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Creating two horizontal lines on your screen? (TDesktopCanvas) (Views: 85)


Problem/Question/Abstract:

How do I create lines (or whatever) on the screen?

Answer:

This program demonstrates a TDesktopCanvas. I wrote this to prepare my self for using Trinitron monitors :)  The code parts are gathered from different parts of the www.

program TrinitronTraining;

uses
  Messages, Windows, Graphics, Forms;

type
  TDesktopCanvas = class(TCanvas)
  private
    DC: hDC;
    function GetWidth: Integer;
    function GetHeight: Integer;
  public
    constructor Create;
    destructor Destroy; override;
  published
    property Width: Integer read GetWidth;
    property Height: Integer read GetHeight;
  end;

  { TDesktopCanvas object }

function TDesktopCanvas.GetWidth: Integer;
begin
  Result := GetDeviceCaps(Handle, HORZRES);
end;

function TDesktopCanvas.GetHeight: Integer;
begin
  Result := GetDeviceCaps(Handle, VERTRES);
end;

constructor TDesktopCanvas.Create;
begin
  inherited Create;
  DC := GetDC(0);
  Handle := DC;
end;

destructor TDesktopCanvas.Destroy;
begin
  Handle := 0;
  ReleaseDC(0, DC);
  inherited Destroy;
end;

const
  YCount = 2;

var
  desktop: TDesktopCanvas;
  dx, dy: Integer;
  i: Integer;
  F: array[1..YCount] of TForm;

function CreateLine(Y: Integer): TForm;
begin
  Result := TForm.Create(Application);
  with Result do
  begin
    Left := 0;
    Top := y;
    Width := dx;
    Height := 1;
    BorderStyle := bsNone;
    FormStyle := fsStayOnTop;
    Visible := True;
  end;
end;

procedure ProcessMessage;
var
  Msg: TMsg;
begin
  if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then
    if Msg.Message = WM_QUIT then
      Application.Terminate;
end;

begin
  desktop := TDesktopCanvas.Create;
  try
    dx := desktop.Width;
    dy := desktop.Height div (YCount + 1);
  finally
    desktop.free;
  end;
  for i := 1 to YCount do
    F[i] := CreateLine(i * dy);
  Application.NormalizeTopMosts;
  ShowWindow(Application.Handle, SW_Hide);

  for i := 1 to YCount do
    SetWindowPos(F[i].Handle, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOACTIVATE + SWP_NOMOVE +
      SWP_NOSIZE);

  { use this if you don't want to stop
    repeat
      ProcessMessage;
    until false;
  {}
  Sleep(15000);

  for i := 1 to YCount do
    F[i].Free;
end.

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