Рисовать в Win32 как в Paint

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, jpeg, ExtCtrls, StdCtrls, Buttons;
 
type
  TForm1 = class(TForm)
    Image1: TImage;
    Image2: TImage;
    BitBtn1: TBitBtn;
    procedure BitBtn1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
const
 AC_SRC_ALPHA = $50;
 
procedure DrawAlphaBlend (hWnd : HWND;  hdcwnd : HDC);
var
    Ahdc : HDC;              // handle of the DC we will create
    bf : BLENDFUNCTION;      // structure for alpha blending
    Ahbitmap : HBITMAP;      // bitmap handle
    bmi : BITMAPINFO;        // bitmap header
    pvBits : pointer;        // pointer to DIB section
    ulWindowWidth,
    ulWindowHeight : ULONG;  // window width/height
    ulBitmapWidth,
    ulBitmapHeight : ULONG; // bitmap width/height
    rt : TRect;             // used for getting window dimensions
begin
    // get window dimensions
    GetClientRect(hWnd, rt);
 
    // calculate window width/height
    ulWindowWidth := rt.right - rt.left;
    ulWindowHeight := rt.bottom - rt.top;
 
    // make sure we have at least some window size
    if ((ulWindowWidth = 0 ) and  (ulWindowHeight=0)) then
        exit;
 
    // divide the window into 3 horizontal areas
    ulWindowHeight := trunc(ulWindowHeight / 3);
 
    // create a DC for our bitmap -- the source DC for AlphaBlend
    Ahdc := CreateCompatibleDC(hdcwnd);
 
    // zero the memory for the bitmap info
    ZeroMemory(@bmi, sizeof(BITMAPINFO));
 
    // setup bitmap info
    bmi.bmiHeader.biSize := sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth := trunc(ulWindowWidth - (ulWindowWidth/5)*2);
    ulBitmapWidth := trunc(ulWindowWidth - (ulWindowWidth/5)*2);
    bmi.bmiHeader.biHeight := trunc(ulWindowHeight - (ulWindowHeight/5)*2);
    ulBitmapHeight := trunc(ulWindowHeight - (ulWindowHeight/5)*2);
    bmi.bmiHeader.biPlanes := 1;
    bmi.bmiHeader.biBitCount := 32;         // four 8-bit components
    bmi.bmiHeader.biCompression := BI_RGB;
    bmi.bmiHeader.biSizeImage := ulBitmapWidth * ulBitmapHeight * 4;
 
    // create our DIB section and select the bitmap into the dc
    Ahbitmap := CreateDIBSection(Ahdc, bmi, DIB_RGB_COLORS, pvBits, 0, 0);
    SelectObject(Ahdc, Ahbitmap);
 
    bf.BlendOp := AC_SRC_OVER;
    bf.BlendFlags := 0;
    bf.SourceConstantAlpha := $7f;  // half of 0xff = 50% transparency
    bf.AlphaFormat := 0;             // ignore source alpha channel
 
    AlphaBlend(hdcwnd, trunc(ulWindowWidth/5), trunc(ulWindowHeight/5),
                    ulBitmapWidth, ulBitmapHeight,
                    Ahdc, 0, 0, ulBitmapWidth, ulBitmapHeight, bf);
 
 
    bf.BlendOp := AC_SRC_OVER;
    bf.BlendFlags := 0;
    bf.AlphaFormat := AC_SRC_ALPHA;  // use source alpha
    bf.SourceConstantAlpha := $ff;  // opaque (disable constant alpha)
 
    AlphaBlend(hdcwnd, trunc(ulWindowWidth/5),
     trunc(ulWindowHeight/5+ulWindowHeight), ulBitmapWidth, ulBitmapHeight,
      Ahdc, 0, 0, ulBitmapWidth, ulBitmapHeight, bf);
 
    bf.BlendOp := AC_SRC_OVER;
    bf.BlendFlags := 0;
    bf.AlphaFormat := 0;
    bf.SourceConstantAlpha := $3A;
 
    AlphaBlend(hdcwnd, trunc(ulWindowWidth/5),
               trunc(ulWindowHeight/5+2*ulWindowHeight), ulBitmapWidth,
               ulBitmapHeight, Ahdc, 0, 0, ulBitmapWidth,
               ulBitmapHeight, bf);
 
    // do cleanup
    DeleteObject(Ahbitmap);
    DeleteDC(Ahdc);
 
end;
procedure TForm1.BitBtn1Click(Sender: TObject);
begin
DrawAlphaBlend ( Handle, Image2.Picture.Bitmap.Handle);
end;
 
end.