Game Logic In JavaScript - Slint Memory Game Tutorial (node)

# Game Logic In JavaScript

We'll implement the rules of the game in JavaScript as well. The general philosophy of Slint is that merely the user interface is implemented in the `.slint` language and the business logic in your favorite programming language. The game rules shall enforce that at most two tiles have their curtain open. If the tiles match, then we consider them solved and they remain open. Otherwise we wait for a little while, so the player can memorize the location of the icons, and then close them again.

We'll modify the `.slint` markup in the `memory.slint` file to signal to the JavaScript code when the user clicks on a tile. Two changes to MainWindow are needed: We need to add a way for the MainWindow to call to the JavaScript code that it should check if a pair of tiles has been solved. And we need to add a property that JavaScript code can toggle to disable further tile interaction, to prevent the player from opening more tiles than allowed. No cheating allowed! First, we paste the callback and property declarations into MainWindow:

        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") },

The last change to the `.slint` markup is to act when the MemoryTile signals that it was clicked on. We add the following handler in MainWindow:

            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 JavaScript side, we can now add an handler to the `check_if_pair_solved` callback, that will check if two tiles are opened. If they match, the `solved` property is set to true in the model. If they don't match, start a timer that will close them after one second. While the timer is running, we disable every tile so one can't click anything during this time.

Insert this code before the `mainWindow.run()` call:

    let model = new slint.ArrayModel(tiles);
    mainWindow.memory_tiles = model;

    mainWindow.check_if_pair_solved = function () {
        let flipped_tiles = [];
        tiles.forEach((tile, index) => {
            if (tile.image_visible && !tile.solved) {
                flipped_tiles.push({
                    index,
                    tile
                });
            }
        });

        if (flipped_tiles.length == 2) {
            let {
                tile: tile1,
                index: tile1_index
            } = flipped_tiles[0];

            let {
                tile: tile2,
                index: tile2_index
            } = flipped_tiles[1];

            let is_pair_solved = tile1.image.path === tile2.image.path;
            if (is_pair_solved) {
                tile1.solved = true;
                model.setRowData(tile1_index, tile1);
                tile2.solved = true;
                model.setRowData(tile2_index, tile2);
            } else {
                mainWindow.disable_tiles = true;
                setTimeout(() => {
                    mainWindow.disable_tiles = false;
                    tile1.image_visible = false;
                    model.setRowData(tile1_index, tile1);
                    tile2.image_visible = false;
                    model.setRowData(tile2_index, tile2);
                }, 1000)

            }
        }
    };

    mainWindow.run();

These were the last changes and running the result gives us a window on the screen that allows us to play the game by the rules.