Sorry I don't fully understand what you mean, so I'll answer a few different aspects.
fpGUI is a 100% custom drawn toolkit. That means fpGUI does all its own painting of all its widgets (controls). The same applies to any events in widgets - fpGUI handles user interaction and generates events without any OS or other toolkit assistance.
If you were referring to creating an fpGUI applications that looks "native" (there doesn't seem to be any OS that only has one look these days).... fpGUI includes 6 or more themes as standard, an many user contributed themes are available too. So with fpGUI you can have any look you want. There are very few limitations, if any at all.
One of the user contributed themes I have see, queries the underlying OS toolkit (Windows, KDE, Gnome) for system colours, then applies that to fpGUI. That theme isn't standard with fpGUI yet (but is under consideration).
Equally, you can create a theme that asks the underlying OS to paint widgets of equal functionality to a memory bitmap, then paint that bitmap in fpGUI. This is not something I am personally interested in, but it has been done in many other toolkits - Qt is probably the most popular example of this.
You could also create a bitmap based theme, where widgets get painted based on supplied bitmap images. I have experimented with this idea, and my work on this can be found in the
<fpgui>/prototypes/ directory. This is actually something I'm interested in added to fpGUI. I have loads of ready made theme sets, consisting of many bitmaps for the most common widgets. There was a old program named "
Pixel Image Editor" (also developed with FPC) that had loads of such bitmap themes. Win95, XP (silver), XP (blue/green), Ubuntu Human, Linux Mint are just some of the looks it could reproduce. Those bitmap themes could be reused for a fpGUI theme too.
If I didn't manage to answer your question, please elaborate as much as possible, and I'll try answering again.
