In the second assignment, you will implement another classic computer game, namely Tetris. The game of Tetris centers around tetrominoes: geometric shapes of 4 orthogonally connected squares. If you are not familiar with the game, you can play an official web version here

You are making a slightly simplified version of this game:

• No “ghost” of where the current tetromino will end up.
• No scoring.
• No difficulty curve (speeding up).
• No hold functionality.
• No box showing the next tetrominoes.
• In the official Tetris, if a tetromino is rotated but the target spot is occupied or out of bounds, the tetromino may slightly be moved to a space that is free via a “wall-kick" system. We do not implement this, we simply do not rotate if the target spot is occupied or out of bounds.

The assignment is similar to assignments 2.1 and 2.3. Keep your code as simple and readable as possible. If your implementation is more than 450 lines long (including empty lines), then something is probably wrong. The reference implementation is 170 lines long.

The framework is highly similar to the snake framework. Code to draw the game state and handle keyboard events has already been provided in src/tetris/game/TetrisGame.scala, where you can also run the game (press the play button). You only have to implement the game logic. Your implementation should go in src/tetris/logic/TetrisLogic.scala . If you want to add additional files, please make certain to keep them in the src.tetris.logic package (that is the directory src/tetris/logic).

The drawing and event code, TetrisGame interacts with the game logic TetrisLogic as follows:

• When drawing the game, TetrisGame asks TetrisLogic for each cell in the grid what the type is. The cell types are defined tetris.logic.CellType and are either Empty or an <X>Cell where X is the letter corresponding to the tetromino that the block originated from. See below for a list of tetrominoes. The drawing code also calls isGameOver and draws a game over text if this is true.
• When the user presses the left, right or down arrow key, then moveLeft, moveRight or moveDown is called correspondingly.
• When the user presses the s key or the up arrow, then rotateRight is called. When the user pressed a then rotateLeft is called.
• When the user presses the space bar, then doHardDrop is called. This immediately drops the current tetromino to where it is supported by the floor or already placed blocks.
• Every 5 seconds (by default) the method moveDown is called to advance the game. You can adjust the speed of the game by increasing or decreasing the value TetrisLogic.FramesPerSecond.

The test setup is very similar to the Snake test setup. There are two main differences:

• In Snake after each test frame Step is called, this is not true for Tetris: only the actions that are listed for the test frame (such as Left, Right, Down, RotateRight, etc.) are called.
• Some Tetris tests provide an initial configuration of the board.

To ensure reproducible behavior, we specify exactly how a random number generator must be used to generate random tetrominoes. Similar to snake, a random number generator is passed to the TetrisLogic class as an argument called randomGen. You should call randomInt(nrTetrominoes), where nrTetrominoes=7, to determine the index of the tetromino to get.

The tetrominoes should be placed based on their anchor, which is located:

• at the center of rotation (shown as a circle above) for tetrominoes J, L, S, T and Z.
• at the star for tetrominoes I and O.

The initial position of the anchor of the tetromino is on the second row, in the middle column (rounded down to the left in case of an even number of columns). The initial orientation of the tetromino is the leftmost orientation in the table above.

For this exercise, you have to implement how the pieces are anchored and how they rotate as shown in the table above. You are allowed to hard-code this, but this gives fewer points than doing it in a more elegant way.

You can represent a tetromino as a set of four points relative to the center of rotation/anchor. For example the J-tetromino is then (-1,-1),(-1,0),(0,0),(1,0) (y-axis increases downwards). Rotating clockwise by 90-degree angles means that each point (x,y), becomes (-y,x). For example, the 90-degree rotated form of the J-tetromino is then (1,-1),(0,-1),(0,0),(0,1) Rotating counter-clockwise by 90-degree angles means that each point (x,y) becomes (y,-x).

This works nicely, except for the O and I tetrominoes. For the O tetromino, it is easiest to simply implement rotation by doing nothing.

For the I tetromino, one way is to implement the tetromino as a set of four points relative to the anchor (star in the picture), not relative to the center of rotation (circle in the picture). The positions are then (-1,0),(0,0),(1,0),(2,0). Rotating clockwise as described above ((x,y) -> (-y,x)) works, but the tetromino always ends up one position to the left of where it should be (i.e. (0,-1),(0,0),(0,1),(0,2)). We can fix this by pushing the tetromino one to the right after rotation. In other words, we do (x,y) -> (-y + 1,x). Rotating counter-clockwise works by rotating around the anchor and then pushing one position to the down, (x,y) -> (y ,-x + 1). Note: Anchors do not rotate, they stay put!

Hence, there are three rotation behaviors:

• Rotation for pieces where the anchor=the center of rotation ((x,y) -> (-y,x)) (J,L,S,T,Z)
• Rotation of the O-tetromino (rotation is a no-op)
• Rotation of the I-tetromino ((x,y) -> (-y + 1,x))

To get full points, make an abstract class Tetromino with abstract functions rotateLeft and rotateRight. This class should have three subclasses, each implementing a different rotation behavior.

There are 2 assignments for tetris:

Implement the basics of tetris: piece rotation and movement. This assignment is pass/fail. To pass this assignment, you need to pass 17 tests from TetrisTestSuite3_1.

Implement full tetris. Tests can be found in TetrisTestSuite3_2

Grading is built up as follows:

• Amount of tests passed: 5.5 points
• Use of immutable gamestate: 1.0 points (see below)
• Meaningful usage of higher order functions (0.75 points)
  • Meaningful usage of map: 0.25 points. NOTE: This means the map higher order function, Not the Map datastructure. No point will be given for using the map datastructure instead of the higher order function.
  • Meaningful usage of filter: 0.25 points
  • Meaningful usage of exists or forall: 0.25 points
• Implementation of rotation and anchors (see table above) (max 0.75 points):
  • Hard coding is allowed, but gives 0.0 points
  • Not hard coded, but does not use subclassing (described above) (0.4 points)
  • Implement tetrominoes by using subclasses (see above) (0.75 points)
• Code style: 2 points

Total : 10 points

In contrast to snake, no points are subtracted for using a 2 dimensional structure, and using such a structure is encouraged.

These rewards are intended to reward trying out new styles of programming.

An example of an immutable game state can be found in the Sokoban example in the immutable sokoban logic class. To get the full 1.0 point, you need to:

• Not use mutable containers (Arrays and others)
• Use a GameState that contains only vals
• Use a var only to keep track of the current game state CHANGE FROM SNAKE: You are NOT allowed to locally use vars and builders inside functions to get the immutability bonus.

Code style is judged as described in the readable code lectures and the code style grading guidelines.