使用PNG实现半透明的窗体（使用GDI+）

  Delphi中标准控件是不支持png图片的，据说从Window2000后增加gdiplus.dll库处理更多的gdi图像，其中包括png。

  关键的几个api

  GdipCreateBitmapFromFile()，从文件载入图像（不单只Bitmap）

  GdipCreateBitmapFromStreamICM()，从流中入图像

  GdipCreateHBITMAPFromBitmap()，获取图像的位图

  GdipDisposeImage()，释放图像资源

 

  开始直接调用GdipCreateBitmapFromFile没有成功，返回18的错误

  查一下资料这个错误是：“GdiplusNotInitialized”
  看来必须的初始化gdiplus。

  网上找到一套“TGPBitmap”相关的组件，封装了gdiplus的调用。可以参考其中的代码。

 

  png载入后，再取出其位图。特别注意，这个位图是32位的。包括了R、G、B、Alpha四个色值，其中Alpha就是透明度。UpdateLayeredWindow()API函数可以支持Alpha风格。

 

  如何从流中载入？如何将VCL的流处理成IStream？看看代码吧。

 

效果图：

 

准备一张Png图片，编写rc文件，然后加入到工程中。

代码：

CJ7.rc

Png_Cj7 PNG "CJ7.png"

 

CJ7Unit.pas

unit CJ7Unit;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TFormCJ7 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  FormCJ7: TFormCJ7;

implementation

{$R *.dfm}

uses ActiveX;

type
  DebugEventLevel = (
    DebugEventLevelFatal,
    DebugEventLevelWarning
  );
  TDebugEventLevel = DebugEventLevel;

DebugEventProc = procedure(level: DebugEventLevel; message: PChar); stdcall;

GdiplusStartupInput = packed record
    GdiplusVersion: Cardinal;
    DebugEventCallback: DebugEventProc;
    SuppressBackgroundThread: BOOL;
    SuppressExternalCodecs: BOOL;
  end;                          
  TGdiplusStartupInput = GdiplusStartupInput;
  PGdiplusStartupInput = ^TGdiplusStartupInput;

NotificationHookProc = function(out token: ULONG): Integer; stdcall;
  NotificationUnhookProc = procedure(token: ULONG); stdcall;

GdiplusStartupOutput = packed record
    NotificationHook  : NotificationHookProc;
    NotificationUnhook: NotificationUnhookProc;
  end;
  TGdiplusStartupOutput = GdiplusStartupOutput;
  PGdiplusStartupOutput = ^TGdiplusStartupOutput;

function GdipCreateHBITMAPFromBitmap(bitmap: THandle; out hbmReturn: HBITMAP;
  background: Longword): Integer; stdcall; external 'gdiplus.dll';

function GdipCreateBitmapFromFile(filename: PWChar; out bitmap: THandle): Integer;
  stdcall; external 'gdiplus.dll';

function GdipCreateBitmapFromStreamICM(stream: ISTREAM;
  out bitmap: THandle): Integer; stdcall; external 'gdiplus.dll';

function GdipDisposeImage(image: THandle): Integer; stdcall;
  stdcall; external 'gdiplus.dll';

function GdiplusStartup(out token: ULONG; input: PGdiplusStartupInput;
  output: PGdiplusStartupOutput): Integer; stdcall; external 'gdiplus.dll';

procedure GdiplusShutdown(token: ULONG); stdcall; external 'gdiplus.dll';

procedure TFormCJ7.FormCreate(Sender: TObject);
var
  vGdip: THandle;
  vBitmap: HBITMAP;
  vOldBitmap: HBITMAP;
  vPoint1, vPoint2: TPoint;
  vSize: TSize;
  vBlendFunction: TBlendFunction;
  vDC: HDC;
  vBitmapInfo: TBitmapInfoHeader;
  vDIBSection: TDIBSection;
  vBuffer: PChar;
  vStream: IStream;
  vGlobal: THandle;
begin
  SetWindowLong(Handle, GWL_EXSTYLE,
    GetWindowLong(Handle, GWL_EXSTYLE) or WS_EX_LAYERED);
   
  ///////Begin 从资源中载入 
  with TResourceStream.Create(HInstance, 'Png_Cj7', 'PNG') do try
    vGlobal := GlobalAlloc(GHND, Size);
    if vGlobal = 0 then Exit;
    vBuffer := GlobalLock(vGlobal);
    if not Assigned(vBuffer) then Exit;
    try
      Read(vBuffer^, Size);
    finally
      GlobalUnlock(vGdip);
    end;
    if CreateStreamOnHGlobal(vGlobal, False, vStream) <> S_OK then Exit;
    if GdipCreateBitmapFromStreamICM(vStream, vGdip) <> S_OK then Exit;
    GlobalFree(vGlobal);
  finally
    Free;
  end;
  ///////End 从资源中载入

if GdipCreateHBITMAPFromBitmap(vGdip, vBitmap, 0) <> S_OK then Exit;
 
  vBitmapInfo.biSize := SizeOf(vBitmapInfo);
  GetObject(vBitmap, SizeOf(vDIBSection), @vDIBSection);
  vPoint1 := Point(Left, Top);
  vPoint2 := Point(0, 0);
  vSize.cx := vDIBSection.dsBm.bmWidth;
  vSize.cy := vDIBSection.dsBm.bmHeight;
  vBlendFunction.BlendOp := AC_SRC_OVER;
  vBlendFunction.BlendFlags := 0;
  vBlendFunction.SourceConstantAlpha := $FF; // 透明度
  vBlendFunction.AlphaFormat := AC_SRC_ALPHA; //同上
  vDC := CreateCompatibleDC(Canvas.Handle);
  vOldBitmap := SelectObject(vDC, vBitmap);
  UpdateLayeredWindow(Handle, Canvas.Handle,
    @vPoint1, @vSize, vDC, @vPoint2, 0, @vBlendFunction, ULW_ALPHA);
  SelectObject(vDC, vOldBitmap);
  DeleteDC(vDC);
  DeleteObject(vBitmap);
  GdipDisposeImage(vGdip);
end;

procedure TFormCJ7.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  ReleaseCapture;
  Perform(WM_SYSCOMMAND, SC_MOVE or HTCLIENT, 0); // 拖动
end;

var
  vStartupInput: TGDIPlusStartupInput;
  vToken: ULONG;

initialization
  vStartupInput.DebugEventCallback := nil;
  vStartupInput.SuppressBackgroundThread := False;
  vStartupInput.SuppressExternalCodecs   := False;
  vStartupInput.GdiplusVersion := 1;
  GdiplusStartup(vToken, @vStartupInput, nil);

finalization
  GdiplusShutdown(vToken);

end.

想了解gdi+的资料可以参考：

http://msdn2.microsoft.com/en-us/library/ms533798.aspx

http://blog.csdn.net/zswang/article/details/2119649