[demo] Move backend into an optional panel of WrapApp

egui_demo_lib/src/frame_history.rs

@@ -0,0 +1,126 @@
+use egui::util::History;
+
+pub struct FrameHistory {
+    frame_times: History<f32>,
+}
+
+impl Default for FrameHistory {
+    fn default() -> Self {
+        let max_age: f64 = 1.0;
+        Self {
+            frame_times: History::from_max_len_age((max_age * 300.0).round() as usize, max_age),
+        }
+    }
+}
+
+impl FrameHistory {
+    // Called first
+    pub fn on_new_frame(&mut self, now: f64, previus_frame_time: Option<f32>) {
+        let previus_frame_time = previus_frame_time.unwrap_or_default();
+        if let Some(latest) = self.frame_times.latest_mut() {
+            *latest = previus_frame_time; // rewrite history now that we know
+        }
+        self.frame_times.add(now, previus_frame_time); // projected
+    }
+
+    pub fn mean_frame_time(&self) -> f32 {
+        self.frame_times.average().unwrap_or_default()
+    }
+
+    pub fn fps(&self) -> f32 {
+        1.0 / self.frame_times.mean_time_interval().unwrap_or_default()
+    }
+
+    pub fn ui(&mut self, ui: &mut egui::Ui) {
+        ui.label(format!(
+            "Total frames painted: {}",
+            self.frame_times.total_count()
+        ))
+        .on_hover_text("Includes this frame.");
+
+        ui.label(format!(
+            "Mean CPU usage: {:.2} ms / frame",
+            1e3 * self.mean_frame_time()
+        ))
+        .on_hover_text(
+            "Includes Egui layout and tessellation time.\n\
+            Does not include GPU usage, nor overhead for sending data to GPU.",
+        );
+        egui::warn_if_debug_build(ui);
+
+        egui::CollapsingHeader::new("📊 CPU usage history")
+            .default_open(false)
+            .show(ui, |ui| {
+                self.graph(ui);
+            });
+    }
+
+    fn graph(&mut self, ui: &mut egui::Ui) -> egui::Response {
+        use egui::*;
+
+        let graph_top_cpu_usage = 0.010;
+        ui.label("Egui CPU usage history");
+
+        let history = &self.frame_times;
+
+        // TODO: we should not use `slider_width` as default graph width.
+        let height = ui.style().spacing.slider_width;
+        let size = vec2(ui.available_size_before_wrap_finite().x, height);
+        let response = ui.allocate_response(size, Sense::hover());
+        let rect = response.rect;
+        let style = ui.style().noninteractive();
+
+        let mut cmds = vec![PaintCmd::Rect {
+            rect,
+            corner_radius: style.corner_radius,
+            fill: ui.style().visuals.dark_bg_color,
+            stroke: ui.style().noninteractive().bg_stroke,
+        }];
+
+        let rect = rect.shrink(4.0);
+        let line_stroke = Stroke::new(1.0, Srgba::additive_luminance(128));
+
+        if let Some(mouse_pos) = ui.input().mouse.pos {
+            if rect.contains(mouse_pos) {
+                let y = mouse_pos.y;
+                cmds.push(PaintCmd::line_segment(
+                    [pos2(rect.left(), y), pos2(rect.right(), y)],
+                    line_stroke,
+                ));
+                let cpu_usage = remap(y, rect.bottom_up_range(), 0.0..=graph_top_cpu_usage);
+                let text = format!("{:.1} ms", 1e3 * cpu_usage);
+                cmds.push(PaintCmd::text(
+                    ui.fonts(),
+                    pos2(rect.left(), y),
+                    align::LEFT_BOTTOM,
+                    text,
+                    TextStyle::Monospace,
+                    color::WHITE,
+                ));
+            }
+        }
+
+        let circle_color = Srgba::additive_luminance(196);
+        let radius = 2.0;
+        let right_side_time = ui.input().time; // Time at right side of screen
+
+        for (time, cpu_usage) in history.iter() {
+            let age = (right_side_time - time) as f32;
+            let x = remap(age, history.max_age()..=0.0, rect.x_range());
+            let y = remap_clamp(cpu_usage, 0.0..=graph_top_cpu_usage, rect.bottom_up_range());
+
+            cmds.push(PaintCmd::line_segment(
+                [pos2(x, rect.bottom()), pos2(x, y)],
+                line_stroke,
+            ));
+
+            if cpu_usage < graph_top_cpu_usage {
+                cmds.push(PaintCmd::circle_filled(pos2(x, y), radius, circle_color));
+            }
+        }
+
+        ui.painter().extend(cmds);
+
+        response
+    }
+}