Subsections


1. The CRT unit.

crtex This chapter describes the CRT unit for Free Pascal, both under DOS LINUX and WINDOWS. The unit was first written for DOS by Florian klämpfl. The unit was ported to LINUX by Mark May1.1, and enhanced by Michaël Van Canneyt and Peter Vreman. It works on the LINUX console, and in xterm and rxvt windows under X-Windows. The functionality for both is the same, except that under LINUX the use of an early implementation (versions 0.9.1 and earlier of the compiler) the crt unit automatically cleared the screen at program startup. This chapter is divided in two sections.

1.1 Types, Variables, Constants

Color definitions :
  Black = 0;
  Blue = 1;
  Green = 2;
  Cyan = 3;
  Red = 4;
  Magenta = 5;
  Brown = 6;
  LightGray = 7;
  DarkGray = 8;
  LightBlue = 9;
  LightGreen = 10;
  LightCyan = 11;
  LightRed = 12;
  LightMagenta = 13;
  Yellow = 14;
  White = 15;
  Blink = 128;
Miscellaneous constants
  TextAttr: Byte = $07;
  TextChar: Char = ' ';
  CheckBreak: Boolean = True;
  CheckEOF: Boolean = False;
  CheckSnow: Boolean = False;
  DirectVideo: Boolean = False;
  LastMode: Word = 3;
  WindMin: Word = $0;
  WindMax: Word = $184f;
  ScreenWidth = 80;
  ScreenHeight = 25;
Some variables for compatibility with Turbo Pascal. However, they're not used by Free Pascal.
var
  checkbreak : boolean;
  checkeof : boolean;
  checksnow : boolean;
The following constants define screen modes on a DOS system:
Const
  bw40 = 0;
  co40 = 1;
  bw80 = 2;
  co80 = 3;
  mono = 7;
The TextAttr variable controls the attributes with which characters are written to screen.
var TextAttr : byte;
The DirectVideo variable controls the writing to the screen. If it is True, the the cursor is set via direct port access. If False, then the BIOS is used. This is defined under DOS only.
var DirectVideo : Boolean;
The Lastmode variable tells you which mode was last selected for the screen. It is defined on DOS only.
var lastmode : Word;

1.2 Procedures and Functions


1.2.1 AssignCrt

Declaration
Procedure AssignCrt (Var F: Text);
Description
AssignCrt Assigns a file F to the console. Everything written to the file F goes to the console instead. If the console contains a window, everything is written to the window instead.

Errors
None.
See also
Window

Example
Program Example1;
uses Crt;

{ Program to demonstrate the AssignCrt function. }

var
  F : Text;
begin
  AssignCrt(F);
  Rewrite(F); { Don't forget to open for output! }
  WriteLn(F,'This is written to the Assigned File');
  Close(F);
end.


1.2.2 CursorBig

Declaration
Procedure CursorBig ;
Description
Makes the cursor a big rectangle. Not implemented on LINUX.
Errors
None.
See also
CursorOn, CursorOff


1.2.3 ClrEol

Declaration
Procedure ClrEol ;
Description
ClrEol clears the current line, starting from the cursor position, to the end of the window. The cursor doesn't move
Errors
None.
See also
DelLine, InsLine, ClrScr

Example
Program Example9;
uses Crt;

{ Program to demonstrate the ClrEol function. }

begin
  Write('This line will be cleared from the',
        ' cursor postion until the right of the screen');
  GotoXY(27,WhereY);
  ReadKey;
  ClrEol;
  WriteLn;
end.


1.2.4 ClrScr

Declaration
Procedure ClrScr ;
Description
ClrScr clears the current window (using the current colors), and sets the cursor in the top left corner of the current window.
Errors
None.
See also
Window

Example
Program Example8;
uses Crt;

{ Program to demonstrate the ClrScr function. }

begin
  Writeln('Press any key to clear the screen');
  ReadKey;
  ClrScr;
  Writeln('Have fun with the cleared screen');
end.


1.2.5 CursorOff

Declaration
Procedure CursorOff ;
Description
Switches the cursor off (i.e. the cursor is no longer visible). Not implemented on LINUX.
Errors
None.
See also
CursorOn, CursorBig


1.2.6 CursorOn

Declaration
Procedure CursorOn ;
Description
Switches the cursor on. Not implemented on LINUX.
Errors
None.
See also
CursorBig, CursorOff


1.2.7 Delay

Declaration
Procedure Delay (DTime: Word);
Description
Delay waits a specified number of milliseconds. The number of specified seconds is an approximation, and may be off a lot, if system load is high.
Errors
None
See also
Sound, NoSound

Example
Program Example15;
uses Crt;

{ Program to demonstrate the Delay function. }
var
  i : longint;
begin
  WriteLn('Counting Down');
  for i:=10 downto 1 do
   begin
     WriteLn(i);
     Delay(1000); {Wait one second}
   end;     
  WriteLn('BOOM!!!'); 
end.


