Add callbacks to the draw_list.

imgui-glow-renderer/examples/glow_05_framebufferobject.rs

@@ -0,0 +1,150 @@
+//! 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);
+            }
+        }
+    });
+}

imgui-glow-renderer/src/lib.rs

@@ -45,7 +45,7 @@
 //! is sRGB (if you don't know, it probably is) the `internal_format` is
 //! one of the `SRGB*` values.
 
-use std::{borrow::Cow, error::Error, fmt::Display, mem::size_of, num::NonZeroU32};
+use std::{borrow::Cow, error::Error, fmt::Display, mem::size_of, num::NonZeroU32, rc::Rc};
 
 use imgui::{internal::RawWrapper, DrawCmd, DrawData, DrawVert};
 
@@ -71,7 +71,7 @@ type GlUniformLocation = <Context as HasContext>::UniformLocation;
 /// OpenGL context is still available to the rest of the application through
 /// the [`gl_context`](Self::gl_context) method.
 pub struct AutoRenderer {
-    gl: glow::Context,
+    gl: Rc<glow::Context>,
     texture_map: SimpleTextureMap,
     renderer: Renderer,
 }
@@ -87,7 +87,7 @@ impl AutoRenderer {
         let mut texture_map = SimpleTextureMap::default();
         let renderer = Renderer::initialize(&gl, imgui_context, &mut texture_map, true)?;
         Ok(Self {
-            gl,
+            gl: Rc::new(gl),
             texture_map,
             renderer,
         })
@@ -96,7 +96,7 @@ impl AutoRenderer {
     /// Note: no need to provide a `mut` version of this, as all methods on
     /// [`glow::HasContext`] are immutable.
     #[inline]
-    pub fn gl_context(&self) -> &glow::Context {
+    pub fn gl_context(&self) -> &Rc<glow::Context> {
         &self.gl
     }
 

imgui/src/draw_list.rs

@@ -16,7 +16,7 @@
 use bitflags::bitflags;
 
 use crate::{math::MintVec2, ImColor32};
-use sys::ImDrawList;
+use sys::{ImDrawCmd, ImDrawList};
 
 use super::Ui;
 use crate::render::renderer::TextureId;
@@ -468,6 +468,14 @@ impl<'ui> DrawListMut<'ui> {
     ) -> ImageRounded<'_> {
         ImageRounded::new(self, texture_id, p_min, p_max, rounding)
     }
+
+    /// Draw the specified callback.
+    ///
+    /// Note: if this DrawList is never rendered the callback will leak because DearImGui
+    /// does not provide a method to clean registered callbacks.
+    pub fn add_callback<F: FnOnce() + 'static>(&'ui self, callback: F) -> Callback<'ui, F> {
+        Callback::new(self, callback)
+    }
 }
 
 /// Represents a line about to be drawn
@@ -1186,3 +1194,45 @@ impl<'ui> ImageRounded<'ui> {
         }
     }
 }
+
+#[must_use = "should call .build() to draw the object"]
+pub struct Callback<'ui, F> {
+    draw_list: &'ui DrawListMut<'ui>,
+    callback: F,
+}
+
+impl<'ui, F: FnOnce() + 'static> Callback<'ui, F> {
+    /// Typically constructed by [`DrawListMut::add_callback`]
+    pub fn new(draw_list: &'ui DrawListMut<'_>, callback: F) -> Self {
+        Callback {
+            draw_list,
+            callback,
+        }
+    }
+    /// Adds the callback to the draw-list so it will be run when the window is drawn
+    pub fn build(self) {
+        use std::os::raw::c_void;
+        // F is Sized, so *mut F must be a thin pointer.
+        let callback: *mut F = Box::into_raw(Box::new(self.callback));
+
+        unsafe {
+            sys::ImDrawList_AddCallback(
+                self.draw_list.draw_list,
+                Some(Self::run_callback),
+                callback as *mut c_void,
+            );
+        }
+    }
+    unsafe extern "C" fn run_callback(_parent_list: *const ImDrawList, cmd: *const ImDrawCmd) {
+        // We are modifying through a C const pointer, but that should be harmless.
+        let cmd = &mut *(cmd as *mut ImDrawCmd);
+        // Consume the pointer and leave a NULL behind to avoid a double-free or
+        // calling twice an FnOnce. It should not happen, but better safe than sorry.
+        let callback = std::mem::replace(&mut cmd.UserCallbackData, std::ptr::null_mut());
+        if callback.is_null() {
+            return;
+        }
+        let callback = Box::from_raw(callback as *mut F);
+        callback();
+    }
+}