add plugin example

Cargo.toml

@@ -101,6 +101,10 @@ path = "examples/app/empty.rs"
 name = "headless"
 path = "examples/app/headless.rs"
 
+[[example]]
+name = "plugin"
+path = "examples/app/plugin.rs"
+
 [[example]]
 name = "event"
 path = "examples/ecs/event.rs"

examples/app/dynamic_plugin_loading/example_plugin/src/lib.rs

@@ -4,8 +4,8 @@ use bevy::prelude::*;
 pub struct ExamplePlugin;
 
 impl AppPlugin for ExamplePlugin {
-    fn build(&self, app_builder: &mut AppBuilder) {
-        app_builder.add_startup_system(setup);
+    fn build(&self, app: &mut AppBuilder) {
+        app.add_startup_system(setup);
     }
 }
 

examples/app/plugin.rs

@@ -0,0 +1,49 @@
+use bevy::prelude::*;
+use std::time::Duration;
+
+// Plugins are the foundation of Bevy. They are scoped sets of components, resources, and systems
+// that provide a specific piece of functionality (generally the smaller the scope, the better).
+fn main() {
+    App::build()
+        .add_default_plugins()
+        // plugins are registered as part of the "app building" process
+        .add_plugin(PrintMessagePlugin {
+            wait_duration: Duration::from_secs(1),
+            message: "This is an example plugin".to_string(),
+        })
+        .run();
+}
+
+#[derive(Default)]
+pub struct PrintMessagePlugin {
+    // Put your plugin configuration here
+    wait_duration: Duration,
+    message: String,
+}
+
+impl AppPlugin for PrintMessagePlugin {
+    // this is where we set up our plugin
+    fn build(&self, app: &mut AppBuilder) {
+        let state = PrintMessageState {
+            message: self.message.clone(),
+            elapsed_time: 0.0,
+            duration: self.wait_duration,
+        };
+        app.add_resource(state)
+            .add_system(print_message_system.system());
+    }
+}
+
+struct PrintMessageState {
+    message: String,
+    duration: Duration,
+    elapsed_time: f32,
+}
+
+fn print_message_system(time: Resource<Time>, mut state: ResourceMut<PrintMessageState>) {
+    state.elapsed_time += time.delta_seconds;
+    if state.elapsed_time > state.duration.as_secs_f32() {
+        println!("{}", state.message);
+        state.elapsed_time = 0.0;
+    }
+}