imgui-rs/imgui-glow-renderer/examples/01_basic.rs

//! A basic self-contained example to get you from zero-to-demo-window as fast
//! as possible.

use std::time::Instant;

use glow::HasContext;
use glutin::{event_loop::EventLoop, WindowedContext};
use imgui_winit_support::WinitPlatform;

const TITLE: &str = "Hello, imgui-rs!";

type Window = WindowedContext<glutin::PossiblyCurrent>;

fn main() {
    // Common setup for creating a winit window and imgui context, not specifc
    // to this renderer at all except that glutin is used to create the window
    // since it will give us access to a GL context
    let (event_loop, window) = create_window();
    let (mut winit_platform, mut imgui_context) = imgui_init(&window);

    // OpenGL context from glow
    let gl = glow_context(&window);

    // OpenGL renderer from this crate
    let mut ig_renderer = imgui_glow_renderer::AutoRenderer::initialize(gl, &mut imgui_context)
        .expect("failed to create renderer");

    let mut last_frame = Instant::now();

    // Standard winit event loop
    event_loop.run(move |event, _, control_flow| {
        *control_flow = glutin::event_loop::ControlFlow::Wait;
        match event {
            glutin::event::Event::NewEvents(_) => {
                let now = Instant::now();
                imgui_context
                    .io_mut()
                    .update_delta_time(now.duration_since(last_frame));
                last_frame = now;
            }
            glutin::event::Event::MainEventsCleared => {
                winit_platform
                    .prepare_frame(imgui_context.io_mut(), window.window())
                    .unwrap();
                window.window().request_redraw();
            }
            glutin::event::Event::RedrawRequested(_) => {
                // The renderer assumes you'll be clearing the buffer yourself
                unsafe { ig_renderer.gl_context().clear(glow::COLOR_BUFFER_BIT) };

                let ui = imgui_context.frame();
                ui.show_demo_window(&mut true);

                winit_platform.prepare_render(&ui, window.window());
                let draw_data = ui.render();

                // This is the only extra render step to add
                ig_renderer
                    .render(&draw_data)
                    .expect("error rendering imgui");

                window.swap_buffers().unwrap();
            }
            glutin::event::Event::WindowEvent {
                event: glutin::event::WindowEvent::CloseRequested,
                ..
            } => {
                *control_flow = glutin::event_loop::ControlFlow::Exit;
            }
            event => {
                winit_platform.handle_event(imgui_context.io_mut(), window.window(), &event);
            }
        }
    });
}

fn create_window() -> (EventLoop<()>, Window) {
    let event_loop = glutin::event_loop::EventLoop::new();
    let window = glutin::window::WindowBuilder::new()
        .with_title(TITLE)
        .with_inner_size(glutin::dpi::LogicalSize::new(1024, 768));
    let window = glutin::ContextBuilder::new()
        .with_vsync(true)
        .build_windowed(window, &event_loop)
        .expect("could not create window");
    let window = unsafe {
        window
            .make_current()
            .expect("could not make window context current")
    };
    (event_loop, window)
}

fn glow_context(window: &Window) -> glow::Context {
    unsafe { glow::Context::from_loader_function(|s| window.get_proc_address(s).cast()) }
}

fn imgui_init(window: &Window) -> (WinitPlatform, imgui::Context) {
    let mut imgui_context = imgui::Context::create();
    imgui_context.set_ini_filename(None);

    let mut winit_platform = WinitPlatform::init(&mut imgui_context);
    winit_platform.attach_window(
        imgui_context.io_mut(),
        window.window(),
        imgui_winit_support::HiDpiMode::Rounded,
    );

    imgui_context
        .fonts()
        .add_font(&[imgui::FontSource::DefaultFontData { config: None }]);

    imgui_context.io_mut().font_global_scale = (1.0 / winit_platform.hidpi_factor()) as f32;

    (winit_platform, imgui_context)
}