> > I think you might be able to make your approach work by starting the
> > offscreen, then clearing your boolean and directly calling
> the widget
> > ::draw() method again.
> > Then, when that returns, reset the boolean and end the offscreen.
> > Well, maybe that can work.
>
> Well, I was trying exactly this, to trigger draw() at the
> group widget holding the complex structure, but I get a weird
> compile error ...
Hmm, odd. I would expect (but have not tried) that the draw method
should be able to recursively call itself in that case. I wonder why it
fails?
Might be worth posting the error message you get, someone might know
what it pertains to.
> Thanx! I couldn't figure it out.
> btw, int X, int Y, are the coordinates where fl_read_image
> starts to read and int W, int H are the width and height, I
> suppose ... documentation bug?
> well, this will be the pixmap then. but what is it then a
> Fl_Offscreen variable? this is just typed as ulong, I can't
> figure out its real meaning
Here's a worked example... CAUTION: This WILL NOT actually work, as it
assumes the existence of my PNG helper library to write the grabbed data
to a PNG file, so you'll need to substitute your own data storage
mechanism in place of that.
(Provide a function to replace my write_png() function )
--------------
// offscreen-grab.cxx
// fltk-config --compile offscreen-grab.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>
// #include "write_png.h"
Fl_Offscreen offscr = 0;
int offscrW = 750;
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);
}
/***********************************************************************
******/
uchar *data_p = NULL;
static void cb_bt_grab(Fl_Button*, void*)
{
if(offscr) { // offscreen exists, grab something
if(data_p){
delete[] data_p;
data_p = NULL;
}
fl_begin_offscreen(offscr); /* Open the offscreen
context for reading */
data_p = fl_read_image(data_p, 0, 0, offscrW, offscrH,
0);
// write_png("Test2.png", data_p, offscrW, offscrH, 3,
"meta-data", "comment");
fl_end_offscreen(); // close the offscreen context
}
} // cb_bt_grab
/***********************************************************************
******/
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_Button *grab_bt = new Fl_Button(405, 405, 40, 20, "Grab");
grab_bt->callback((Fl_Callback*)cb_bt_grab);
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;
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 */
----------
Ian
SELEX Sensors and Airborne Systems Limited
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14
3EL
A company registered in England & Wales. Company no. 02426132
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