };
 
     auto& layer_properties_widget = right_panel.add<PixelPaint::LayerPropertiesWidget>();
 
@@ -108,6 +118,16 @@ int main(int argc, char** argv)
     auto menubar = GUI::MenuBar::construct();
     auto& app_menu = menubar->add_menu("PixelPaint");
 
+    auto open_image_file = [&](auto& path) {
+        auto image = PixelPaint::Image::create_from_file(path);
+        if (!image) {
+            GUI::MessageBox::show_error(window, String::formatted("Invalid image file: {}", path));
+            return;
+        }
+        image_editor.set_image(image);
+        layer_list_widget.set_image(image);
+    };
+
     app_menu.add_action(
         GUI::Action::create(
             "New", [&](auto&) {
@@ -130,9 +150,7 @@ int main(int argc, char** argv)
         if (!open_path.has_value())
             return;
 
-        auto image = PixelPaint::Image::create_from_file(open_path.value());
+        open_image_file(open_path.value());
-        image_editor.set_image(image);
-        layer_list_widget.set_image(image);
     }));
     app_menu.add_action(GUI::CommonActions::make_save_as_action([&](auto&) {
         if (!image_editor.image())
@@ -372,6 +390,10 @@ int main(int argc, char** argv)
         layer_properties_widget.set_layer(layer);
     };
 
+    auto image_file_real_path = Core::File::real_path_for(image_file);
+    if (Core::File::exists(image_file_real_path)) {
+        open_image_file(image_file_real_path);
+    } else {
         auto image = PixelPaint::Image::create_with_size({ 640, 480 });
 
         auto bg_layer = PixelPaint::Layer::create_with_size(*image, { 640, 480 }, "Background");
@@ -388,14 +410,11 @@ int main(int argc, char** argv)
         image->add_layer(*fg_layer2);
         fg_layer2->bitmap().fill(Color::Blue);
 
-    layer_list_widget.on_layer_select = [&](auto* layer) {
-        image_editor.set_active_layer(layer);
-    };
-
         layer_list_widget.set_image(image);
 
         image_editor.set_image(image);
         image_editor.set_active_layer(bg_layer);
+    }
 
     return app->exec();
 }