1.2.8 DelLine

Declaration
Procedure DelLine ;
Description
DelLine removes the current line. Lines following the current line are scrolled 1 line up, and an empty line is inserted at the bottom of the current window. The cursor doesn't move.
Errors
None.
See also
ClrEol, InsLine, ClrScr

Example
Program Example10;
uses Crt;

{ Program to demonstrate the InsLine function. }

begin
  ClrScr;
  WriteLn;
  WriteLn('Line 1');
  WriteLn('Line 2');
  WriteLn('Line 2');
  WriteLn('Line 3');
  WriteLn;
  WriteLn('Oops, Line 2 is listed twice,',
          ' let''s delete the line at the cursor postion');
  GotoXY(1,3);
  ReadKey;
  DelLine;
  GotoXY(1,10);
end.


1.2.9 GotoXY

Declaration
Procedure GotoXY (X: Byte; Y: Byte);
Description
Positions the cursor at (X,Y), X in horizontal, Y in vertical direction relative to the origin of the current window. The origin is located at (1,1), the upper-left corner of the window.

Errors
None.
See also
WhereX, WhereY, Window

Example
Program Example6;
uses Crt;

{ Program to demonstrate the GotoXY function. }

begin
  ClrScr;
  GotoXY(10,10);
  Write('10,10');
  GotoXY(70,20);
  Write('70,20');
  GotoXY(1,22);
end.


1.2.10 HighVideo

Declaration
Procedure HighVideo ;
Description
HighVideo switches the output to highlighted text. (It sets the high intensity bit of the video attribute)

Errors
None.
See also
TextColor, TextBackground, LowVideo, NormVideo

Example
Program Example14;
uses Crt;

{ Program to demonstrate the LowVideo, HighVideo, NormVideo functions. }

begin
  LowVideo;
  WriteLn('This is written with LowVideo');
  HighVideo;
  WriteLn('This is written with HighVideo');
  NormVideo;
  WriteLn('This is written with NormVideo');
end.


1.2.11 InsLine

Declaration
Procedure InsLine ;
Description
InsLine inserts an empty line at the current cursor position. Lines following the current line are scrolled 1 line down, causing the last line to disappear from the window. The cursor doesn't move.
Errors
None.
See also
ClrEol, DelLine, ClrScr

Example
Program Example10;
uses Crt;

{ Program to demonstrate the InsLine function. }

begin
  ClrScr;
  WriteLn;
  WriteLn('Line 1');
  WriteLn('Line 3');
  WriteLn;
  WriteLn('Oops, forgot Line 2, let''s insert at the cursor postion');
  GotoXY(1,3);
  ReadKey;
  InsLine;
  Write('Line 2');
  GotoXY(1,10);
end.


1.2.12 KeyPressed

Declaration
Function KeyPressed : Boolean;
Description
The Keypressed function scans the keyboard buffer and sees if a key has been pressed. If this is the case, True is returned. If not, False is returned. The Shift, Alt, Ctrl keys are not reported. The key is not removed from the buffer, and can hence still be read after the KeyPressed function has been called.

Errors
None.
See also
ReadKey

Example
Program Example2;
uses Crt;

{ Program to demonstrate the KeyPressed function. }

begin
  WriteLn('Waiting until a key is pressed');
  repeat
  until KeyPressed;
 { The key is not Read, 
   so it should also be outputted at the commandline}
end.


1.2.13 LowVideo

Declaration
Procedure LowVideo ;
Description
LowVideo switches the output to non-highlighted text. (It clears the high intensity bit of the video attribute)

Errors
None.
See also
TextColor, TextBackground, HighVideo, NormVideo
For an example, see HighVideo


1.2.14 NormVideo

Declaration
Procedure NormVideo ;
Description
NormVideo switches the output to the defaults, read at startup. (The defaults are read from the cursor position at startup)

Errors
None.
See also
TextColor, TextBackground, LowVideo, HighVideo
For an example, see HighVideo


1.2.15 NoSound

Declaration
Procedure NoSound ;
Description

Stops the speaker sound. This is not supported in LINUX

Errors
None.
See also
Sound

Example
Program Example16;
uses Crt;

{ Program to demonstrate the Sound and NoSound function. }

var
  i : longint;
begin
  WriteLn('You will hear some tones from your speaker');
  while (i<15000) do
   begin
     inc(i,500);
     Sound(i);
     Delay(100);
   end;
  WriteLn('Quiet now!'); 
  NoSound; {Stop noise}      
end.


