PaintBrush: Speed up the bucket tool with smarter use of Vector.

Put together a pretty well-performing queue using a Vector and an offset.
By using the new Vector::shift_left(int) instead of Vector::take_first()
we can avoid shifting the vector contents every time and instead only
do it every so often.

Maybe this could be generalized into a separate class, I'm not sure if it's
the best algorithm though, it's just what I came up with right now. :^)

AK/Vector.h

@@ -298,6 +298,19 @@ public:
         m_capacity = new_capacity;
     }
 
+    void shift_left(int count)
+    {
+        ASSERT(count <= m_size);
+        if (count == m_size) {
+            clear();
+            return;
+        }
+        for (int i = 0; i < m_size - count; ++i) {
+            at(i) = move(at(i + count));
+        }
+        m_size -= count;
+    }
+
     void resize(int new_size)
     {
         if (new_size == size())

Applications/PaintBrush/BucketTool.cpp

@@ -15,21 +15,34 @@ BucketTool::~BucketTool()
 
 static void flood_fill(GraphicsBitmap& bitmap, const Point& start_position, Color target_color, Color fill_color)
 {
-    SinglyLinkedList<Point> queue;
+    Vector<Point> queue;
+    queue.append(start_position);
+    int queue_pos = 0;
+    while (queue_pos != queue.size()) {
+        auto position = queue[queue_pos++];
+
+        if (queue_pos > 4096) {
+            queue.shift_left(4096);
+            queue_pos = 0;
+        }
 
-    queue.append(Point(start_position));
-    while (!queue.is_empty()) {
-        auto position = queue.take_first();
         if (!bitmap.rect().contains(position))
             continue;
         if (bitmap.get_pixel(position) != target_color)
             continue;
         bitmap.set_pixel(position, fill_color);
 
-        queue.append(position.translated(0, -1));
-        queue.append(position.translated(0, 1));
-        queue.append(position.translated(1, 0));
-        queue.append(position.translated(-1, 0));
+        if (position.x() != 0)
+            queue.append(position.translated(0, -1));
+
+        if (position.x() != bitmap.width() - 1)
+            queue.append(position.translated(0, 1));
+
+        if (position.y() != 0)
+            queue.append(position.translated(-1, 0));
+
+        if (position.y() != bitmap.height() - 1)
+            queue.append(position.translated(1, 0));
     }
 }