Add Shape::Callback to do custom rendering inside of an egui UI (#1351)

* Add Shape::Callback to do custom rendering inside of an egui UI
* Use Rc<glow::Context> everywhere
* Remove trait WebPainter
* Add glow::Context to epi::App::setup

eframe/examples/custom_3d.rs

@@ -0,0 +1,193 @@
+//! This demo shows how to embed 3D rendering using [`glow`](https://github.com/grovesNL/glow) in `eframe`.
+//!
+//! This is very advanced usage, and you need to be careful.
+//!
+//! If you want an easier way to show 3D graphics with egui, take a look at:
+//! * [`bevy_egui`](https://github.com/mvlabat/bevy_egui)
+//! * [`three-d`](https://github.com/asny/three-d)
+
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+
+use eframe::{egui, epi};
+
+use parking_lot::Mutex;
+use std::sync::Arc;
+
+#[derive(Default)]
+struct MyApp {
+    rotating_triangle: Arc<Mutex<Option<RotatingTriangle>>>,
+    angle: f32,
+}
+
+impl epi::App for MyApp {
+    fn name(&self) -> &str {
+        "Custom 3D painting inside an egui window"
+    }
+
+    fn update(&mut self, ctx: &egui::Context, _frame: &epi::Frame) {
+        egui::CentralPanel::default().show(ctx, |ui| {
+            ui.heading("Here is some 3D stuff:");
+
+            egui::ScrollArea::both().show(ui, |ui| {
+                egui::Frame::dark_canvas(ui.style()).show(ui, |ui| {
+                    self.custom_painting(ui);
+                });
+                ui.label("Drag to rotate!");
+            });
+        });
+
+        let mut frame = egui::Frame::window(&*ctx.style());
+        frame.fill = frame.fill.linear_multiply(0.5); // transparent
+        egui::Window::new("3D stuff in a window")
+            .frame(frame)
+            .show(ctx, |ui| {
+                self.custom_painting(ui);
+            });
+    }
+}
+
+impl MyApp {
+    fn custom_painting(&mut self, ui: &mut egui::Ui) {
+        let (rect, response) =
+            ui.allocate_exact_size(egui::Vec2::splat(256.0), egui::Sense::drag());
+
+        self.angle += response.drag_delta().x * 0.01;
+
+        let angle = self.angle;
+        let rotating_triangle = self.rotating_triangle.clone();
+
+        let callback = egui::epaint::PaintCallback {
+            rect,
+            callback: std::sync::Arc::new(move |render_ctx| {
+                if let Some(painter) = render_ctx.downcast_ref::<egui_glow::Painter>() {
+                    let mut rotating_triangle = rotating_triangle.lock();
+                    let rotating_triangle = rotating_triangle
+                        .get_or_insert_with(|| RotatingTriangle::new(painter.gl()));
+                    rotating_triangle.paint(painter.gl(), angle);
+                } else {
+                    eprintln!("Can't do custom painting because we are not using a glow context");
+                }
+            }),
+        };
+        ui.painter().add(callback);
+    }
+}
+
+struct RotatingTriangle {
+    program: glow::Program,
+    vertex_array: glow::VertexArray,
+}
+
+impl RotatingTriangle {
+    fn new(gl: &glow::Context) -> Self {
+        use glow::HasContext as _;
+
+        let shader_version = if cfg!(target_arch = "wasm32") {
+            "#version 300 es"
+        } else {
+            "#version 410"
+        };
+
+        unsafe {
+            let program = gl.create_program().expect("Cannot create program");
+
+            let (vertex_shader_source, fragment_shader_source) = (
+                r#"
+                    const vec2 verts[3] = vec2[3](
+                        vec2(0.0, 1.0),
+                        vec2(-1.0, -1.0),
+                        vec2(1.0, -1.0)
+                    );
+                    const vec4 colors[3] = vec4[3](
+                        vec4(1.0, 0.0, 0.0, 1.0),
+                        vec4(0.0, 1.0, 0.0, 1.0),
+                        vec4(0.0, 0.0, 1.0, 1.0)
+                    );
+                    out vec4 v_color;
+                    uniform float u_angle;
+                    void main() {
+                        v_color = colors[gl_VertexID];
+                        gl_Position = vec4(verts[gl_VertexID], 0.0, 1.0);
+                        gl_Position.x *= cos(u_angle);
+                    }
+                "#,
+                r#"
+                    precision mediump float;
+                    in vec4 v_color;
+                    out vec4 out_color;
+                    void main() {
+                        out_color = v_color;
+                    }
+                "#,
+            );
+
+            let shader_sources = [
+                (glow::VERTEX_SHADER, vertex_shader_source),
+                (glow::FRAGMENT_SHADER, fragment_shader_source),
+            ];
+
+            let shaders: Vec<_> = shader_sources
+                .iter()
+                .map(|(shader_type, shader_source)| {
+                    let shader = gl
+                        .create_shader(*shader_type)
+                        .expect("Cannot create shader");
+                    gl.shader_source(shader, &format!("{}\n{}", shader_version, shader_source));
+                    gl.compile_shader(shader);
+                    if !gl.get_shader_compile_status(shader) {
+                        panic!("{}", gl.get_shader_info_log(shader));
+                    }
+                    gl.attach_shader(program, shader);
+                    shader
+                })
+                .collect();
+
+            gl.link_program(program);
+            if !gl.get_program_link_status(program) {
+                panic!("{}", gl.get_program_info_log(program));
+            }
+
+            for shader in shaders {
+                gl.detach_shader(program, shader);
+                gl.delete_shader(shader);
+            }
+
+            let vertex_array = gl
+                .create_vertex_array()
+                .expect("Cannot create vertex array");
+
+            Self {
+                program,
+                vertex_array,
+            }
+        }
+    }
+
+    // TODO: figure out how to call this in a nice way
+    #[allow(unused)]
+    fn destroy(self, gl: &glow::Context) {
+        use glow::HasContext as _;
+        unsafe {
+            gl.delete_program(self.program);
+            gl.delete_vertex_array(self.vertex_array);
+        }
+    }
+
+    fn paint(&self, gl: &glow::Context, angle: f32) {
+        use glow::HasContext as _;
+        unsafe {
+            gl.use_program(Some(self.program));
+            gl.uniform_1_f32(
+                gl.get_uniform_location(self.program, "u_angle").as_ref(),
+                angle,
+            );
+            gl.bind_vertex_array(Some(self.vertex_array));
+            gl.draw_arrays(glow::TRIANGLES, 0, 3);
+        }
+    }
+}
+
+fn main() {
+    let options = eframe::NativeOptions::default();
+    eframe::run_native(Box::new(MyApp::default()), options);
+}

eframe/examples/custom_font.rs

@@ -22,6 +22,7 @@ impl epi::App for MyApp {
         ctx: &egui::Context,
         _frame: &epi::Frame,
         _storage: Option<&dyn epi::Storage>,
+        _gl: &std::rc::Rc<epi::glow::Context>,
     ) {
         // Start with the default fonts (we will be adding to them rather than replacing them).
         let mut fonts = egui::FontDefinitions::default();