windows – 为什么自定义光标图像显示不正确？

背景

我编写了一个函数,它根据与给定设备上下文关联的位图创建自定义光标.我使用它来创建拖拽光标,显示为“撕下” – 有点像它们在“Trello”中使用.

我一直在使用该函数一段时间没有问题,但当我使用它与新的树组件我正在努力它开始创建部分空白游标.

我已经验证了Delphi 2010和Delphi Berlin都出现了这个问题,并且我也验证了它在Windows 7和Windows 10中都被破坏了.

这是一张显示光标应该是什么样子的照片(对不起 – 找不到快速浏览光标的方法)：

而且当它部分空白时它看起来像是什么(好吧,它不仅仅是部分空白 – 它实际上是不可见的)：

故障排除

在我发现故障排除之后,如果在调用GetDragCursor之前将PNG图像写入与DC关联的位图,则光标会混乱.

这是我能想到的最简单的代码,用于演示问题：

包含两个TPaintBox组件的表单：MyPaintBoxWorks和MyPaintBoxBroken.

>当您单击MyPaintBoxWorks时,您将获得预期的光标.
>当您单击MyPaintBoxBroken时,您只需获取png图像.

为了使其易于阅读(我希望),我已经排除了所有错误和资源处理.这对问题没有影响.
为了使其工作,您需要访问Png图像.任何png图像都可以.然后更新代码以加载图像.

uses
  Types,pngimage;

//////////////////////////////////////////////////////////////////////
procedure TMyForm.FormPaint(Sender: TObject);
begin
  MyPaintBoxWorks.Canvas.Brush.Color := clGreen;
  MyPaintBoxWorks.Canvas.Rectangle( 0,MyPaintBoxWorks.Width,MyPaintBoxWorks.Height );
  MyPaintBoxBroken.Canvas.Brush.Color := clRed;
  MyPaintBoxBroken.Canvas.Rectangle( 0,MyPaintBoxBroken.Width,MyPaintBoxBroken.Height );
end;

function GetDragCursor( Handle: HDC;
                        Width,Height: integer;
                        CursorX,CursorY: integer ): TCursor; forward;


//////////////////////////////////////////////////////////////////////
procedure TMyForm.MyPaintBoxWorksMouseDown( Sender: TObject;
                                            Button: TMouseButton;
                                            Shift: TShiftState;
                                            X,Y: Integer);
begin
  Screen.Cursor := GetDragCursor( MyPaintBoxWorks.Canvas.Handle,MyPaintBoxWorks.Height,X,Y );
end;


//////////////////////////////////////////////////////////////////////
procedure TMyForm.MyPaintBoxBrokenMouseDown( Sender: TObject;
                                             Button: TMouseButton;
                                             Shift: TShiftState;
                                             X,Y: Integer );
var
  Img: TPngImage;

begin
  Img := TPngImage.Create;
  Img.LoadFromFile( 'D:TestImage.png' );
  Img.Draw( MyPaintBoxBroken.Canvas,Rect( 20,20,40,40 ) );
  Screen.Cursor := GetDragCursor( MyPaintBoxBroken.Canvas.Handle,MyPaintBoxBroken.Height,Y );
end;


//////////////////////////////////////////////////////////////////////
function GetDragCursor( Handle: HDC;
                        Width,CursorY: integer ): TCursor;
var
  MaskDC           : HDC;
  OrgMaskBmp       : HBITMAP;
  MaskBmp          : HBITMAP;
  ColourDC         : HDC;
  OrgColourBmp     : HBITMAP;
  ColourBmp        : HBITMAP;
  IconInfo         : TIconInfo;
  Brush            : HBRUSH;

begin
  // Create Colour bitmap
  // ====================
  ColourDC := CreateCompatibleDC( Handle );
  ColourBmp := CreateCompatibleBitmap( Handle,Width,Height );
  OrgColourBmp := SelectObject( ColourDC,ColourBmp );

  BitBlt( ColourDC,Height,Handle,SRCCOPY );

  SelectObject( ColourDC,OrgColourBmp );

