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 those small PNG images on to it. Now I have one file instead. Now all I need is to copy one PNG on to other with transparency (btw don't ask why), because I need to work with each image induvidually. I am bad programmer when it comes to working with images. I am using Delphi 7. `PGNImage.Resize` ``` procedure TPngObject.Resize(const CX, CY: Integer); function Min(const A, B: Integer): Integer; begin if A < B then Result := A else Result := B; end; var Header: TChunkIHDR; Line, NewBytesPerRow: Integer; NewHandle: HBitmap; NewDC: HDC; NewImageData: Pointer; NewImageAlpha: Pointer; NewImageExtra: Pointer; begin if (CX > 0) and (CY > 0) then begin {Gets some actual information} Header := Self.Header; {Creates the new image} NewDC := CreateCompatibleDC(Header.ImageDC); Header.BitmapInfo.bmiHeader.biWidth := cx; Heade…

Accepted Answer

Here is one sample code modified from a 'SlicePNG' ("This function slices a large PNG file (e.g. an image with all images for a toolbar) into smaller, equally-sized pictures") procedure found elsewhere:

```
procedure CropPNG(Source: TPNGObject; Left, Top, Width, Height: Integer;
    out Target: TPNGObject);

function ColorToTriple(Color: TColor): TRGBTriple;
  begin
    Color := ColorToRGB(Color);
    Result.rgbtBlue := Color shr 16 and $FF;
    Result.rgbtGreen := Color shr 8 and $FF;
    Result.rgbtRed := Color and $FF;
  end;

var
   X, Y: Integer;
   Bitmap: TBitmap;
   BitmapLine: PRGBLine;
   AlphaLineA, AlphaLineB: pngimage.PByteArray;
begin
  if (Source.Width < (Left + Width)) or (Source.Height < (Top + Height)) then
    raise Exception.Create('Invalid position/size');

Bitmap := TBitmap.Create;
  try
    Bitmap.Width := Width;
    Bitmap.Height := Height;
    Bitmap.PixelFormat := pf24bit;

for Y := 0 to Bitmap.Height - 1 do begin
      BitmapLine := Bitmap.Scanline[Y];
      for X := 0 to Bitmap.Width - 1 do
        BitmapLine^[X] := ColorToTriple(Source.Pixels[Left + X, Top + Y]);
    end;

Target := TPNGObject.Create;
    Target.Assign(Bitmap);
  finally
    Bitmap.Free;
  end;

if Source.Header.ColorType in [COLOR_GRAYSCALEALPHA, COLOR_RGBALPHA] then begin
    Target.CreateAlpha;
    for Y := 0 to Target.Height - 1 do begin
      AlphaLineA := Source.AlphaScanline[Top + Y];
      AlphaLineB := Target.AlphaScanline[Y];
      for X := 0 to Target.Width - 1 do
        AlphaLineB^[X] := AlphaLineA^[X + Left];
    end;
  end;
end;
```

Sample call:

```
var
  Png: TPNGObject;
  CroppedPNG: TPNGobject;
begin
  PNG := TPNGObject.Create;
  PNG.LoadFromFile('..	est.png');

CropPNG(PNG, 30, 10, 60, 50, CroppedPNG);
  CroppedPNG.SaveToFile('..\croptest.png');
```

How to copy one PNG from other PNG?

Solution

Problem