Snap rooms to the grid

2 files changed, 28 insertions, 2 deletions

diff --git a/src/math.rs b/src/math.rs
index c4e7ac0..60a53e8 100644
--- a/src/math.rs
+++ b/src/math.rs
@@ -16,3 +16,21 @@ pub fn bounding_rect(pos1: Vector2, pos2: Vector2) -> Rectangle {
         height: max_y - min_y,
     }
 }
+
+/// Round a floating point number to the nearest step given by the step argument. For instance, if
+/// the step is 0.5, then all numbers from 0.0 to 0.24999... will be 0., while all numbers from
+/// 0.25 to 0.74999... will be 0.5 and so on.
+pub fn round(num: f32, step: f32) -> f32 {
+    // Only positive steps will be accepted.
+    assert!(step > 0.);
+
+    let lower_bound = ((num / step) as i32) as f32 * step;
+    let upper_bound = lower_bound + step;
+
+    // Compare the distances and prefer the smaller. If they are the same, prefer the upper bound.
+    if (num - lower_bound) < (upper_bound - num) {
+        lower_bound
+    } else {
+        upper_bound
+    }
+}
diff --git a/src/tool/room_tool.rs b/src/tool/room_tool.rs
index 8288c97..6a9ad55 100644
--- a/src/tool/room_tool.rs
+++ b/src/tool/room_tool.rs
@@ -29,7 +29,11 @@ impl Tool for RoomTool {
         let mouse_pos_m = transform.point_px_to_m(rl.get_mouse_position());
         // Update the currently drawn rectangle, if it exists
         if let Some((_, ref mut pos2)) = &mut self.unfinished_rect {
-            *pos2 = mouse_pos_m;
+            let snapped_mouse_pos = Vector2::new(
+                math::round(mouse_pos_m.x, 0.5),
+                math::round(mouse_pos_m.y, 0.5),
+            );
+            *pos2 = snapped_mouse_pos;
         }
 
         // Start or finish drawing the currently unfinished rectangle
@@ -38,7 +42,11 @@ impl Tool for RoomTool {
                 self.room_rects.push(math::bounding_rect(pos1, pos2));
                 self.unfinished_rect = None;
             } else {
-                self.unfinished_rect = Some((mouse_pos_m, mouse_pos_m))
+                let snapped_mouse_pos = Vector2::new(
+                    math::round(mouse_pos_m.x, 0.5),
+                    math::round(mouse_pos_m.y, 0.5),
+                );
+                self.unfinished_rect = Some((snapped_mouse_pos, snapped_mouse_pos))
             }
         }