delphi - 在Firemonkey上，如何在 Canvas 上绘制蒙版位图？

Question

我有一个位图和一个蒙版(还有一个位图)。我想在蒙版上绘制位图(如下图所示)

如何在 Delphi 上使用 Firemonkey 执行此操作？

Answer 1

使用TBitmap.CreateFromBitmapAndMask()

constructor CreateFromBitmapAndMask(const Bitmap, Mask: TBitmap);

文档说:

The created TBitmap has the value of the Alpha channel of each color pixel equal with the value of the Red channel in the Mask.

进一步:

Tip: For a better result, use a grayscale image for Mask. It has an equal amount of green, red, and blue.

Tip: The mask and the base bitmap must have the same dimensions. Otherwise the new TBitmap will have the dimensions equal to 0.

在一个简单的测试中，例如:

procedure TForm19.Button1Click(Sender: TObject);
var
  bmp, msk: TBitmap;
begin
  bmp := nil;
  msk := nil;
  try
    bmp := TBitmap.Create;
    msk := TBitmap.Create;
    bmp.LoadFromFile('C:\tmp\Imgs\4.bmp');
    msk.LoadFromFile('C:\tmp\Imgs\TestImage04.bmp');
    Image1.Bitmap := bmp;
    Image2.Bitmap := msk;
    Image3.Bitmap.CreateFromBitmapAndMask(bmp, msk);
  finally
    bmp.Free;
    msk.Free;
  end;
end;

结果如下所示:

编辑

为了使 CreateFromBitmapAndMask(bmp, msk); 的结果透明地绘制在表单上，​​在分配给 Image3< 之前必须对其进行预乘/。我们需要以下过程，

procedure PremultiplyBitmapAlpha(bmp:TBitmap);
var
  X, Y: Integer;
  M: TBitmapData;
  C: PAlphaColorRec;
begin
  if bmp.Map(TMapAccess.ReadWrite, M) then
  try
    for Y := 0 to bmp.Height - 1 do
      for X := 0 to bmp.Width - 1 do
      begin
        C := @PAlphaColorArray(M.Data)[Y * (M.Pitch div 4) + X];
        C^.Color := PremultiplyAlpha(C^.Color);
      end;
  finally
    bmp.Unmap(M);
  end;
end;

和另一个用于此目的的临时位图res。测试代码现在如下所示:

procedure TForm14.Button1Click(Sender: TObject);
var
  bmp, msk, res: TBitmap;
begin
  bmp := nil;
  msk := nil;
  res := nil;
  try
    bmp := TBitmap.Create;
    msk := TBitmap.Create;
    bmp.LoadFromFile('C:\tmp\Imgs\4.bmp');
    msk.LoadFromFile('C:\tmp\Imgs\TestImage04.bmp');

    Image1.Bitmap := bmp;
    Image2.Bitmap := msk;

    res := TBitmap.Create;
    res.CreateFromBitmapAndMask(bmp, msk);

    PremultiplyBitmapAlpha(res);
    Image3.Bitmap := res;
  finally
    bmp.Free;
    msk.Free;
    res.Free;
  end;
end;

图像(为了更好的演示而修改了背景颜色):