  // Create Mask bitmap
  // ==================
  MaskDC := CreateCompatibleDC( Handle );
  MaskBmp := CreateCompatibleBitmap( Handle,Height );
  OrgMaskBmp := SelectObject( MaskDC,MaskBmp );

  // Fill with white
  Brush := CreateSolidBrush( $FFFFFF );
  FillRect( MaskDC,Rect( 0,Height ),Brush );
  DeleteObject( Brush );

  // Fill masked area with black
  Brush := CreateSolidBrush( $000000 );
  FillRect( MaskDC,Brush );
  DeleteObject( Brush );

  SelectObject( MaskDC,OrgMaskBmp );

  // Create and set cursor
  // =====================
  with iconInfo do
  begin
    fIcon :=    FALSE;
    xHotspot := CursorX;
    yHotspot := CursorY;
    hbmMask :=  MaskBmp;
    hbmColor := ColourBmp;
  end;
  Screen.Cursors[1] := CreateIconIndirect( iconInfo );
  Result := 1;
end;

我已经详细研究了函数和微软文档,我发现函数没有任何问题.

我也研究过TPngImage.Draw,看不出任何明显的错误(我不应该这么想).功能：

>依次调用TPngImage.DrawPartialTrans
>通过CreateDIBSection创建位图
>扫描像素并计算alpha混合RGB值
>使用指针算术来移动像素缓冲区
>调用BitBlt将最终图像复制到DC中

(我在问题的最后包含了函数的代码以供参考)

如果我：总是正确生成游标：

>注释掉写入像素缓冲区的代码,或
>仅扫描图像中的前几行,或
>评论最终对BitBlt的调用

这看起来像缓冲区溢出,但代码中没有任何东西似乎支持这一点.而且,我的代码更有可能是错误的.

题

我的函数GetDragCursor或DrawPartialTrans中有什么错误或看起来可疑吗？

procedure TPngImage.DrawPartialTrans(DC: HDC; Rect: TRect);
  {Adjust the rectangle structure}
  procedure AdjustRect(var Rect: TRect);
  var
    t: Integer;
  begin
    if Rect.Right < Rect.Left then
    begin
      t := Rect.Right;
      Rect.Right := Rect.Left;
      Rect.Left := t;
    end;
    if Rect.Bottom < Rect.Top then
    begin
      t := Rect.Bottom;
      Rect.Bottom := Rect.Top;
      Rect.Top := t;
    end
  end;

type
  {Access to pixels}
  TPixelLine = Array[Word] of TRGBQuad;
  pPixelLine = ^TPixelLine;
const
  {Structure used to create the bitmap}
  BitmapInfoHeader: TBitmapInfoHeader =
    (biSize: sizeof(TBitmapInfoHeader);
     biWidth: 100;
     biHeight: 100;
     biPlanes: 1;
     biBitCount: 32;
     biCompression: BI_RGB;
     biSizeImage: 0;
     biXPelsPerMeter: 0;
     biYPelsPerMeter: 0;
     biClrUsed: 0;
     biClrImportant: 0);
var
  {Buffer bitmap creation}
  BitmapInfo  : TBitmapInfo;
  BufferDC    : HDC;
  BufferBits  : Pointer;
  OldBitmap,BufferBitmap: HBitmap;
  Header: TChunkIHDR;

  {Transparency/palette chunks}
  TransparencyChunk: TChunktRNS;
  PaletteChunk: TChunkPLTE;
  TransValue,PaletteIndex: Byte;
  CurBit: Integer;
  Data: PByte;

  {Buffer bitmap modification}
  BytesPerRowDest,BytesPerRowSrc,BytesPerRowAlpha: Integer;
  ImageSource,ImageSourceOrg,AlphaSource     : pByteArray;
  ImageData       : pPixelLine;
  i,j,i2,j2    : Integer;

