Snake: Try to only repaint the parts that actually changed between ticks.

Games/Snake/SnakeGame.cpp

@@ -7,6 +7,7 @@
 SnakeGame::SnakeGame(GWidget* parent)
     : GWidget(parent)
 {
+    set_font(Font::default_bold_font());
     m_fruit_bitmap = GraphicsBitmap::load_from_file("/res/icons/snake/paprika.png");
     srand(time(nullptr));
     reset();
@@ -22,10 +23,12 @@ void SnakeGame::reset()
     m_tail.clear_with_capacity();
     m_length = 2;
     m_score = 0;
+    m_score_text = "Score: 0";
     m_velocity_queue.clear();
     stop_timer();
     start_timer(120);
     spawn_fruit();
+    update();
 }
 
 bool SnakeGame::is_available(const Coordinate& coord)
@@ -53,16 +56,28 @@ void SnakeGame::spawn_fruit()
     m_fruit = coord;
 }
 
+Rect SnakeGame::score_rect() const
+{
+    int score_width = font().width(m_score_text);
+    return { width() - score_width - 2, height() - font().glyph_height() - 2, score_width, font().glyph_height() };
+}
+
 void SnakeGame::timer_event(CTimerEvent&)
 {
+    Vector<Coordinate> dirty_cells;
+
     m_tail.prepend(m_head);
 
-    if (m_tail.size() > m_length)
+    if (m_tail.size() > m_length) {
+        dirty_cells.append(m_tail.last());
         m_tail.take_last();
+    }
 
     if (!m_velocity_queue.is_empty())
         m_velocity = m_velocity_queue.dequeue();
 
+    dirty_cells.append(m_head);
+
     m_head.row += m_velocity.vertical;
     m_head.column += m_velocity.horizontal;
 
@@ -77,6 +92,8 @@ void SnakeGame::timer_event(CTimerEvent&)
     if (m_head.column < 0)
         m_head.column = m_columns - 1;
 
+    dirty_cells.append(m_head);
+
     for (int i = 0; i < m_tail.size(); ++i) {
         if (m_head == m_tail[i]) {
             game_over();
@@ -87,9 +104,16 @@ void SnakeGame::timer_event(CTimerEvent&)
     if (m_head == m_fruit) {
         ++m_length;
         ++m_score;
+        m_score_text = String::format("Score: %u", m_score);
+        update(score_rect());
+        dirty_cells.append(m_fruit);
         spawn_fruit();
+        dirty_cells.append(m_fruit);
+    }
+
+    for (auto& coord : dirty_cells) {
+        update(cell_rect(coord));
     }
-    update();
 }
 
 void SnakeGame::keydown_event(GKeyEvent& event)
@@ -124,22 +148,23 @@ void SnakeGame::keydown_event(GKeyEvent& event)
     }
 }
 
-void SnakeGame::paint_event(GPaintEvent& event)
+Rect SnakeGame::cell_rect(const Coordinate& coord) const
 {
-    GPainter painter(*this);
-    painter.fill_rect(event.rect(), Color::Black);
-
     auto game_rect = rect();
     auto cell_size = Size(game_rect.width() / m_columns, game_rect.height() / m_rows);
-
-    auto cell_rect = [&] (const Coordinate& coord) -> Rect {
     return {
         coord.column * cell_size.width(),
         coord.row * cell_size.height(),
         cell_size.width(),
         cell_size.height()
     };
-    };
+}
+
+void SnakeGame::paint_event(GPaintEvent& event)
+{
+    GPainter painter(*this);
+    painter.add_clip_rect(event.rect());
+    painter.fill_rect(event.rect(), Color::Black);
 
     painter.fill_rect(cell_rect(m_head), Color::Yellow);
     for (auto& coord : m_tail)
@@ -147,7 +172,7 @@ void SnakeGame::paint_event(GPaintEvent& event)
 
     painter.draw_scaled_bitmap(cell_rect(m_fruit), *m_fruit_bitmap, m_fruit_bitmap->rect());
 
-    painter.draw_text(rect(), String::format("Score: %u", m_score), TextAlignment::TopLeft, Color::White);
+    painter.draw_text(score_rect(), m_score_text, TextAlignment::TopLeft, Color::White);
 }
 
 void SnakeGame::game_over()

Games/Snake/SnakeGame.h

@@ -35,6 +35,8 @@ private:
     bool is_available(const Coordinate&);
     void queue_velocity(int v, int h);
     const Velocity& last_velocity() const;
+    Rect cell_rect(const Coordinate&) const;
+    Rect score_rect() const;
 
     int m_rows { 20 };
     int m_columns { 20 };
@@ -51,6 +53,7 @@ private:
 
     int m_length { 0 };
     unsigned m_score { 0 };
+    String m_score_text;
 
     RetainPtr<GraphicsBitmap> m_fruit_bitmap;
 };