> I try to create a Fl_Group derived widget, which redirects pixels
> by means of a fl_offscreen buffer for manipulation.
> fl_offscreen works fine, pixel manipulation is fine, but drawing is
> displaced.
Hmm, I dunno - this seems to work OK for me...
// offscreen-scroll.cxx
// fltk-config --compile offscreen-scroll.cxx
#include <FL/Fl.H>
#include <FL/x.H>
#include <FL/Fl_Double_Window.H>
#include <FL/Fl_Group.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Scroll.H>
#include <Fl/fl_draw.h>
/***********************************************************************
******/
static uchar *data_p = NULL;
static Fl_Offscreen offscr = 0;
static int offscrW = 750;
static int offscrH = 750;
/***********************************************************************
******/
class offscreen_group : public Fl_Group {
protected:
void draw( );
public:
offscreen_group(int X, int Y, int W, int H) :
Fl_Group(X,Y,W,H) { }
};
void offscreen_group::draw() {
int wo = w();
int ho = h();
if (!offscr) offscr = fl_create_offscreen(offscrW, offscrH);
if(!offscr) return; // create must have failed!
fl_begin_offscreen(offscr);
// draw the widget hierarchy of this group into the offscreen
Fl_Group::draw();
fl_end_offscreen();
// copy the offscreen back onto this window...
fl_copy_offscreen(0, 0, wo, ho, offscr, 0, 0);
}
/***********************************************************************
******/
int main(int argc, char **argv) {
Fl_Double_Window *main_win = new Fl_Double_Window(450, 430,
"Fl_Offscreen group test");
main_win->begin();
Fl_Scroll *scroller = new Fl_Scroll(0,0,400,400);
scroller->begin();
offscreen_group *osg = new offscreen_group(0, 0, offscrW,
offscrH);
osg->begin();
osg->box(FL_FLAT_BOX);
int a = 40, b = 40;
// Put some widgets in the offscreen_group
Fl_Button *b0;
while ((a + 60) < offscrW)
{
b0 = new Fl_Button( a, b, 60, 60, "BUTTON");
a += 60;
b += 60;
}
osg->end();
scroller->end();
main_win->end();
main_win->resizable(scroller);
main_win->show(argc, argv);
return Fl::run( );
}
/* end of file */
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