Render a ghost stone over the current cursor location

kifu/kifu-gtk/src/ui/goban.rs

@@ -6,11 +6,18 @@ use std::{cell::RefCell, rc::Rc};
 const WIDTH: i32 = 800;
 const HEIGHT: i32 = 800;
 
+#[derive(Clone, Default, PartialEq)]
+struct Addr {
+    row: u8,
+    column: u8,
+}
+
 #[derive(Default)]
 pub struct GobanPrivate {
     drawing_area: gtk::DrawingArea,
 
     goban: Rc<RefCell<GobanElement>>,
+    cursor_location: Rc<RefCell<Addr>>,
 }
 
 #[glib::object_subclass]
@@ -26,6 +33,7 @@ impl ObjectImpl for GobanPrivate {
         self.drawing_area.set_height_request(HEIGHT);
 
         let goban = self.goban.clone();
+        let cursor_location = self.cursor_location.clone();
         self.drawing_area
             .set_draw_func(move |_, context, width, height| {
                 let goban = goban.borrow();
@@ -72,7 +80,36 @@ impl ObjectImpl for GobanPrivate {
                         };
                     })
                 });
+
+                let cursor = cursor_location.borrow();
+                pen.ghost_stone(context, cursor.row, cursor.column, Color::White);
             });
+
+        let motion_controller = gtk::EventControllerMotion::new();
+        {
+            let goban = self.goban.clone();
+            let cursor = self.cursor_location.clone();
+            let drawing_area = self.drawing_area.clone();
+            motion_controller.connect_motion(move |_, x, y| {
+                let goban = goban.borrow();
+                let mut cursor = cursor.borrow_mut();
+                let hspace_between = ((WIDTH - 40) as f64) / ((goban.size.width - 1) as f64);
+                let vspace_between = ((HEIGHT - 40) as f64) / ((goban.size.height - 1) as f64);
+
+                let addr = Addr {
+                    column: ((x.round() - 20.) / hspace_between).round() as u8,
+                    row: ((y.round() - 20.) / vspace_between).round() as u8,
+                };
+
+                if *cursor != addr {
+                    println!("redrawing with cursor at {} {}", addr.row, addr.column);
+                    *cursor = addr;
+                    drawing_area.queue_draw();
+                }
+            });
+        }
+
+        self.drawing_area.add_controller(motion_controller);
     }
 }
 impl WidgetImpl for GobanPrivate {}
@@ -128,4 +165,19 @@ impl Pen {
         );
         let _ = context.fill();
     }
+
+    fn ghost_stone(&self, context: &cairo::Context, row: u8, col: u8, color: Color) {
+        match color {
+            Color::White => context.set_source_rgba(0.9, 0.9, 0.9, 0.5),
+            Color::Black => context.set_source_rgba(0.0, 0.0, 0.0, 0.5),
+        };
+        context.arc(
+            20.0 + (col as f64) * self.hspace_between,
+            20.0 + (row as f64) * self.vspace_between,
+            25.0,
+            0.0,
+            2.0 * std::f64::consts::PI,
+        );
+        let _ = context.fill();
+    }
 }