Make map draggable

The map can be dragged around, but since the grid is not yet infinitely
big, it feels quite weird to zoom and drag

2 files changed, 33 insertions, 4 deletions

diff --git a/src/main.rs b/src/main.rs
index 284ee53..81677e2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -40,12 +40,21 @@ fn main() {
     // Line used to draw the square grid.
     let grid_line = Line::new([1., 1., 1., 0.3], 1.5);
 
+    let mut mouse_pos_px = [0., 0.];
     let mut mouse_pos_m = [0., 0.];
     let mut events = Events::new(EventSettings::new().lazy(true));
+    let mut canvas_follows_mouse = false;
     while let Some(e) = events.next(&mut window) {
-        // Update the mouse cursor position
-        e.mouse_cursor(|pos| {
-            mouse_pos_m = transform.point_px_to_m(pos);
+        // Update the mouse cursor position and possibly the canvas position too, in case the user
+        // is currently dragging the canvas.
+        e.mouse_cursor(|new_pos| {
+            if canvas_follows_mouse {
+                let move_by = math::sub(new_pos, mouse_pos_px);
+                transform.move_by_px(move_by);
+            }
+
+            mouse_pos_px = new_pos;
+            mouse_pos_m = transform.point_px_to_m(new_pos);
         });
 
         // The zoom factor is changed with the mouse wheel.
@@ -67,6 +76,16 @@ fn main() {
             }
         });
 
+        // Handle the movement of the canvas when pressing the middle mouse button.
+        if let Some(Button::Mouse(MouseButton::Middle)) = e.press_args() {
+            canvas_follows_mouse = true;
+            println!("Canvas now follows the mouse");
+        }
+        if let Some(Button::Mouse(MouseButton::Middle)) = e.release_args() {
+            canvas_follows_mouse = false;
+            println!("Canvas no longer follows the mouse");
+        }
+
         // Handle drawing a rectangle or finishing the rectangle when clicking with the mouse.
         if let Some(Button::Mouse(MouseButton::Left)) = e.press_args() {
             if let Some(first_point) = starting_rect_point {
@@ -100,7 +119,12 @@ fn main() {
         window.draw_2d(&e, |c, g, _device| {
             clear([0.4, 0.2, 0., 1.], g);
 
-            grid.draw(&grid_line, &c.draw_state, c.transform, g);
+            grid.draw(
+                &grid_line,
+                &c.draw_state,
+                c.trans_pos(transform.translation_px()).transform,
+                g,
+            );
 
             // Draw all rectangles that are part of the map
             for &rect in &rectangles {
diff --git a/src/transform.rs b/src/transform.rs
index ef94029..a91d7da 100644
--- a/src/transform.rs
+++ b/src/transform.rs
@@ -121,6 +121,11 @@ impl Transform {
         }
     }
 
+    /// Move the canvas by the vector in pixels.
+    pub fn move_by_px(&mut self, by: [f64; 2]) {
+        self.translation_px = math::add(self.translation_px, by);
+    }
+
     pub fn pixels_per_m(&self) -> f64 {
         self.pixels_per_m
     }