1.2.16 ReadKey

Declaration
Function ReadKey : Char;
Description

The ReadKey function reads 1 key from the keyboard buffer, and returns this. If an extended or function key has been pressed, then the zero ASCII code is returned. You can then read the scan code of the key with a second ReadKey call. Remark. Key mappings under Linux can cause the wrong key to be reported by ReadKey, so caution is needed when using ReadKey.

Errors
None.
See also
KeyPressed

Example
Program Example3;
uses Crt;

{ Program to demonstrate the ReadKey function. }

var
  ch : char;
begin
  writeln('Press Left/Right, Esc=Quit');
  repeat
    ch:=ReadKey;
    case ch of
     #0 : begin
            ch:=ReadKey; {Read ScanCode}
            case ch of
             #75 : WriteLn('Left');
             #77 : WriteLn('Right');
	    end;
	  end;
    #27 : WriteLn('ESC');	  
    end;
  until ch=#27 {Esc}           
end.


1.2.17 Sound

Declaration
Procedure Sound (hz : word);
Description
Sounds the speaker at a frequency of hz. This is not supported in LINUX
Errors
None.
See also
NoSound


1.2.18 TextBackground

Declaration
Procedure TextBackground (CL: Byte);
Description

TextBackground sets the background color to CL. CL can be one of the predefined color constants.

Errors
None.
See also
TextColor, HighVideo, LowVideo, NormVideo

Example
Program Example13;
uses Crt;

{ Program to demonstrate the TextBackground function. }

begin
  TextColor(White);
  WriteLn('This is written in with the default background color');
  TextBackground(Green);
  WriteLn('This is written in with a Green background');
  TextBackground(Brown);
  WriteLn('This is written in with a Brown background');
  TextBackground(Black);
  WriteLn('Back with a black background');
end.


1.2.19 TextColor

Declaration
Procedure TextColor (CL: Byte);
Description

TextColor sets the foreground color to CL. CL can be one of the predefined color constants.

Errors
None.
See also
TextBackground, HighVideo, LowVideo, NormVideo

Example
Program Example12;
uses Crt;

{ Program to demonstrate the TextColor function. }

begin
  WriteLn('This is written in the default color');
  TextColor(Red);
  WriteLn('This is written in Red');
  TextColor(White);
  WriteLn('This is written in White');
  TextColor(LightBlue);
  WriteLn('This is written in Light Blue');
end.


1.2.20 TextMode

Declaration
procedure TextMode(Mode: Integer);
Description
TextMode sets the textmode of the screen (i.e. the number of lines and columns of the screen). The lower byte is use to set the VGA text mode.

This procedure is only implemented on DOS.

Errors
None.
See also
Window


1.2.21 WhereX

Declaration
Function WhereX : Byte;
Description

WhereX returns the current X-coordinate of the cursor, relative to the current window. The origin is (1,1), in the upper-left corner of the window.

Errors
None.
See also
GotoXY, WhereY, Window

Example
Program Example7;
uses Crt;

{ Program to demonstrate the WhereX and WhereY functions. }

begin
  Writeln('Cursor postion: X=',WhereX,' Y=',WhereY);
end.


1.2.22 WhereY

Declaration
Function WhereY : Byte;
Description

WhereY returns the current Y-coordinate of the cursor, relative to the current window. The origin is (1,1), in the upper-left corner of the window.

Errors
None.
See also
GotoXY, WhereX, Window

Example
Program Example7;
uses Crt;

{ Program to demonstrate the WhereX and WhereY functions. }

begin
  Writeln('Cursor postion: X=',WhereX,' Y=',WhereY);
end.


1.2.23 Window

Declaration
Procedure Window (X1, Y1, X2, Y2: Byte);
Description
Window creates a window on the screen, to which output will be sent. (X1,Y1) are the coordinates of the upper left corner of the window, (X2,Y2) are the coordinates of the bottom right corner of the window. These coordinates are relative to the entire screen, with the top left corner equal to (1,1) Further coordinate operations, except for the next Window call, are relative to the window's top left corner.

Errors
None.
See also
GotoXY, WhereX, WhereY, ClrScr

Example
Program Example5;
uses Crt;

{ Program to demonstrate the Window function. }

begin
  ClrScr;
  WriteLn('Creating a window from 30,10 to 50,20');
  Window(30,10,50,20);
  WriteLn('We are now writing in this small window we just created, we '+
          'can''t get outside it when writing long lines like this one');
  Write('Press any key to clear the window');
  ReadKey;
  ClrScr;
  Write('The window is cleared, press any key to restore to fullscreen');
  ReadKey;
{Full Screen is 80x25}  
  Window(1,1,80,25);
  Clrscr;
  Writeln('Back in Full Screen');
end.



root
2000-12-20