Android UI

Having an algorithm to calculate the next step of a game is nice, but we need a UI in order to show the game playing.

We start with the Android implementation. We create a custom view which draws a gray rectangle for each living cell.

class BoardView : View {

    private val paint = Paint().apply {
        color = Color.GRAY
        style = Paint.Style.FILL
        strokeWidth = 0.0f
    }

…

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        val board = board ?: return

        for (rowIdx in 0 until board.rows) {
            for (columnIdx in 0 until board.columns) {
                if (board.cellAt(column = columnIdx, row = rowIdx).alive) {
                    canvas.drawRect(rectFor(rowIdx, columnIdx), paint)
                }
            }
        }
    }

    private fun rectFor(rowIdx: Int, columnIdx: Int): RectF {
        val left = (columnIdx * cellSize) + cellPadding
        val right = (left + cellSize) - cellPadding
        val top = (rowIdx * cellSize) + cellPadding
        val bottom = (top + cellSize) - cellPadding
        return RectF(left, top, right, bottom)
    }
}

The main activity uses a timer as a game loop and calculates a new step every half a second and then updates the UI drawing the new board.

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContentView(R.layout.activity_main)

        val columns = 30
        val rows = 50
        val board = Board(columns, rows)
        board.setCells(
            """
                ***_*
                *____
                ___**
                _**_*
                *_*_*
                """.trimIndent().cells().translatedTo(columns / 2 - 2, rows / 2 - 2))


        boardView.cellSize = 14.0f * resources.displayMetrics.density
        boardView.board = board

        fixedRateTimer("GameLoop", false, period = 500L) {
            board.calculateNextGeneration()
            boardView.invalidate()
        }
    }
}

Android UI