LibCards: Support "previewing" cards that may be covered by other cards

For example, in Solitaire, the vertical normal stacks cover the suit of
all but the topmost card in the stack. To see the suit of covered cards
the user currently has to move the cards on top of them out of the way.

This adds an API for games to set a card at a location to be previewed,
which will draw that card on top of all other cards without moving it.

Userland/Libraries/LibCards/Card.h

@@ -98,12 +98,14 @@ public:
     bool is_moving() const { return m_moving; }
     bool is_upside_down() const { return m_upside_down; }
     bool is_inverted() const { return m_inverted; }
+    bool is_previewed() const { return m_previewed; }
     Gfx::Color color() const { return (m_suit == Suit::Diamonds || m_suit == Suit::Hearts) ? Color::Red : Color::Black; }
 
     void set_position(const Gfx::IntPoint p) { m_rect.set_location(p); }
     void set_moving(bool moving) { m_moving = moving; }
     void set_upside_down(bool upside_down) { m_upside_down = upside_down; }
     void set_inverted(bool inverted) { m_inverted = inverted; }
+    void set_previewed(bool previewed) { m_previewed = previewed; }
 
     void save_old_position();
 
@@ -122,6 +124,7 @@ private:
     bool m_moving { false };
     bool m_upside_down { false };
     bool m_inverted { false };
+    bool m_previewed { false };
 };
 
 enum class Shuffle {

Userland/Libraries/LibCards/CardGame.cpp

@@ -144,4 +144,22 @@ void CardGame::set_background_color(Gfx::Color color)
     CardPainter::the().set_background_color(color);
 }
 
+void CardGame::preview_card(CardStack& stack, Gfx::IntPoint click_location)
+{
+    if (!stack.preview_card(click_location))
+        return;
+
+    m_previewed_card_stack = stack;
+    update(stack.bounding_box());
+}
+
+void CardGame::clear_card_preview()
+{
+    VERIFY(m_previewed_card_stack);
+
+    update(m_previewed_card_stack->bounding_box());
+    m_previewed_card_stack->clear_card_preview();
+    m_previewed_card_stack = nullptr;
+}
+
 }

Userland/Libraries/LibCards/CardGame.h

@@ -41,6 +41,10 @@ public:
     void drop_cards_on_stack(CardStack&, CardStack::MovementRule);
     void clear_moving_cards();
 
+    bool is_previewing_card() const { return !m_previewed_card_stack.is_null(); }
+    void preview_card(CardStack&, Gfx::IntPoint click_location);
+    void clear_card_preview();
+
     void dump_layout() const;
 
 protected:
@@ -53,6 +57,7 @@ private:
 
     NonnullRefPtrVector<Card> m_moving_cards;
     RefPtr<CardStack> m_moving_cards_source_stack;
+    RefPtr<CardStack> m_previewed_card_stack;
 };
 
 }

Userland/Libraries/LibCards/CardStack.cpp

@@ -93,12 +93,23 @@ void CardStack::paint(GUI::Painter& painter, Gfx::Color background_color)
         return;
     }
 
+    RefPtr<Card> previewed_card;
+
     for (size_t i = 0; i < m_stack.size(); ++i) {
         if (auto& card = m_stack[i]; !card.is_moving()) {
+            if (card.is_previewed()) {
+                VERIFY(!previewed_card);
+                previewed_card = card;
+                continue;
+            }
+
             auto highlighted = m_highlighted && (i == m_stack.size() - 1);
             card.clear_and_paint(painter, Gfx::Color::Transparent, highlighted);
         }
     }
+
+    if (previewed_card)
+        previewed_card->clear_and_paint(painter, Gfx::Color::Transparent, false);
 }
 
 void CardStack::rebound_cards()
@@ -239,6 +250,32 @@ bool CardStack::is_allowed_to_push(Card const& card, size_t stack_size, Movement
     return true;
 }
 
+bool CardStack::preview_card(Gfx::IntPoint click_location)
+{
+    RefPtr<Card> last_intersect;
+
+    for (auto& card : m_stack) {
+        if (!card.rect().contains(click_location))
+            continue;
+        if (card.is_upside_down())
+            continue;
+
+        last_intersect = card;
+    }
+
+    if (!last_intersect)
+        return false;
+
+    last_intersect->set_previewed(true);
+    return true;
+}
+
+void CardStack::clear_card_preview()
+{
+    for (auto& card : m_stack)
+        card.set_previewed(false);
+}
+
 bool CardStack::make_top_card_visible()
 {
     if (is_empty())

Userland/Libraries/LibCards/CardStack.h

@@ -50,6 +50,10 @@ public:
 
     bool is_allowed_to_push(Card const&, size_t stack_size = 1, MovementRule movement_rule = MovementRule::Alternating) const;
     void add_all_grabbed_cards(Gfx::IntPoint click_location, NonnullRefPtrVector<Card>& grabbed, MovementRule movement_rule = MovementRule::Alternating);
+
+    bool preview_card(Gfx::IntPoint click_location);
+    void clear_card_preview();
+
     void paint(GUI::Painter&, Gfx::Color background_color);
     void clear();