Game Logic In C++

This step implements the rules of the game in C++.

Slint's general philosophy is that you implement the user interface in Slint and the business logic in your favorite programming language.

The game rules enforce that at most two tiles have their curtain open. If the tiles match, then the game considers them solved and they remain open. Otherwise, the game waits briefly so the player can memorize the location of the icons, and then closes the curtains again.

Add the following code inside the MainWindow component to signal to the C++ code when the user clicks on a tile.

    export component MainWindow inherits Window {
        width: 326px;
        height: 326px;

        callback check_if_pair_solved(); // Added
        in property <bool> disable_tiles; // Added

        in-out property <[TileData]> memory_tiles: [
           { image: @image-url("icons/at.png") },

This change adds a way for the MainWindow to call to the C++ code that it should check if a player has solved a pair of tiles. The Rust code needs an additional property to toggle to disable further tile interaction, to prevent the player from opening more tiles than allowed. No cheating allowed!

The last change to the code is to act when the MemoryTile signals that a player clicked it.

Add the following handler in the MainWindow for loop clicked handler:

        for tile[i] in memory_tiles : MemoryTile {
            x: mod(i, 4) * 74px;
            y: floor(i / 4) * 74px;
            width: 64px;
            height: 64px;
            icon: tile.image;
            open_curtain: tile.image_visible || tile.solved;
            // propagate the solved status from the model to the tile
            solved: tile.solved;
            clicked => {
                // old: tile.image_visible = !tile.image_visible;
                // new:
                if (!root.disable_tiles) {
                    tile.image_visible = !tile.image_visible;
                    root.check_if_pair_solved();
                }
            }
        }

On the C++ side, you can now add a handler to the check_if_pair_solved callback, that checks if a player opened two tiles. If they match, the code sets the solved property to true in the model. If they don't match, start a timer that closes the tiles after one second. While the timer is running, disable every tile so a player can't click anything during this time.

Insert this code before the main_window->run() call:

    main_window->on_check_if_pair_solved(
            [main_window_weak = slint::ComponentWeakHandle(main_window)] {
                auto main_window = *main_window_weak.lock();
                auto tiles_model = main_window->get_memory_tiles();
                int first_visible_index = -1;
                TileData first_visible_tile;
                for (int i = 0; i < tiles_model->row_count(); ++i) {
                    auto tile = *tiles_model->row_data(i);
                    if (!tile.image_visible || tile.solved)
                        continue;
                    if (first_visible_index == -1) {
                        first_visible_index = i;
                        first_visible_tile = tile;
                        continue;
                    }
                    bool is_pair_solved = tile == first_visible_tile;
                    if (is_pair_solved) {
                        first_visible_tile.solved = true;
                        tiles_model->set_row_data(first_visible_index,
                                                  first_visible_tile);
                        tile.solved = true;
                        tiles_model->set_row_data(i, tile);
                        return;
                    }
                    main_window->set_disable_tiles(true);

                    slint::Timer::single_shot(std::chrono::seconds(1),
                        [=]() mutable {
                            main_window->set_disable_tiles(false);
                            first_visible_tile.image_visible = false;
                            tiles_model->set_row_data(first_visible_index,
                                                      first_visible_tile);
                            tile.image_visible = false;
                            tiles_model->set_row_data(i, tile);
                        });
                }
            });

The code uses a ComponentWeakHandle pointer of the main_window. This is important because capturing a copy of the main_window itself within the callback handler would result in circular ownership. The MainWindow owns the callback handler, which itself owns a reference to the MainWindow, which must be weak instead of strong to avoid a memory leak.

These were the last changes and running the code opens a window that allows a player to play the game by the rules.