On 4 Feb 2009, at 17:28, Fabio Bracci wrote:
>
> This program just produces either a black window if
> Fl_Double_Window::draw( ) is commented out, or a grey one otherwise.
> I'm pretty unsure about how to use fl_copy_offscreen, but maybe my
> mistake is elsewhere ... why don't I get a nice black square in the
> middle of the window?
This amended version does what I *think* you intended? (Word-wrapping
by my email permitting, of course!)
In general, however, I'd caution against deriving from a window type.
If all you need is a "drawing canvas" then deriving from Fl_Box is a
safer bet, and just have a regular Fl_Double_Window as the outer
container widget.
However, if I understand correctly, you specifically want to make a
container widget? You want to render a complete hierarchy of fltk
widgets into the offscreen, not just regular drawing calls? Is that
correct?
I think using Fl_Group as a base to derive from is probably a good
place to start in that case.
Also, it occurs to me that fluid includes a mechanism for capturing
the widgets as they are displayed on screen (for its print
mechanism.) How is that implemented? Perhaps that is relevant to your
problem?
-----------------
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
#include <FL/fl_draw.H>
#include <FL/x.H>
#include <FL/Fl_Double_Window.H>
Fl_Offscreen offscr = 0;
int offscrW = 200;
int offscrH = 200;
void drawOffscreen( Fl_Double_Window *aWin ) {
int x = aWin->x( );
int y = aWin->y( );
int w = aWin->w( );
int h = aWin->h( );
if (!offscr) offscr = fl_create_offscreen( offscrW, offscrH );
fl_begin_offscreen( offscr );
fl_color( FL_BLACK );
fl_rectf( 0, 0, w/2, h/2 );
fl_end_offscreen( );
fl_copy_offscreen( x, y, offscrW, offscrH, offscr, 0, 0 );
}
class MyWin : public Fl_Double_Window {
protected:
void draw( ) {
drawOffscreen( this );
}
public:
MyWin( int a, int b, char const *label = "Fl_Offscreen test" ) :
Fl_Double_Window( a, b, label ) { }
};
int main( ) {
MyWin *aWin = new MyWin( 400, 400, "Fl_Offscreen test" );
aWin->resizable( );
aWin->show( );
return Fl::run( );
}
/* end of file */
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