  {For bitmap stretching}
  W,H            : Cardinal;
  Stretch         : Boolean;
  FactorX,FactorY: Double;

begin
  {Prepares the rectangle structure to stretch draw}
  if (Rect.Right = Rect.Left) or (Rect.Bottom = Rect.Top) then exit;
  AdjustRect(Rect);
  {Gets the width and height}
  W := Rect.Right - Rect.Left;
  H := Rect.Bottom - Rect.Top;
  Header := Self.Header; {Fast access to header}
  Stretch := (W <> Header.Width) or (H <> Header.Height);
  if Stretch then FactorX := W / Header.Width else FactorX := 1;
  if Stretch then FactorY := H / Header.Height else FactorY := 1;

  {Prepare to create the bitmap}
  Fillchar(BitmapInfo,sizeof(BitmapInfo),#0);
  BitmapInfoHeader.biWidth := W;
  BitmapInfoHeader.biHeight := -Integer(H);
  BitmapInfo.bmiHeader := BitmapInfoHeader;

  {Create the bitmap which will receive the background,the applied}
  {alpha blending and then will be painted on the background}
  BufferDC := CreateCompatibleDC(0);
  {In case BufferDC could not be created}
  if (BufferDC = 0) then RaiseError(EPNGOutMemory,EPNGOutMemoryText);
  BufferBitmap := CreateDIBSection(BufferDC,BitmapInfo,DIB_RGB_COLORS,BufferBits,0);
  {In case buffer bitmap could not be created}
  if (BufferBitmap = 0) or (BufferBits = Nil) then
  begin
    if BufferBitmap <> 0 then DeleteObject(BufferBitmap);
    DeleteDC(BufferDC);
    RaiseError(EPNGOutMemory,EPNGOutMemoryText);
  end;

  {Selects new bitmap and release old bitmap}
  OldBitmap := SelectObject(BufferDC,BufferBitmap);

  {Draws the background on the buffer image}
  BitBlt(BufferDC,W,H,DC,Rect.Left,Rect.Top,SRCCOPY);

  {Obtain number of bytes for each row}
  BytesPerRowAlpha := Header.Width;
  BytesPerRowDest := (((BitmapInfo.bmiHeader.biBitCount * W) + 31)
    and not 31) div 8; {Number of bytes for each image row in destination}
  BytesPerRowSrc := (((Header.BitmapInfo.bmiHeader.biBitCount * Header.Width) +
    31) and not 31) div 8; {Number of bytes for each image row in source}

  {Obtains image pointers}
  ImageData := BufferBits;
  AlphaSource := Header.ImageAlpha;
  Longint(ImageSource) := Longint(Header.ImageData) +
    Header.BytesPerRow * Longint(Header.Height - 1);
  ImageSourceOrg := ImageSource;

  case Header.BitmapInfo.bmiHeader.biBitCount of
    {R,G,B images}
    24:
      FOR j := 1 TO H DO
      begin
        {Process all the pixels in this line}
        FOR i := 0 TO W - 1 DO
        begin
          if Stretch then i2 := trunc(i / FactorX) else i2 := i;
          {Optmize when we dont have transparency}
          if (AlphaSource[i2] <> 0) then
            if (AlphaSource[i2] = 255) then
            begin
              pRGBTriple(@ImageData[i])^ := pRGBTriple(@ImageSource[i2 * 3])^;
              ImageData[i].rgbReserved := 255;
            end
            else
              with ImageData[i] do
              begin
                rgbRed := ($7F + ImageSource[2+i2*3] * AlphaSource[i2] + rgbRed *
                  (not AlphaSource[i2])) div $FF;
                rgbGreen := ($7F + ImageSource[1+i2*3] * AlphaSource[i2] +
                  rgbGreen * (not AlphaSource[i2])) div $FF;
                rgbBlue := ($7F + ImageSource[i2*3] * AlphaSource[i2] + rgbBlue *
                 (not AlphaSource[i2])) div $FF;
                rgbReserved := not (($7F + (not rgbReserved) * (not AlphaSource[i2])) div $FF);
            end;
          end;

