Add FPS counter to top-left of screen

assets/ui/fps.ron

@@ -0,0 +1,18 @@
+#![enable(implicit_some)]
+Label(
+    transform: (
+        id: "fps_text",
+        anchor: TopLeft,
+        x: 100.,
+        y: -25.,
+        width: 200.,
+        height: 50.,
+        transparent: true,
+    ),
+    text: (
+        text: "N/A",
+        font_size: 25.,
+        color: (1., 1., 1., 1.),
+        font: File("font/square.ttf", ("TTF", ())),
+    ),
+)

src/main.rs

@@ -18,7 +18,8 @@ use amethyst::{
         types::DefaultBackend,
         RenderingBundle,
     },
-    utils::application_root_dir,
+    ui::{RenderUi, UiBundle},
+    utils::{application_root_dir, fps_counter::FpsCounterBundle},
     Application, GameDataBuilder,
 };
 
@@ -56,7 +57,10 @@ fn main() -> amethyst::Result<()> {
                 .with_dep(&["sprite_animation_control", "sprite_sampler_interpolation"]),
         )?
         .with_bundle(input_bundle)?
+        .with_bundle(FpsCounterBundle {})?
+        .with_bundle(UiBundle::<StringBindings>::new())?
         .with(Processor::<Map>::new(), "map_processor", &[])
+        .with(UiFpsSystem::default(), "ui_fps_system", &[])
         .with(MarineInputSystem, "marine_input_system", &[])
         .with(
             MarineKinematicsSystem,
@@ -139,7 +143,8 @@ fn main() -> amethyst::Result<()> {
                     RenderToWindow::from_config_path(display_config_path)
                         .with_clear([0.008, 0.043, 0.067, 1.0]),
                 )
-                .with_plugin(RenderFlat2D::default()),
+                .with_plugin(RenderFlat2D::default())
+                .with_plugin(RenderUi::default()),
         )?;
     let mut game =
         Application::build(assets_path, states::LoadState::default())?.build(game_data)?;

src/states/load.rs

@@ -1,6 +1,7 @@
 use amethyst::{
     assets::{AssetStorage, Handle, JsonFormat, Loader, ProgressCounter},
     prelude::{GameData, SimpleState, SimpleTrans, StateData, Trans},
+    ui::UiCreator,
 };
 
 use crate::{
@@ -33,6 +34,8 @@ impl SimpleState for LoadState {
                 AssetType::Truss,
             ],
         ));
+        let mut progress = ProgressCounter::default();
+        world.exec(|mut creator: UiCreator<'_>| creator.create("ui/fps.ron", &mut progress));
         self.map_handle = {
             let loader = world.read_resource::<Loader>();
             Some(loader.load(

src/systems/mod.rs

@@ -7,6 +7,7 @@ mod kinematics;
 mod parallax;
 mod pincer;
 mod transformation;
+mod ui;
 
 pub use self::animation::AnimationControlSystem;
 pub use self::animation::BulletImpactAnimationSystem;
@@ -27,3 +28,4 @@ pub use self::pincer::PincerAiSystem;
 pub use self::transformation::BulletTransformationSystem;
 pub use self::transformation::CameraTransformationSystem;
 pub use self::transformation::TransformationSystem;
+pub use self::ui::*;

src/systems/ui/fps.rs

@@ -0,0 +1,40 @@
+use amethyst::{
+    core::Time,
+    ecs::prelude::{Entity, Read, System, WriteStorage},
+    ui::{UiFinder, UiText},
+    utils::fps_counter::FpsCounter,
+};
+
+/// Every 20 frames, this system updates the UI component for the FPS counter.
+///
+/// Source: The FPS counter, including font, assets/ui/fps.ron and this system was originally
+/// copied from the Amethyst examples.
+#[derive(Default)]
+pub struct UiFpsSystem {
+    fps_display: Option<Entity>,
+}
+
+impl<'a> System<'a> for UiFpsSystem {
+    type SystemData = (
+        Read<'a, Time>,
+        WriteStorage<'a, UiText>,
+        Read<'a, FpsCounter>,
+        UiFinder<'a>,
+    );
+
+    fn run(&mut self, (time, mut ui_text, fps_counter, finder): Self::SystemData) {
+        if self.fps_display.is_none() {
+            if let Some(fps_entity) = finder.find("fps_text") {
+                self.fps_display = Some(fps_entity);
+            }
+        }
+        if let Some(fps_entity) = self.fps_display {
+            if let Some(fps_display) = ui_text.get_mut(fps_entity) {
+                if time.frame_number() % 20 == 0 {
+                    let fps = fps_counter.sampled_fps();
+                    fps_display.text = format!("FPS: {:.*}", 2, fps);
+                }
+            }
+        }
+    }
+}

src/systems/ui/mod.rs

@@ -0,0 +1,3 @@
+mod fps;
+
+pub use self::fps::UiFpsSystem;