unit UMain;

interface

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

type
  TfrmMain = class(TForm)
    mnuMain: TMainMenu;
    mnuFile: TMenuItem;
    mnuExit: TMenuItem;
    imgTile: TImage;
    mnuOptions: TMenuItem;
    mnuBitmap: TMenuItem;
    mnuGradient: TMenuItem;
    procedure mnuExitClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure mnuBitmapClick(Sender: TObject);
    procedure mnuGradientClick(Sender: TObject);
    procedure FormCloseQuery(Sender: TObject; var CanClose: Boolean);
    procedure FormResize(Sender: TObject);
    procedure FormPaint(Sender: TObject);
  private
    { Private declarations }
    MDIDefProc: pointer;
    MDIInstance: TFarProc;
    procedure MDIWndProc(var prmMsg: TMessage);
    procedure CreateWnd; override;
    procedure ShowBitmap(prmDC: hDC);
    procedure ShowGradient(prmDC: hDC; prmRed, prmGreen, prmBlue: byte);
  public
    { Public declarations }
  end;

var

  frmMain: TfrmMain;
  glbImgWidth: integer;
  glbImgHeight: integer;

implementation

{$R *.DFM}

procedure TfrmMain.FormCreate(Sender: TObject);
begin

  glbImgHeight := imgTile.Picture.Height;
  glbImgWidth := imgTile.Picture.Width;
end;

procedure TfrmMain.FormResize(Sender: TObject);
begin

  FormPaint(Sender);
end;

procedure TfrmMain.MDIWndProc(var prmMsg: TMessage);
begin

  with prmMsg do
  begin
    if Msg = WM_ERASEBKGND then
    begin
      if mnuBitmap.Checked then
        ShowBitmap(wParam)
      else
        ShowGradient(wParam, 255, 0, 0);
      Result := 1;
    end
    else
      Result := CallWindowProc(MDIDefProc, ClientHandle, Msg, wParam, lParam);
  end;
end;

procedure TfrmMain.CreateWnd;
begin

  inherited CreateWnd;
  MDIInstance := MakeObjectInstance(MDIWndProc); { создаем ObjectInstance }
  MDIDefProc := pointer(SetWindowLong(ClientHandle, GWL_WNDPROC,
    longint(MDIInstance)));
end;

procedure TfrmMain.FormCloseQuery(Sender: TObject; var CanClose:
  Boolean);
begin

  { восстанавоиваем proc окна по умолчанию }
  SetWindowLong(ClientHandle, GWL_WNDPROC, longint(MDIDefProc));
  { избавляемся от ObjectInstance }
  FreeObjectInstance(MDIInstance);
end;

procedure TfrmMain.mnuExitClick(Sender: TObject);
begin

  close;
end;

procedure TfrmMain.mnuBitmapClick(Sender: TObject);

var
  wrkDC: hDC;
begin

  wrkDC := GetDC(ClientHandle);
  ShowBitmap(wrkDC);
  ReleaseDC(ClientHandle, wrkDC);
  mnuBitmap.Checked := true;
  mnuGradient.Checked := false;
end;

procedure TfrmMain.mnuGradientClick(Sender: TObject);
var
  wrkDC: hDC;
begin
  wrkDC := GetDC(ClientHandle);
  ShowGradient(wrkDC, 0, 0, 255);
  ReleaseDC(ClientHandle, wrkDC);
  mnuGradient.Checked := true;
  mnuBitMap.Checked := false;
end;

procedure TfrmMain.ShowBitmap(prmDC: hDC);
var
  wrkSource: TRect;
  wrkTarget: TRect;
  wrkX: integer;
  wrkY: integer;
begin
  { заполняем (tile) окно изображением }
  if FormStyle = fsNormal then
  begin
    wrkY := 0;
    while wrkY < ClientHeight do { заполняем сверху вниз.. }
    begin
      wrkX := 0;
      while wrkX < ClientWidth do { ..и слева направо. }
      begin
        Canvas.Draw(wrkX, wrkY, imgTile.Picture.Bitmap);
        Inc(wrkX, glbImgWidth);
      end;
      Inc(wrkY, glbImgHeight);
    end;
  end
  else if FormStyle = fsMDIForm then
  begin
    Windows.GetClientRect(ClientHandle, wrkTarget);
    wrkY := 0;
    while wrkY < wrkTarget.Bottom do
    begin
      wrkX := 0;
      while wrkX < wrkTarget.Right do
      begin
        BitBlt(longint(prmDC), wrkX, wrkY, imgTile.Width, imgTile.Height,
          imgTile.Canvas.Handle, 0, 0, SRCCOPY);
        Inc(wrkX, glbImgWidth);
      end;
      Inc(wrkY, glbImgHeight);
    end;
  end;
end;

procedure TfrmMain.ShowGradient(prmDC: hDC; prmRed, prmGreen, prmBlue: byte);
var
  wrkBrushNew: hBrush;
  wrkBrushOld: hBrush;
  wrkColor: TColor;
  wrkCount: integer;
  wrkDelta: integer;
  wrkRect: TRect;
  wrkSize: integer;
  wrkY: integer;
begin
  { процедура заполнения градиентной заливкой }
  wrkDelta := 255 div (1 + ClientHeight); { желаемое количество оттенков }
  if wrkDelta = 0 then
    wrkDelta := 1; { да, обычно 1 }
  wrkSize := ClientHeight div 240; { размер смешанных баров }
  if wrkSize = 0 then
    wrkSize := 1;
  for wrkY := 0 to 1 + (ClientHeight div wrkSize) do
  begin
    wrkColor := RGB(prmRed, prmGreen, prmBlue);
    wrkRect := Rect(0, wrkY * wrkSize, ClientWidth, (wrkY + 1) * wrkSize);
    if FormStyle = fsNormal then
    begin
      Canvas.Brush.Color := wrkColor;
      Canvas.FillRect(wrkRect);
    end
    else if FormStyle = fsMDIForm then
    begin
      wrkBrushNew := CreateSolidBrush(wrkColor);
      wrkBrushOld := SelectObject(prmDC, wrkBrushNew);
      FillRect(prmDC, wrkRect, wrkBrushNew);
      SelectObject(prmDC, wrkBrushOld);
      DeleteObject(wrkBrushNew);
    end;
    if prmRed > wrkDelta then
      Dec(prmRed, wrkDelta);
    if prmGreen > wrkDelta then
      Dec(prmGreen, wrkDelta);
    if prmBlue > wrkDelta then
      Dec(prmBlue, wrkDelta);
  end;
end;

procedure TfrmMain.FormPaint(Sender: TObject);
begin
  if FormStyle = fsNormal then
    if mnuBitMap.Checked then
      mnuBitMapClick(Sender)
    else
      mnuGradientClick(Sender);
end;

end.