unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls;

type
  TForm1 = class(TForm)
    Timer1: TTimer;
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;


const

shapes :array[0..6] of array[0..3,0..3] of byte =

(
  (
  (0,0,0,0),
  (0,0,0,0),
  (1,1,1,1),
  (0,0,0,0)
  ),
  (
  (0,0,0,0),
  (0,1,0,0),
  (0,1,1,1),
  (0,0,0,0)
  ),
  (
  (0,0,0,0),
  (0,0,0,1),
  (0,1,1,1),
  (0,0,0,0)
  ),
  (
  (0,0,0,0),
  (0,1,1,0),
  (0,1,1,0),
  (0,0,0,0)
  ),
  (
  (0,0,0,0),
  (1,1,0,0),
  (0,1,1,0),
  (0,0,0,0)
  ),
  (
  (0,0,0,0),
  (0,0,1,1),
  (0,1,1,0),
  (0,0,0,0)
  ),
  (
  (0,0,0,0),
  (0,1,0,0),
  (1,1,1,0),
  (0,0,0,0)
  )
);


bricksize=16;
playwidth=10;
playheight=20;
playwidthpx=bricksize*playwidth;
playheightpx=bricksize*playheight;

type

  TTetromino= record
    typ: integer;
    x:    integer;
    y:    integer;
    color: TColor;
  end;

var
  vscreen: TBitmap;
  playfield: array[0..playheight-1, 0..playwidth-1] of byte;

  tetromino: TTetromino;

implementation

{$R *.dfm}


procedure PaintBrick(x,y:integer; color: TColor=clRed);
begin
  if (x>=0)and(y>=0)and(x<playwidth)and(y<playheight) then
  begin
    vscreen.Canvas.Brush.Color:=color;
    vscreen.Canvas.FillRect(Rect(x*bricksize,y*bricksize,(x+1)*bricksize,(y+1)*bricksize));
  end;
end;

procedure PaintPlayField();
var
  i,j:integer;
begin
  vscreen.Canvas.Brush.Color:=clBlack;
  vscreen.Canvas.FillRect(Rect(0,0,playwidthpx,playheightpx));

  for i:=0 to playheight-1 do
  for j:=0 to playwidth-1 do
    if playfield[i,j]>0 then
      PaintBrick(j,i);

  for i:=0 to 3 do
  for j:=0 to 3 do
    if shapes[tetromino.typ][i,j]<>0 then
      PaintBrick(tetromino.x+j,tetromino.y+i,clBlue);
end;


procedure NewTetromino();
begin
  tetromino.typ:=random(7);
  tetromino.y:=-4;
  tetromino.x:=playwidth div 2 - 2;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  vscreen:=TBitmap.Create;
  vscreen.Width:=playwidthpx;
  vscreen.Height:=playheightpx;
  Randomize();
  NewTetromino();
  Paint();
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  PaintPlayField;
  Form1.Canvas.Draw(0,0,vscreen);
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  inc(tetromino.y);
  if tetromino.y=playheight then NewTetromino();
  Form1.Repaint;
end;

end.