Albrecht Schlosser wrote:
To the x/y translations: You must be aware that the offscreen works
like a full window, and that the child draw() methods add their
x/y coordinates to draw at the correct positions. However, the
scroll mechanism can add *negative* offsets to the widgets, so that
they are positioned more to the left and top. That's why I suggested
to resize() the Fl_Canvas to (0,0) temporary, and to set the scrollbars
to their initial position (0,0) as well.
see appended file capture_v2.cxx ;-)
Enjoy !
Albrecht
/*
This demo program captures the contents of an Fl_Scroll in an
Fl_RGB_Image. The image is then shown in another window.
This version works independent of current scrollbar positions.
Warning: There's NO CLEANUP, don't use this for production code !
Compile and link with (use FLTK 1.3.x):
fltk-config --compile capture.cxx
*/
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <FL/Fl.H>
#include <FL/x.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Scroll.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_RGB_Image.H>
#include <FL/fl_draw.h>
class Fl_Canvas : public Fl_Scroll {
public:
Fl_Canvas(int X, int Y, int W, int H, const char *L=0);
Fl_RGB_Image *capture();
};
Fl_Canvas::Fl_Canvas (int X, int Y, int W, int H, const char *L)
: Fl_Scroll (X,Y,W,H,L) {}
Fl_RGB_Image* Fl_Canvas::capture()
{
if(children() <= 2)
return NULL;
// save original position, size, and scrollbar positions
int xx = x(), yy = y(), ww = w(), hh = h();
int xp = scrollbar.value(), yp = hscrollbar.value();
// Determine the full (unscrolled) size of the canvas area
int xdim = w();
int ydim = h();
if(hscrollbar.visible())
xdim += (int)hscrollbar.maximum();
if(scrollbar.visible())
ydim += (int)scrollbar.maximum();
window()->make_current();
// setup the offscreen buffer
Fl_Offscreen offscr = fl_create_offscreen(xdim, ydim);
// force children to draw into the offscreen buffer
fl_begin_offscreen(offscr);
fl_color(color());
fl_rectf(0,0,xdim,ydim); // draw background
resize(0,0,xdim,ydim); // fix relative position
scroll_to (0,0); // fix child positions
redraw(); // make it really draw
// Note: resize() also fixes the scrollbar positions,
// i.e. the last 2 children are the scrollbars now.
// (You could also test for &scrollbar and &hscrollbar !)
for (int i=0; i<children()-2; i++) { // without scrollbars
Fl_Widget *o = child(i);
o->draw();
}
// Annotate the image...write on the image
fl_rectf(100, 100, 150, 100, FL_BLACK);
fl_color(FL_WHITE);
fl_font(FL_TIMES, 15);
fl_draw("Hello, World!", 125, 125);
// read the image back...
uchar *offscreenImage =
fl_read_image(0, 0, 0, xdim, ydim);
fl_end_offscreen();
// Pack a Fl_RGB_Image and force its dtor to do the cleanup
Fl_RGB_Image *rgb_img = new Fl_RGB_Image(offscreenImage,xdim-x(),ydim-y(),3);
rgb_img->alloc_array = 1;
// restore position, size, and scrollbars
resize(xx,yy,ww,hh);
scroll_to(xp,yp);
redraw(); // just to be sure
return rgb_img;
}
static Fl_Canvas *canvas = 0;
static void button_cb (Fl_Widget *, void *) {
Fl_RGB_Image *img = canvas->capture();
if (img && img->w()>0 && img->h()>0 && img->d()>0) {
Fl_Window *tw = new Fl_Window (img->w(),img->h(),"captured image");
Fl_Box *b = new Fl_Box(0,0,img->w(),img->h());
b->box(FL_FLAT_BOX);
b->image(img);
tw->end();
tw->show();
}
}
int main (int argc, char **argv)
{
Fl_Window *win = new Fl_Window (800,600,"capture test");
canvas = new Fl_Canvas (100,100,600,400);
canvas->box(FL_DOWN_BOX);
Fl_Box *box1 = new Fl_Box (100,100,100,100,"Box 1");
box1->color(FL_RED);
box1->box(FL_FLAT_BOX);
box1->align(FL_ALIGN_INSIDE|FL_ALIGN_CENTER);
Fl_Box *box2 = new Fl_Box (650,450,100,100,"Box 2");
box2->color(FL_YELLOW);
box2->box(FL_FLAT_BOX);
box2->align(FL_ALIGN_INSIDE|FL_ALIGN_CENTER);
canvas->end();
Fl_Button *button = new Fl_Button (20,520,60,30,"capture");
button->callback(button_cb);
win->end();
win->show(argc,argv);
return Fl::run();
}
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