imgui-rs/imgui-glow-renderer/examples/glow_05_framebufferobject.rs

//! A basic example showing imgui rendering on top of a simple custom scene.

use std::{cell::RefCell, rc::Rc, time::Instant};

mod utils;

use glow::HasContext;
use utils::Triangler;

struct UserData {
    gl: Rc<glow::Context>,
    fbo: glow::NativeFramebuffer,
    _rbo: glow::NativeRenderbuffer,
}

const FBO_SIZE: i32 = 128;

fn main() {
    let (event_loop, window) = utils::create_window("Hello, FBO!", glutin::GlRequest::Latest);
    let (mut winit_platform, mut imgui_context) = utils::imgui_init(&window);
    let gl = utils::glow_context(&window);

    let mut ig_renderer = imgui_glow_renderer::AutoRenderer::initialize(gl, &mut imgui_context)
        .expect("failed to create renderer");
    let tri_renderer = Triangler::new(ig_renderer.gl_context(), "#version 330");

    let fbo;
    let rbo;
    unsafe {
        let gl = ig_renderer.gl_context();
        fbo = gl.create_framebuffer().unwrap();
        rbo = gl.create_renderbuffer().unwrap();

        gl.bind_framebuffer(glow::DRAW_FRAMEBUFFER, Some(fbo));
        gl.bind_renderbuffer(glow::RENDERBUFFER, Some(rbo));
        gl.renderbuffer_storage(glow::RENDERBUFFER, glow::RGBA8, FBO_SIZE, FBO_SIZE);
        gl.framebuffer_renderbuffer(
            glow::DRAW_FRAMEBUFFER,
            glow::COLOR_ATTACHMENT0,
            glow::RENDERBUFFER,
            Some(rbo),
        );
        gl.bind_renderbuffer(glow::RENDERBUFFER, None);

        gl.viewport(0, 0, FBO_SIZE, FBO_SIZE);
        tri_renderer.render(gl);

        gl.bind_framebuffer(glow::DRAW_FRAMEBUFFER, None);
    }

    let data = Rc::new(RefCell::new(UserData {
        gl: Rc::clone(ig_renderer.gl_context()),
        fbo,
        _rbo: rbo,
    }));

    let mut last_frame = Instant::now();
    event_loop.run(move |event, _, control_flow| {
        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(_) => {
                // Render your custom scene, note we need to borrow the OpenGL
                // context from the `AutoRenderer`, which takes ownership of it.
                unsafe {
                    ig_renderer.gl_context().clear(glow::COLOR_BUFFER_BIT);
                }

                let ui = imgui_context.frame();
                ui.show_demo_window(&mut true);
                ui.window("FBO").resizable(false).build(|| {
                    let pos = ui.cursor_screen_pos();
                    ui.set_cursor_screen_pos([pos[0] + FBO_SIZE as f32, pos[1] + FBO_SIZE as f32]);

                    let draws = ui.get_window_draw_list();
                    let scale = ui.io().display_framebuffer_scale;
                    let dsp_size = ui.io().display_size;
                    draws
                        .add_callback({
                            let data = Rc::clone(&data);
                            move || {
                                let data = data.borrow();
                                let gl = &*data.gl;
                                unsafe {
                                    let x = pos[0] * scale[0];
                                    let y = (dsp_size[1] - pos[1]) * scale[1];
                                    let dst_x0 = x as i32;
                                    let dst_y0 = (y - FBO_SIZE as f32 * scale[1]) as i32;
                                    let dst_x1 = (x + FBO_SIZE as f32 * scale[0]) as i32;
                                    let dst_y1 = y as i32;
                                    gl.scissor(dst_x0, dst_y0, dst_x1 - dst_x0, dst_y1 - dst_y0);
                                    gl.enable(glow::SCISSOR_TEST);
                                    gl.bind_framebuffer(glow::READ_FRAMEBUFFER, Some(data.fbo));
                                    gl.blit_framebuffer(
                                        0,
                                        0,
                                        FBO_SIZE,
                                        FBO_SIZE,
                                        dst_x0,
                                        dst_y0,
                                        dst_x1,
                                        dst_y1,
                                        glow::COLOR_BUFFER_BIT,
                                        glow::NEAREST,
                                    );
                                    gl.bind_framebuffer(glow::READ_FRAMEBUFFER, None);
                                }
                            }
                        })
                        .build();
                });

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

                // Render imgui on top of it
                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;
            }
            glutin::event::Event::LoopDestroyed => {
                let gl = ig_renderer.gl_context();
                tri_renderer.destroy(gl);
            }
            event => {
                winit_platform.handle_event(imgui_context.io_mut(), window.window(), &event);
            }
        }
    });
}