How to copy one PNG from other PNG?

Question

My application needs a lot of PNGs and I often mess up my code while trying to work with them. To make my life easier I made one big PNG image in Realword Paint and pasted all t

Answer 1

Here is another version (It works very fast):

procedure CropPNG(Source: TPNGObject; Left, Top, Width, Height: Integer;
  out Target: TPNGObject);
var
  IsAlpha: Boolean;
  Line: Integer;
begin
  if (Source.Width < (Left + Width)) or (Source.Height < (Top + Height)) then
    raise Exception.Create('Invalid position/size');

  Target := TPNGObject.CreateBlank(Source.Header.ColorType, 
    Source.Header.BitDepth, Width, Height);
  IsAlpha := Source.Header.ColorType in [COLOR_GRAYSCALEALPHA, COLOR_RGBALPHA];
  for Line := 0 to Target.Height - 1 do
  begin
    if IsAlpha then
      CopyMemory(Target.AlphaScanline[Line], 
        Ptr(LongInt(Source.AlphaScanline[Line + Top]) + LongInt(Left)), 
        Target.Width);
    CopyMemory(Target.Scanline[Line], 
      Ptr(LongInt(Source.Scanline[Line + Top]) + LongInt(Left * 3)), 
      Target.Width * 3);
  end;
end;

Note: The above code is compatible with the newer pngimage Version 1.56+ (which supports the CreateBlank constructor)