在Delphi 2010中绘制不透明度椭圆

procedure TForm1.Button1Click(Sender: TObject);
var
  bm1,bm2: TBitmap;
begin
  bm1 := TBitmap.Create;
  bm1.LoadFromFile('C:UsersAndreas RejbrandPicturesportrait.bmp');

  bm2 := TBitmap.Create;
  bm2.SetSize(bm1.Width,bm1.Height);
  bm2.Canvas.Brush.Color := clRed;
  bm2.Canvas.Pen.Style := psClear;
  bm2.Canvas.Ellipse(0,bm2.Width,bm2.Height);

  Canvas.Draw(100,100,bm1);
  Canvas.Draw(100,bm2,127);
end;

Sample 1 http://privat.rejbrand.se/blendimg1.png

如果您想要更多控制,您可以随时手动进行处理：

procedure TForm1.Button1Click(Sender: TObject);
type
  TRGB32Array = packed array[0..MaxInt div SizeOf(TRGBQuad)-1] of TRGBQuad;
  PRGB32Array = ^TRGB32Array;
  TScanline = TRGB32Array;
  PScanline = ^TScanline;
var
  bm1,bm3: TBitmap;
  sc1,sc2,sc3: PScanline;
  i: Integer;
  j: Integer;
var
  transp: real;
const
  opacity = 0.29;
begin
  transp := 1 - opacity;

  bm1 := TBitmap.Create;
  bm1.LoadFromFile('C:UsersAndreas RejbrandPicturesportrait.bmp');

  bm2 := TBitmap.Create;
  bm2.SetSize(bm1.Width,bm2.Height);

  bm3 := TBitmap.Create;
  bm3.SetSize(bm1.Width,bm1.Height);

  bm1.PixelFormat := pf32bit;
  bm2.PixelFormat := pf32bit;
  bm3.PixelFormat := pf32bit;

  for i := 0 to bm1.Height - 1 do
  begin
    sc1 := bm1.ScanLine[i];
    sc2 := bm2.ScanLine[i];
    sc3 := bm3.ScanLine[i];
    for j := 0 to bm1.Width - 1 do
      with sc3^[j] do
      begin
        rgbBlue := round(transp*sc1^[j].rgbBlue + opacity*sc2^[j].rgbBlue);
        rgbGreen := round(transp*sc1^[j].rgbGreen + opacity*sc2^[j].rgbGreen);
        rgbRed := round(transp*sc1^[j].rgbRed + opacity*sc2^[j].rgbRed);
      end;
  end;

  Canvas.Draw(100,bm3);

end;

Sample 2 http://privat.rejbrand.se/blendimg2.png

例如,您可以让背景图像在椭圆外的100％不透明度：

...
  for i := 0 to bm1.Height - 1 do
  begin
    sc1 := bm1.ScanLine[i];
    sc2 := bm2.ScanLine[i];
    sc3 := bm3.ScanLine[i];
    for j := 0 to bm1.Width - 1 do
      if sc2^[j].rgbBlue + sc2^[j].rgbGreen + sc2^[j].rgbRed = 3*255 then
        sc3^[j] := sc1^[j]
      else
        with sc3^[j] do
        begin
          rgbBlue := round(transp*sc1^[j].rgbBlue + opacity*sc2^[j].rgbBlue);
          rgbGreen := round(transp*sc1^[j].rgbGreen + opacity*sc2^[j].rgbGreen);
          rgbRed := round(transp*sc1^[j].rgbRed + opacity*sc2^[j].rgbRed);
        end;
  end;
  ...

Sample 3 http://privat.rejbrand.se/blendimg3.png

更不用说all other cool stuff you can do with pixmap manipulation：

...
  for i := 0 to bm1.Height - 1 do
  begin
    sc1 := bm1.ScanLine[i];
    sc2 := bm2.ScanLine[i];
    sc3 := bm3.ScanLine[i];
    for j := 0 to bm1.Width - 1 do
      if sc2^[j].rgbBlue + sc2^[j].rgbGreen + sc2^[j].rgbRed = 3*255 then
        sc3^[j] := sc1^[j]
      else
        with sc3^[j] do
        begin
          rgbBlue := round(sin(transp*sc1^[j].rgbBlue + opacity*sc2^[j].rgbBlue));
          rgbGreen := round(transp*sc1^[j].rgbGreen + opacity*sc2^[j].rgbGreen);
          rgbRed := round(transp*sc1^[j].rgbRed + opacity*sc2^[j].rgbRed);
        end;
  end;
  ...

Sample 4 http://privat.rejbrand.se/blendimg4.png

如果你真的不想手动操作,我只是想通了,你可以在第一个位图的副本上绘制椭圆,然后混合这两个位图：

procedure TForm1.Button1Click(Sender: TObject);
var
  bm1,bm2: TBitmap;
begin

  bm1 := TBitmap.Create;
  bm1.LoadFromFile('C:UsersAndreas RejbrandPicturesportrait.bmp');

  bm2 := TBitmap.Create;
  bm2.LoadFromFile('C:UsersAndreas RejbrandPicturesportrait.bmp');
  bm2.Canvas.Brush.Color := clRed;
  bm2.Canvas.Pen.Style := psClear;
  bm2.Canvas.Ellipse(0,127);
end;

Sample 5 http://privat.rejbrand.se/blendimg5.png