Encapsulate dragging logic

src/bin/wireframe/main.rs

@@ -1,11 +1,11 @@
-use glam::{mat4, vec2, vec3, vec4, Mat4, Quat, Vec3};
+use glam::{mat4, vec2, vec3, vec4, Mat4, Quat, Vec2, Vec3};
 use glium::{
 	backend::glutin::SimpleWindowBuilder,
 	implement_vertex, uniform,
 	winit::event::{Event, WindowEvent},
 	Program, Surface, VertexBuffer,
 };
-use winit::event_loop::EventLoop;
+use winit::{event::ElementState, event_loop::EventLoop};
 
 #[derive(Copy, Clone)]
 struct Vertex {
@@ -13,6 +13,40 @@ struct Vertex {
 }
 implement_vertex!(Vertex, position);
 
+struct DragCtl<S> {
+	state: S,
+	ctl: Option<(Vec2, S)>,
+}
+
+impl<S: Copy> DragCtl<S> {
+	pub fn new(state: S) -> Self {
+		Self { state, ctl: None }
+	}
+
+	pub fn state(&self) -> S {
+		self.state
+	}
+
+	pub fn on_button(&mut self, pos: Vec2, state: ElementState) {
+		match state {
+			ElementState::Pressed => {
+				assert!(self.ctl.is_none());
+				self.ctl = Some((pos, self.state));
+			}
+			ElementState::Released => {
+				assert!(self.ctl.is_some());
+				self.ctl = None;
+			}
+		}
+	}
+
+	pub fn on_move(&mut self, pos: Vec2, f: impl FnOnce(S, Vec2) -> S) {
+		if let Some((old_pos, old_state)) = self.ctl {
+			self.state = f(old_state, pos - old_pos);
+		}
+	}
+}
+
 fn main() {
 	let event_loop = EventLoop::builder().build().unwrap();
 	let (window, display) = SimpleWindowBuilder::new()
@@ -41,8 +75,7 @@ fn main() {
 	let vertex_buffer = VertexBuffer::new(&display, &shape).unwrap();
 
 	let mut cur_pos = vec2(0., 0.);
-	let mut drag_start = None;
-	let mut cam_rot = Quat::IDENTITY;
+	let mut cam_rot = DragCtl::new(Quat::IDENTITY);
 
 	#[allow(deprecated)]
 	event_loop
@@ -54,7 +87,7 @@ fn main() {
 						* std::f32::consts::SQRT_2;
 					let proj = make_proj_matrix(vec3(size.x, size.y, 2.), (0.125, 1024.125));
 
-					let view = Mat4::from_quat(cam_rot);
+					let view = Mat4::from_quat(cam_rot.state());
 
 					let mut target = display.draw();
 					target.clear_color(0.0, 0.0, 0.2, 1.0);
@@ -81,12 +114,7 @@ fn main() {
 					state,
 					button,
 				} => match button {
-					winit::event::MouseButton::Left => match state {
-						winit::event::ElementState::Pressed => {
-							drag_start = Some((cur_pos, cam_rot))
-						}
-						winit::event::ElementState::Released => drag_start = None,
-					},
+					winit::event::MouseButton::Left => cam_rot.on_button(cur_pos, state),
 					_ => {}
 				},
 
@@ -97,12 +125,10 @@ fn main() {
 					let size = window.inner_size();
 					let size = vec2(size.width as f32, size.height as f32);
 					cur_pos = vec2(position.x as f32, position.y as f32) / size;
-					if let Some((drag_start, drag_init_rot)) = drag_start {
-						let offset = cur_pos - drag_start;
-						cam_rot = Quat::from_euler(glam::EulerRot::YXZ, offset.x, offset.y, 0.)
-							* drag_init_rot;
+					cam_rot.on_move(cur_pos, |init, off| {
 						window.request_redraw();
-					}
+						Quat::from_euler(glam::EulerRot::YXZ, off.x, off.y, 0.) * init
+					});
 				}
 
 				WindowEvent::Resized(window_size) => {