image - 如何在Delphi中使TImage透明？

Question

在表单上我有两个 TImage。顶部的 TImage 应该是透明的，这样我们就可以看到下面的内容。如何更改TImage透明度级别？

示例:

Answer 1

通常的方法是将所有图形绘制到一个目标 Canvas (可以是 TImage 的位图)，但即使有许多重叠的 TImage，这也可以完成。请注意，您不能重叠 TWinControl。
由于 32 位位图支持透明度，因此可以通过将包含的图形转换为位图(如果需要)来实现这一点。
通过设置 Alphaformat := afDefined 位图将使用来自 alpha channel 的透明度信息进行绘制。
我们需要位图的副本，因为设置 AlphaFormat 会让我们丢失像素信息。
使用扫描线，副本中的像素信息可以传输到目的地，Alpha channel 设置为所需的值。

“一劳永逸”的实现可能如下所示:

type
  pRGBQuadArray = ^TRGBQuadArray;
  TRGBQuadArray = ARRAY [0 .. 0] OF TRGBQuad;

procedure SetImageAlpha(Image:TImage; Alpha: Byte);
var
  pscanLine32,pscanLine32_src: pRGBQuadArray;
  nScanLineCount, nPixelCount : Integer;
  BMP1,BMP2:TBitMap;
  WasBitMap:Boolean;
begin
  if assigned(Image.Picture) then
    begin
       // check if another graphictype than an bitmap is assigned
       // don't check Assigned(Image.Picture.Bitmap) which will return always true
       // since a bitmap is created if needed and the graphic will be discared   
       WasBitMap := Not Assigned(Image.Picture.Graphic);
       if not WasBitMap then
          begin   // let's create a new bitmap from the graphic
            BMP1 := TBitMap.Create;
            BMP1.Assign(Image.Picture.Graphic);
          end
       else BMP1 := Image.Picture.Bitmap;  // take the bitmap

       BMP1.PixelFormat := pf32Bit;

       // we need a copy since setting Alphaformat:= afDefined will clear the Bitmap
       BMP2 := TBitMap.Create;
       BMP2.Assign(BMP1);

       BMP1.Alphaformat := afDefined;

    end;
    for nScanLineCount := 0 to BMP1.Height - 1 do
    begin
      pscanLine32 := BMP1.Scanline[nScanLineCount];
      pscanLine32_src := BMP2.ScanLine[nScanLineCount];
      for nPixelCount := 0 to BMP1.Width - 1 do
        begin
          pscanLine32[nPixelCount].rgbReserved := Alpha;
          pscanLine32[nPixelCount].rgbBlue := pscanLine32_src[nPixelCount].rgbBlue;
          pscanLine32[nPixelCount].rgbRed  := pscanLine32_src[nPixelCount].rgbRed;
          pscanLine32[nPixelCount].rgbGreen:= pscanLine32_src[nPixelCount].rgbGreen;
        end;
    end;
    If not WasBitMap then
      begin  // assign and free Bitmap if we had to create it
      Image.Picture.Assign(BMP1);
      BMP1.Free;
      end;
    BMP2.Free; // free the copy
end;



procedure TForm3.Button1Click(Sender: TObject);
begin  // call for the example image
  SetImageAlpha(Image1,200);
  SetImageAlpha(Image2,128);
  SetImageAlpha(Image3,80);

end;