Viewport frame-rate readout (Preferences ▸ Graphics) (#1580)

Thanks @sthifen.

crates/ui-egui/src/frame_rate.rs

@@ -0,0 +1,96 @@
+//! The viewport's frame-rate readout (Preferences ▸ Graphics ▸ "Frame rate").
+
+use egui::{FontId, Rect, Stroke, pos2, vec2};
+
+use crate::SolveApp;
+use crate::theme::Tokens;
+
+/// Weight of the newest frame in the running mean (roughly the last 20 frames count).
+const NEWEST: f64 = 0.05;
+
+/// Frames per second, averaged over recent frames.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct FrameRate {
+    mean_dt: f64,
+}
+
+impl FrameRate {
+    /// Takes the time since the previous frame, in seconds. A gap over a second (the app idle
+    /// before the readout was turned on, a window being moved) is not a frame of a running view
+    /// and is left out, as is anything that isn't a positive finite time.
+    pub fn record(&mut self, dt: f64) {
+        if !dt.is_finite() || dt <= 0.0 || dt > 1.0 {
+            return;
+        }
+        self.mean_dt = if self.mean_dt > 0.0 { self.mean_dt + NEWEST * (dt - self.mean_dt) } else { dt };
+    }
+
+    /// The averaged rate; `None` before the first frame was recorded.
+    pub fn fps(&self) -> Option<f64> {
+        (self.mean_dt > 0.0).then(|| 1.0 / self.mean_dt)
+    }
+
+    /// The readout's text: rate and the matching time per frame.
+    pub fn label(&self) -> Option<String> {
+        self.fps().map(|fps| format!("{fps:.0} FPS · {:.1} ms", 1000.0 * self.mean_dt))
+    }
+}
+
+/// Records this frame and paints the readout in the view's bottom-right corner. While it is on
+/// the view redraws every frame, so the rate is what the view can draw rather than how often
+/// something happened to change.
+pub(crate) fn paint(app: &mut SolveApp, ctx: &egui::Context, painter: &egui::Painter, rect: Rect) {
+    if !app.preferences.show_frame_rate {
+        app.frame_rate = FrameRate::default();
+        return;
+    }
+    app.frame_rate.record(f64::from(ctx.input(|i| i.unstable_dt)));
+    ctx.request_repaint();
+    let Some(text) = app.frame_rate.label() else { return };
+    let t = Tokens::get();
+    let font = FontId::monospace(12.0);
+    let galley = painter.layout_no_wrap(text, font, t.text);
+    let size = galley.size() + vec2(16.0, 8.0);
+    let r = Rect::from_min_size(pos2(rect.right() - 12.0 - size.x, rect.bottom() - 12.0 - size.y), size);
+    painter.rect(r, 4.0, t.overlay, Stroke::new(1.0, t.border), egui::StrokeKind::Inside);
+    crate::scenario::publish_handle("viewport:frame_rate", r.center());
+    painter.galley(r.center() - galley.size() / 2.0, galley, t.text);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::FrameRate;
+
+    #[test]
+    fn steady_frames_read_their_rate() {
+        let mut f = FrameRate::default();
+        assert_eq!(f.fps(), None);
+        for _ in 0..200 {
+            f.record(1.0 / 60.0);
+        }
+        assert!((f.fps().unwrap_or(0.0) - 60.0).abs() < 1e-6);
+        assert_eq!(f.label().as_deref(), Some("60 FPS · 16.7 ms"));
+    }
+
+    #[test]
+    fn pauses_and_hostile_times_are_left_out() {
+        let mut f = FrameRate::default();
+        for dt in [0.0, -1.0, f64::NAN, f64::INFINITY, 5.0] {
+            f.record(dt);
+        }
+        assert_eq!(f.fps(), None);
+        f.record(0.01);
+        f.record(3.0);
+        assert!((f.fps().unwrap_or(0.0) - 100.0).abs() < 1e-6);
+    }
+
+    #[test]
+    fn the_mean_follows_a_slower_view() {
+        let mut f = FrameRate::default();
+        f.record(1.0 / 120.0);
+        for _ in 0..300 {
+            f.record(1.0 / 30.0);
+        }
+        assert!((f.fps().unwrap_or(0.0) - 30.0).abs() < 0.1);
+    }
+}

