Incorrect painting on png image loaded from file
lazarus / 39-Graphics

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wp · 2012-12-20 15:04

Suppose I want to paint a red rectangle onto the canvas of a png
graphic. The graphic is loaded from the attached file. But the image
into which the modified png is copied shows only a punched-out
rectangle. I tried various different approaches, but don't find the
clue.

The issue seems to be related to this particular file. When I am using
png files that I saved from screenshots the program has normal
behaviour..

 I am using the following code to load and modify the png file and to
show it in a TImage component:

Code: [Select]procedure TForm1.FormCreate(Sender: TObject);
var
  png: TPortableNetworkGraphic;
begin
  png := TPortableNetworkGraphic.Create;
  try
    png.LoadFromFile('test.png');
    png.Canvas.Brush.Style := bsSolid;
    png.Canvas.Brush.Color := clRed;
    png.Canvas.Rectangle(100, 100, 200, 200);
    Image1.Picture.Assign(png);
  finally
    png.Free;
  end;
end;
      

What is wrong?