Add module ui.rs for the imgui integration

src/ui.rs

@@ -0,0 +1,84 @@
+use std::time::Instant;
+
+use anyhow::Result;
+use imgui::{Context as ImguiContext, Ui};
+use imgui_winit_support::{HiDpiMode, WinitPlatform};
+use imgui_glium_renderer::Renderer as ImguiGliumRenderer;
+use winit::window::Window;
+use glium::{Frame};
+use glium::glutin::surface::WindowSurface;
+
+/// Convenience wrapper that owns all ImGui state required for integration with
+/// winit + glium.
+pub struct Gui {
+    imgui:      ImguiContext,
+    platform:   WinitPlatform,
+    renderer:   ImguiGliumRenderer,
+    last_frame: Instant,
+}
+
+impl Gui {
+    pub fn new(display: &glium::Display<WindowSurface>, window: &Window) -> Result<Self> {
+        let mut imgui = ImguiContext::create();
+        imgui.set_ini_filename(None);
+        let mut platform = WinitPlatform::new(&mut imgui);
+        platform.attach_window(imgui.io_mut(), window, HiDpiMode::Default);
+        imgui.fonts().add_font(&[imgui::FontSource::DefaultFontData { config: None }]);
+        let renderer = ImguiGliumRenderer::new(&mut imgui, display)?;
+
+        Ok(Self {
+            imgui,
+            platform,
+            renderer,
+            last_frame: Instant::now(),
+        })
+    }
+
+    pub fn handle_event<T>(&mut self, window: &Window, event: &winit::event::Event<T>) {
+        self.platform
+            .handle_event(self.imgui.io_mut(), window, event);
+    }
+
+    pub fn prepare_frame(&mut self, window: &Window) {
+        let now = Instant::now();
+        self.imgui.io_mut().update_delta_time(now - self.last_frame);
+        self.last_frame = now;
+
+        self
+            .platform
+            .prepare_frame(self.imgui.io_mut(), window)
+            .expect("failed to prepare imgui frame");
+    }
+
+    pub fn render(&mut self, target: &mut Frame, window: &Window) {
+        let mut open = true;
+        self.render_with(target, window, |ui| {
+            ui.show_demo_window(&mut open);
+        });
+    }
+
+    pub fn render_with<F>(&mut self, target: &mut Frame, window: &Window, build_ui: F)
+    where
+        F: FnOnce(&Ui),
+    {
+        let ui = self.imgui.frame();
+
+        build_ui(&ui);
+
+        self.platform.prepare_render(ui, window);
+        let draw_data = self.imgui.render();
+
+        self
+            .renderer
+            .render(target, draw_data)
+            .expect("imgui rendering failed");
+    }
+
+    pub fn ui<F>(&mut self, build: F)
+    where
+        F: FnOnce(&Ui),
+    {
+        let ui = self.imgui.frame();
+        build(&ui);
+    }
+}