        {Move pointers}
        inc(Longint(ImageData),BytesPerRowDest);
        if Stretch then j2 := trunc(j / FactorY) else j2 := j;
        Longint(ImageSource) := Longint(ImageSourceOrg) - BytesPerRowSrc * j2;
        Longint(AlphaSource) := Longint(Header.ImageAlpha) +
          BytesPerRowAlpha * j2;
      end;
    {Palette images with 1 byte for each pixel}
    1,4,8: if Header.ColorType = COLOR_GRAYSCALEALPHA then
      FOR j := 1 TO H DO
      begin
        {Process all the pixels in this line}
        FOR i := 0 TO W - 1 DO
          with ImageData[i],Header.BitmapInfo do begin
            if Stretch then i2 := trunc(i / FactorX) else i2 := i;
            rgbRed := ($7F + ImageSource[i2] * AlphaSource[i2] +
              rgbRed * (not AlphaSource[i2])) div $FF;
            rgbGreen := ($7F + ImageSource[i2] * AlphaSource[i2] +
              rgbGreen * (not AlphaSource[i2])) div $FF;
            rgbBlue := ($7F + ImageSource[i2] * AlphaSource[i2] +
              rgbBlue * (not AlphaSource[i2])) div $FF;
            rgbReserved := not (($7F + (not rgbReserved) * (not AlphaSource[i2])) div $FF);
          end;

        {Move pointers}
        Longint(ImageData) := Longint(ImageData) + BytesPerRowDest;
        if Stretch then j2 := trunc(j / FactorY) else j2 := j;
        Longint(ImageSource) := Longint(ImageSourceOrg) - BytesPerRowSrc * j2;
        Longint(AlphaSource) := Longint(Header.ImageAlpha) +
          BytesPerRowAlpha * j2;
      end
    else {Palette images}
    begin
      {Obtain pointer to the transparency chunk}
      TransparencyChunk := TChunktRNS(Chunks.ItemFromClass(TChunktRNS));
      PaletteChunk := TChunkPLTE(Chunks.ItemFromClass(TChunkPLTE));

      FOR j := 1 TO H DO
      begin
        {Process all the pixels in this line}
        i := 0;
        repeat
          CurBit := 0;
          if Stretch then i2 := trunc(i / FactorX) else i2 := i;
          Data := @ImageSource[i2];

          repeat
            {Obtains the palette index}
            case Header.BitDepth of
              1: PaletteIndex := (Data^ shr (7-(I Mod 8))) and 1;
            2,4: PaletteIndex := (Data^ shr ((1-(I Mod 2))*4)) and $0F;
             else PaletteIndex := Data^;
            end;

            {Updates the image with the new pixel}
            with ImageData[i] do
            begin
              TransValue := TransparencyChunk.PaletteValues[PaletteIndex];
              rgbRed := (255 + PaletteChunk.Item[PaletteIndex].rgbRed *
                 TransValue + rgbRed * (255 - TransValue)) shr 8;
              rgbGreen := (255 + PaletteChunk.Item[PaletteIndex].rgbGreen *
                 TransValue + rgbGreen * (255 - TransValue)) shr 8;
              rgbBlue := (255 + PaletteChunk.Item[PaletteIndex].rgbBlue *
                 TransValue + rgbBlue * (255 - TransValue)) shr 8;
            end;

            {Move to next data}
            inc(i); inc(CurBit,Header.BitmapInfo.bmiHeader.biBitCount);
          until CurBit >= 8;
          {Move to next source data}
          //inc(Data);
        until i >= Integer(W);

        {Move pointers}
        Longint(ImageData) := Longint(ImageData) + BytesPerRowDest;
        if Stretch then j2 := trunc(j / FactorY) else j2 := j;
        Longint(ImageSource) := Longint(ImageSourceOrg) - BytesPerRowSrc * j2;
      end
    end {Palette images}
  end {case Header.BitmapInfo.bmiHeader.biBitCount};

  {Draws the new bitmap on the foreground}
  BitBlt(DC,BufferDC,SRCCOPY);

  {Free bitmap}
  SelectObject(BufferDC,OldBitmap);
  DeleteObject(BufferBitmap);
  DeleteDC(BufferDC);
end;

你的GetDragCursor对我很有用.

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