crates/ui-egui/src/lib.rs

@@ -44,6 +44,7 @@ pub mod drag_snap;
 pub mod edit_clipboard;
 pub mod fonts;
 pub mod frame;
+pub mod frame_rate;
 pub mod gizmo;
 pub mod gpu;
 pub mod help;
@@ -353,6 +354,8 @@ pub struct SolveApp {
     /// [`SolveApp::set_wgpu`].
     pub cpu_meshing: bool,
     pub frame_ms: f64,
+    /// The viewport's frame-rate readout ([`frame_rate`]).
+    pub frame_rate: frame_rate::FrameRate,
     pub synthetic: Vec<egui::Event>,
     /// The modifiers of the synthetic press in progress (a Ctrl-drag keeps Ctrl while it moves).
     pub synthetic_mods: egui::Modifiers,
@@ -446,6 +449,7 @@ impl SolveApp {
             integrated_titlebar: false,
             cpu_meshing: false,
             frame_ms: 0.0,
+            frame_rate: frame_rate::FrameRate::default(),
             synthetic: Vec::new(),
             synthetic_mods: egui::Modifiers::default(),
             control_rx: None,

crates/ui-egui/src/prefs.rs

@@ -283,6 +283,8 @@ pub struct Prefs {
     pub supersampling: f32,
     /// Supersample only while the view holds still (full speed while orbiting).
     pub supersampling_adaptive: bool,
+    /// Show the frame rate in the view's corner (the view then redraws every frame).
+    pub show_frame_rate: bool,
     /// Show world X/Y/Z component dimensions beside the total distance in Measure.
     pub measure_axis_distances: bool,
     /// Decimals shown for lengths and angles.
@@ -400,6 +402,7 @@ impl Default for Prefs {
             display_quality: "normal".into(),
             supersampling: 1.0,
             supersampling_adaptive: true,
+            show_frame_rate: false,
             measure_axis_distances: true,
             length_decimals: 2,
             angle_decimals: 1,
@@ -624,6 +627,7 @@ fn defaults(app: &mut SolveApp, page: usize) {
             p.display_quality = d.display_quality;
             p.supersampling = d.supersampling;
             p.supersampling_adaptive = d.supersampling_adaptive;
+            p.show_frame_rate = d.show_frame_rate;
             p.measure_axis_distances = d.measure_axis_distances;
             p.color_vision = d.color_vision;
             app.ui.visual_style = 0;
@@ -1310,6 +1314,13 @@ fn page(app: &mut SolveApp, ui: &mut egui::Ui, t: &Tokens) {
             colour_vision_sample(ui, t);
             ui.end_row();
             note(ui, app.tr("ui.colour_vision_note"));
+            // Last, so the colour vision section above keeps its place on the page.
+            ui.label("");
+            ui.end_row();
+            ui.label(app.tr("ui.frame_rate"));
+            ui.checkbox(&mut app.preferences.show_frame_rate, "");
+            ui.end_row();
+            note(ui, app.tr("settings.frame_rate_note"));
         }
         5 => {
             ui.label(crate::i18n::tr_label("Project face edges into new sketches"));

crates/ui-egui/src/viewport.rs

@@ -2237,6 +2237,7 @@ pub fn show(app: &mut SolveApp, ui: &mut egui::Ui) {
         painter.add(egui_wgpu::Callback::new_paint_callback(rect, cb));
     }
     analysis_legend(app, &painter, rect);
+    crate::frame_rate::paint(app, ui.ctx(), &painter, rect);
 
     // ---- interaction ----
     let add = mods.shift || mods.command || mods.ctrl;