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Wiki copytemporary

video unit

The video unit in conjunction with the keyboard unit provide a system-independent way to program interactions with the console, a text terminal. It is part of the FPC’s standard run-time library.

functionality

The provided routines are rather low-level. There is no facility to just print a string at a certain position. Instead, the video unit maintains a buffer of the entire screen. It records every cell’s contents and possibly attributes like colors. The buffer then needs to be written with the updateScreen procedure.

example

Using the following enhancement unit:

pascal
unit videoEnhanced;
{$modeSwitch typeHelpers+}
interface
uses
    video;
type
    {$push}
    {$scopedEnums on}
    color = (black := video.black, blue := video.blue, green := video.green,
        cyan := video.cyan, red := video.red, magenta := video.magenta,
        brown := video.brown, lightGray := video.lightGray,
        darkGray := video.darkGray, lightBlue := video.lightBlue,
        lightGreen := video.lightGreen, lightCyan := video.lightCyan,
        lightRed := video.lightRed, lightMagenta := video.lightMagenta,
        yellow := video.yellow, white := video.white);
    {$pop}
    attribute = bitpacked record
            foreground: color;
            background: color.black..color.lightGray;
            blinking: Boolean;
        end;
    cell = packed record
            {$ifDef endian_big}
                display: attribute;
                character: char;
            {$else}
                character: char;
                display: attribute;
            {$endIf}
        end;
    {$if sizeOf(cell) <> sizeOf(tVideoCell)}
        {$fatal wrong cell size}
    {$endIf}
    dimension = 0..16382{$ifNDef CPU16}+16377{$endIf};
    
    bufferHelper = type helper for pVideoBuf
            function getCell(const x, y: dimension): cell;
            procedure setCell(const x, y: dimension; const content: cell);
            property cell[x, y: dimension]: cell
                read getCell write setCell;
        end;

implementation

function bufferHelper.getCell(const x, y: dimension): cell;
type
    cast = cell; // otherwise `cell` means the _property_
begin
    getCell := cast(self^[x + y * screenWidth]);
end;

procedure bufferHelper.setCell(const x, y: dimension; const content: cell);
begin
    self^[x + y * screenWidth] := tVideoCell(content);
end;
end.

The following program displays a yellow D in the fifth column of the fifth row:

pascal
program videoDemo(input, output, stdErr);
uses
    video, videoEnhanced;
var
    c: cell;
begin
    initVideo;
    if errorCode <> errOK then
    begin
        halt(errorCode);
    end;
    
    c := default(cell);
    c.character := 'D';
    c.display.foreground := color.yellow;
    videoBuf.cell[4, 4] := c;
    
    updateScreen(false);
    
    readLn;
    doneVideo;
    ClearScreen; // Clean up console upon exit
end.

This demo fails to make range checks. This demo assumes colors are available.

see also

From the Free Pascal wiki, page "video unit", as it stood on 2021-10-20 after a change by Ojz0r, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.

Revision 1, last changed by WikiArchive .

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