1 files changed, 7 insertions, 0 deletions
diff --git a/src/sandbox.cpp b/src/sandbox.cpp
index c6d0294..2c09d77 100644
--- a/src/sandbox.cpp
+++ b/src/sandbox.cpp
@@ -102,17 +102,24 @@ void Sandbox::simulate_step() {
     dirty_writeto = {};
     const auto [x0, y0] = dirty_curr.bl;
     const auto [x1, y1] = dirty_curr.tr;
+
     // Clear update bit for this cycle
     for (_y = y0; _y <= y1; ++_y) {
         for (_x = x0; _x <= x1; ++_x) {
             gs(_x, _y).updated = false;
         }
     }
+
+    // Update
     for (_y = y0; _y <= y1; ++_y) {
         for (_x = x0; _x <= x1; ++_x) {
             simulate_sand_tile(*this, _x, _y);
         }
     }
+    dirty_writeto.bl -= Pt(1, 1);
+    dirty_writeto.tr += Pt(1, 1);
+    dirty_writeto = rect_intersect(dirty_writeto, Rect(0, 0, width - 1, height - 1));
+
     ++ncycle;
 }