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How to handle bitmap layers (Views: 100)


Problem/Question/Abstract:

I want to overlay bitmap2 over bitmap. The bitmap2 should be on top of bitmap1, i.e. the end result should be that bitmap2 should also show bits of bitmap1. What is the best way in Delphi to handle this?

Answer:

There are two methods. One works using a TImageList the other without. So the latter will work with other file types besides BMP's. Here's the code for both, it's pretty clear how both work. The key thing is you must specify a transparent color:

procedure DrawTrans(DestCanvas: TCanvas; X, Y: smallint; SrcBitmap: TBitmap; AColor: TColor);
var
  ANDBitmap, ORBitmap: TBitmap;
  CM: TCopyMode;
  Src: TRect;
begin
  ANDBitmap := nil;
  ORBitmap := nil;
  try
    ANDBitmap := TBitmap.Create;
    ORBitmap := TBitmap.Create;
    Src := Bounds(0, 0, SrcBitmap.Width, SrcBitmap.Height);
    with ORBitmap do
    begin
      Width := SrcBitmap.Width;
      Height := SrcBitmap.Height;
      Canvas.Brush.Color := clBlack;
      Canvas.CopyMode := cmSrcCopy;
      Canvas.BrushCopy(Src, SrcBitmap, Src, AColor);
    end;
    with ANDBitmap do
    begin
      Width := SrcBitmap.Width;
      Height := SrcBitmap.Height;
      Canvas.Brush.Color := clWhite;
      Canvas.CopyMode := cmSrcInvert;
      Canvas.BrushCopy(Src, SrcBitmap, Src, AColor);
    end;
    with DestCanvas do
    begin
      CM := CopyMode;
      CopyMode := cmSrcAnd;
      Draw(X, Y, ANDBitmap);
      CopyMode := cmSrcPaint;
      Draw(X, Y, ORBitmap);
      CopyMode := CM;
    end;
  finally
    ANDBitmap.Free;
    ORBitmap.Free;
  end;
end;

The other way:

abitmap := TBitmap.Create;
imagelist1.Clear;
abitmap.LoadFromFile('1.bmp');
imagelist1.AddMasked(abitmap, clNone);
abitmap.Empty;
abitmap.LoadFromFile('e1.bmp');
imagelist1.AddMasked(abitmap, clWhite);
abitmap.Empty;
abitmap.LoadFromFile('h1.bmp');
imagelist1.AddMasked(abitmap, clWhite);
imagelist1.Draw(image1.Canvas, 0, 0, 0);
imagelist1.Draw(image1.Canvas, 0, 0, 1);
imagelist1.Draw(image1.Canvas, 0, 0, 2);
abitmap.free;

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