Zoom in einem Canvas - Feld

[Bummi]

unter verwendung von GDI+ (free)
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mit sehr guten Ergebnissen

Delphi-Quellcode:

uses   GDIPAPI,  GDIPOBJ;



Procedure ScaleImage(Const source,dest:String;DestWidth,DestHeight:Integer;Qual:Integer=92;WithOutMargins:Boolean=false;BgColor:TColor=ClWhite);
var
  HDCImage:TImage;
  graphics : TGPGraphics;
  image: TGPImage;
  width, height: Integer;
  faktor:Double;
  destx,desty:Double;
  Ext:String;
begin

  Ext := UpperCase(StringReplace(ExtractFileExt(dest),'.','',[]));
  image:= TGPImage.Create(source);
  width  := image.GetWidth;
  height := image.GetHeight;
  if (DestWidth / width) < (DestHeight/Height) then faktor  := (DestWidth / width) else faktor:= (DestHeight/Height);
  HDCImage:=TImage.Create(nil);
  if WithOutMargins then
    begin
    HDCImage.Width  :=  Trunc(faktor * width);
    HDCImage.Height :=  Trunc(faktor * height);
    destx :=  0;
    desty :=  0;
    end
  else
    begin
    HDCImage.Width:=DestWidth;
    HDCImage.Height:=DestHeight;
    destx :=  (DestWidth - faktor * width) / 2;
    desty :=  (DestHeight - faktor * Height) / 2
    end;
  if BgColor<>clWhite then
    begin
      HDCImage.Canvas.Brush.Color:=BgColor;
      HDCImage.Canvas.Fillrect(Rect(0,0,HDCImage.Width,HDCImage.Height));
    end;
  graphics := TGPGraphics.Create(HDCImage.Canvas.Handle);
  graphics.SetInterpolationMode(InterpolationModeHighQualityBicubic);
  {
  rct.x :=  destx ;
  rct.Y :=  desty * 1.0;
  rct.Width := faktor * width;
  rct.Height  := faktor * height;
  graphics.SetClip(rct);
  }
  graphics.DrawImage(
    image,
    MakeRect(destx,  desty , faktor * width, faktor * height),  // destination rectangle
    0, 0,        // upper-left corner of source rectangle
    width,       // width of source rectangle
    height,      // height of source rectangle
    UnitPixel);
  image.Free;
  HDCImage.invalidate;
  ForceDirectories(ExtractFilePath(dest));
  if ext = 'BMP' then HDCImage.Picture.Bitmap.SaveToFile(dest)
  else SaveBMPasJPG(dest,HDCImage.Picture.Bitmap,qual);
  graphics.Free;
  HDCImage.Free;

end;