pascal draw on screen

uDrawScreen.pas

unit uDrawScreen;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls,LCLIntf, LCLType;

type

 { TdrawScreenColor }

 TdrawScreenColor = class(TForm)
    btnRed: TButton;
    btnGreen: TButton;
 procedure btnGreenClick(Sender: TObject);
 procedure btnRedClick(Sender: TObject);
 procedure drawScreen(c:TColor);
 private

 public

 end;

var
  drawScreenColor: TdrawScreenColor;

implementation

{$R *.lfm}

{ TdrawScreenColor }



procedure TdrawScreenColor.btnRedClick(Sender: TObject);
begin
  drawScreen(clRed);
end;

procedure TdrawScreenColor.btnGreenClick(Sender: TObject);
begin
  drawScreen(clGreen);
end;

procedure TdrawScreenColor.drawScreen(c: TColor);
var
  screenCanvas: TCanvas;
begin
  screenCanvas := TCanvas.Create;
  screenCanvas.Brush.Color:=c;
 try
    screenCanvas.Handle := GetDC( 0 );
    screenCanvas.Rectangle(0,0,Screen.DesktopWidth,Screen.DesktopHeight);
 finally
    ReleaseDC( 0, screenCanvas.Handle );
    screenCanvas.Free;
 end;
end;

end.