如何从32 bpp w / o的TBitmap实例创建一个临时DIB部分的alpha混合图标/游标（间接）？ [英] How can I create alpha blended icon/cursor (indirect) from the TBitmap instance of 32 bpp w/o making an temporary DIB section?

问题描述

根据 MS KB条目，在 CreateIconIndirect中有一个怪癖使用 BITMAPV5HEADER 创建可识别 HBITMAP 传递到 CreateDIBSection （和BGRA频道布局）。

According to MS KB entry, there is a quirk in CreateIconIndirect which recognizes HBITMAPs been created with BITMAPV5HEADER passed to CreateDIBSection (and BGRA channel layout).

但是， TBitmap 具有（PixelFormat = pf32bit）和（AlphaFormat = afDefined） （由于其他目的而表现为alpha混合）当它的句柄被引用时不被识别为用于创建图标的有效Alpha混合位图光标。

However, TBitmap instances with (PixelFormat = pf32bit) and (AlphaFormat = afDefined) (behaving as alpha blended for the other purposes) when referred by its Handles are not being recognized as valid alpha blended bitmaps for creation of icons or cursors.

目前，我必须使用描述的API调用创建一个完整的TBitmap副本（见）使 CreateIconIndirect 接受一个位图句柄为alpha混合。如何克服这种笨拙？

Currently, I have to create a full copy of TBitmap using described API calls (see) to make CreateIconIndirect accept a bitmap handle as alpha blended. How do I overcome this clumsiness?

推荐答案

这里有一个例子：

procedure TForm1.Button1Click(Sender: TObject);
const
  crAlpha = TCursor(-25);
var
  Bmp: TBitmap;
  Px: PRGBQuad;
  X, Y: Integer;

  BmpMask: TBitmap;
  II: TIconInfo;
  AlphaCursor: HCURSOR;
begin
  Bmp := TBitmap.Create;
  Bmp.PixelFormat := pf32bit;
  Bmp.Canvas.Brush.Color := clWhite;
  Bmp.SetSize(32, 32);
  Bmp.Canvas.Font.Style := [fsBold];
  Bmp.Canvas.Font.Color := clRed;
  Bmp.Canvas.TextOut(1, 10, 'alpha');

  for Y := 0 to (Bmp.Height - 1) do
  begin
    Px := Bmp.ScanLine[Y];
    for X := 0 to (Bmp.Width - 1) do begin
      if DWORD(Px^) = DWORD(clWhite) then
        Px.rgbReserved := $00
      else
        Px.rgbReserved := $FF;
      Inc(Px);
    end;
  end;

  BmpMask := TBitmap.Create;
  BmpMask.SetSize(Bmp.Width, Bmp.Height);

  II.fIcon := False;
  II.xHotspot := 32;
  II.yHotspot := 32;
  II.hbmMask := BmpMask.Handle;
  II.hbmColor := Bmp.Handle;

  AlphaCursor := CreateIconIndirect(II);
  Win32Check(AlphaCursor <> 0);
  BmpMask.Free;
  Bmp.AlphaFormat := afDefined;  // AlphaBlend below, premultiply channels
  Canvas.Draw(0, 0, Bmp);        // test draw
  Bmp.Free;

  Screen.Cursors[crAlpha] := AlphaCursor;
  Cursor := crAlpha;

end;

（顶部的alpha是测试绘制，另一个是光标）

(Top 'alpha' is test draw, the other is a cursor)

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