On 2 Feb 2009, at 19:39, Greg Ercolano wrote:
>> Thanx, I will look into the fl_offscreen; are there any
>> examples/code snippets here on the site?
>
> I just grepped the fltk 1.3.x 'FL' directory; looks like
> the functions are:
>
> fl_create_offscreen(w,h)
> fl_begin_offscreen(pixmap)
> fl_end_offscreen()
> fl_copy_offscreen(x,y,w,h,pixmap,srcx,srcy)
> fl_delete_offscreen(pixmap)
>
> I don't think they have docs yet.
>
> My guess is you bracket your regular fltk drawing code
> with fl_begin_offscreen() and fl_end_offscreen(), and the
> pixels will go into ram instead of a window.
Yes, what Greg says.
Also, note that unlike "regular" fltk drawing, if you make your
offscreen "current" by calling fl_begin_offscreen(pixmap) then you
can draw to it *at any time* - not just within a fltk draw context,
so this is different and sometimes more convenient than the usual
fltk way of handling the drawing.
Note also that you have to have *at least* one window mapped before
you create your first offscreen context, because it uses the mapped
window to ascertain the correct rendering properties. I'm not sure if
that is documented or anything, it is just what I discovered trying
to use them...
So you show your main window, then sometime later you create the
offscreen...
pixmap = fl_create_offscreen(w,h)
Then later when you want to draw:
fl_begin_offscreen(pixmap)
(fltk drawing calls)
fl_end_offscreen()
Then when you want to show part of the offscreen in your view
fl_copy_offscreen(x,y,w,h,pixmap,srcx,srcy)
inside the ::draw() method of your view widget to blit a rectangle
from the offscreen onto your view.
That's about it, at a very high level, anyway.
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