[fpc-pascal] Does FCL Image support transparency?

[Mattias Gaertner]

On Fri, 16 Sep 2016 17:48:33 +0200 (CEST)
Michael Van Canneyt <michael at freepascal.org> wrote:

> On Fri, 16 Sep 2016, Reimar Grabowski wrote:
> 
> > Hi,
> >
> > I want to put watermarks on images in a command line application.
> > This doesn't do the trick:
> >
> > ScaledImage:=TFPCompactImgRGBA8Bit.Create(Width, Height);
> > Canvas:=TFPImageCanvas.Create(ScaledImage); // TFPImageCanvas
> > Canvas.StretchDraw(0,0,Width,Height,Image); // Image is TFPCompactImgRGB8Bit
> > Canvas.Draw(0,0,Watermark); // Watermark is an TFPCompactImgRGBA8Bit
> >
> > Watermark is a transparent PNG loaded from disk but the transparency is not respected when drawing it onto ScaledImage.
> >
> > Can FCL Image do this and if not what are my alternatives?  
> 
> It should be able to do this, yes.

TFPCustomCanvas.Draw does not handle Alpha by merging. It simply copies
the pixel.
Is this a bug or by design?


Mattias