drawing the game 

This is enough information to start drawing the game better.

  def onPaint(g: Graphics2D) {
    val view = ui.view

    def buildRect(pos: (Int, Int)): Rectangle =
      new Rectangle(pos._1 * (blockSize + blockMargin),
        (view.gridSize._2 - pos._2 - 1) * (blockSize + blockMargin),
        blockSize, blockSize)
    def drawEmptyGrid {
      g setColor bluishLigherGray
      for {
        x <- 0 to view.gridSize._1 - 1
        y <- 0 to view.gridSize._2 - 2
        val pos = (x, y)
      } g draw buildRect(pos)      
    }
    def drawBlocks {
      g setColor bluishEvenLigher
      view.blocks foreach { b => g fill buildRect(b.pos) }
    }
    def drawCurrent {
      g setColor bluishSilver
      view.current foreach { b => g fill buildRect(b.pos) }
    }
    drawEmptyGrid
    drawBlocks
    drawCurrent
  }

Now that we have a way to visualize the game state, we should implement some moves.

stage 

We need a better way of representing the current piece besides a sequence of blocks. A Piece class should keep the current position in (Double, Double) and calculate the current from the local coordinate system.

case class Piece(pos: (Double, Double), kind: PieceKind, locals: Seq[(Double, Double)]) {
  def current: Seq[Block] =
    locals map { case (x, y) => 
      Block((math.floor(x + pos._1).toInt, math.floor(y + pos._2).toInt), kind)
    }
}
case object Piece {
  def apply(pos: (Double, Double), kind: PieceKind): Piece =
    kind match {
      case TKind => Piece(pos, kind, Seq((-1.0, 0.0), (0.0, 0.0), (1.0, 0.0), (0.0, 1.0)))
    }
}

This allows us to define Stage which enforces the physics within the game world.

package com.eed3si9n.tetrix

class Stage(size: (Int, Int)) {
  private[this] def dropOffPos = (size._1 / 2.0, size._2 - 3.0)
  private[this] var currentPiece = Piece(dropOffPos, TKind)
  private[this] var blocks = Block((0, 0), TKind) +: currentPiece.current
  def view: GameView = GameView(blocks, size, currentPiece.current)
}

To move the current piece, it is unloaded from the grid, moved to a new position, and then reloaded back in.

Here’s the moveBy for Piece class:

  def moveBy(delta: (Double, Double)): Piece =
    copy(pos = (pos._1 + delta._1, pos._2 + delta._2))

and here’s the unloading and loading:

class Stage(size: (Int, Int)) {
  ...

  def moveLeft() = moveBy(-1.0, 0.0)
  def moveRight() = moveBy(1.0, 0.0)
  private[this] def moveBy(delta: (Double, Double)): this.type = {
    val unloaded = unload(currentPiece, blocks)
    val moved = currentPiece.moveBy(delta)
    blocks = load(moved, unloaded)
    currentPiece = moved
    this
  }
  private[this] def unload(p: Piece, bs: Seq[Block]): Seq[Block] = {
    val currentPoss = p.current map {_.pos}
    bs filterNot { currentPoss contains _.pos  }
  }
  private[this] def load(p: Piece, bs: Seq[Block]): Seq[Block] =
    bs ++ p.current
}

wiring it up 

Let’s wire the stage up to the abstract UI:

package com.eed3si9n.tetrix

class AbstractUI {
  private[this] val stage = new Stage((10, 20))
  def left() {
    stage.moveLeft()
  }
  def right() {
    stage.moveRight()
  }
  def up() {
  }
  def down() {
  }
  def space() {
  }
  def view: GameView = stage.view
}

You should be able run swing UI and see the piece move.