如何在 pf32bit bitmap 中创建阴影效果？

Question

I found this code that works fine with pf24bit . How change to work with pf32bit (or any other PixelFormat )?

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Edit :

For example if you get a screenshot, this code doesn't apply effect in full bitmap width. To bitmap height it's ok.

Answer 1

This is straightforward.

A 24-bpp image has format BGR and a 32-bpp image has format BGRA, where the alpha component is typically not used for anything. To blacken the bitmap, we simply ignore the A component.

So, 24 bits per pixel:

procedure FadeBitmap24(ABitmap: TBitmap);
type
  PRGBTripleArray = ^TRGBTripleArray;
  TRGBTripleArray = array[Word] of TRGBTriple;
var
  SL: PRGBTripleArray;
  y: Integer;
  x: Integer;
begin

  ABitmap.PixelFormat := pf24bit;

  for y := 0 to ABitmap.Height - 1 do
  begin
    SL := ABitmap.ScanLine[y];
    for x := 0 to ABitmap.Width - 1 do
      with SL[x] do
      begin
        rgbtRed := rgbtRed div 2;
        rgbtGreen := rgbtGreen div 2;
        rgbtBlue := rgbtBlue div 2;
      end;
  end;

end;

32 bits per pixel:

procedure FadeBitmap32(ABitmap: TBitmap);
type
  PRGBQuadArray = ^TRGBQuadArray;
  TRGBQuadArray = array[Word] of TRGBQuad;
var
  SL: PRGBQuadArray;
  y: Integer;
  x: Integer;
begin

  ABitmap.PixelFormat := pf32bit;

  for y := 0 to ABitmap.Height - 1 do
  begin
    SL := ABitmap.ScanLine[y];
    for x := 0 to ABitmap.Width - 1 do
      with SL[x] do
      begin
        rgbRed := rgbRed div 2;
        rgbGreen := rgbGreen div 2;
        rgbBlue := rgbBlue div 2;
      end;
  end;

end;

This is a direct translation.

But both versions can be written more elegantly:

procedure FadeBitmap24(ABitmap: TBitmap);
begin

  ABitmap.PixelFormat := pf24bit;

  for var y := 0 to ABitmap.Height - 1 do
  begin
    var SL := PRGBTriple(ABitmap.ScanLine[y]);
    for var x := 0 to ABitmap.Width - 1 do
    begin
      SL.rgbtRed := SL.rgbtRed div 2;
      SL.rgbtGreen := SL.rgbtGreen div 2;
      SL.rgbtBlue := SL.rgbtBlue div 2;
      Inc(SL);
    end;
  end;

end;

procedure FadeBitmap32(ABitmap: TBitmap);
begin

  ABitmap.PixelFormat := pf32bit;

  for var y := 0 to ABitmap.Height - 1 do
  begin
    var SL := PRGBQuad(ABitmap.ScanLine[y]);
    for var x := 0 to ABitmap.Width - 1 do
    begin
      SL.rgbRed := SL.rgbRed div 2;
      SL.rgbGreen := SL.rgbGreen div 2;
      SL.rgbBlue := SL.rgbBlue div 2;
      Inc(SL);
    end;
  end;

end;