Re: [fltk.general] Suggestion for Point selector widget Fl_Point - Forums

On Tuesday, 19 October 2021 at 19:16:33 UTC+1 erco wrote:

On 10/19/21 11:00 AM, anmol wrote:

I am trying to create a widget that can be pointed into a box to select the pixel co-ordinates within. It has a click box next to it to activate the point selection crosshairs, and then the point co-ordinates inside the box will be selected.

Any suggestions ?

    I'd suggest deriving a widget from Fl_Group that implements this pixel coordinate picking
    behavior, handle() to track the mouse movement. If I remember correctly, in response to
    FL_ENTER, return 1 so your widget gets FL_MOVE events, which gives tells you where the
    mouse is whenever it moves. Save the x/y coords from FL_MOVE in your widget and trigger
    a redraw() so that your draw() routine can draw() the crosshairs over the child widget.

Or you can probably use ::belowmouse() to figure out the co-ordinates even relative to non-child widgets too, I think.

Hmm, testing

OK, example follows. Seems to work.

* fltk-config --compile track-cursor.cxx

/* Standard headers */

#include <stdlib.h>

/* Fltk headers */

#include <FL/Fl.H>

#include <FL/Fl_Double_Window.H>

#include <FL/platform.H>

#include <FL/Fl_Box.H>

#include <FL/Fl_Button.H>

#include <FL/Fl_Value_Output.H>

#include <FL/fl_draw.H>

// constants to define the view etc.

static const int win_size = 512;

// Output the mouse (x,y)

static Fl_Value_Output *valx = NULL;

static Fl_Value_Output *valy = NULL;

/*****************************************************************************/

class tracker_win : public Fl_Double_Window

{

public:

tracker_win (int W, int H, const char *L = 0)

: Fl_Double_Window(W, H, L) {

}

private:

int handle(int event);

};

// Event handling

int tracker_win::handle(int ev) {

int res = Fl_Double_Window::handle(ev);

switch (ev) {

case FL_MOVE:

{

int X = Fl::event_x();

int Y = Fl::event_y();

Fl_Widget *tgt_widget = Fl::belowmouse ();

int xw = tgt_widget->x();

int yw = tgt_widget->y();

int dx = X - xw;

int dy = Y - yw;

if (this == tgt_widget) {

dx = X;

dy = Y;

}

valx->value(dx);

valy->value(dy);

}

res = 1;

break;

default:

break;

}

return res;

} /* end of handle() method */

/*****************************************************************************/

static tracker_win *main_window = 0;

/*****************************************************************************/

// Quit button callback (closes the window)

void quit_cb(Fl_Button *b, void *) {

main_window->hide();

}

/*****************************************************************************/

int main(int argc, char **argv)

{

main_window = new tracker_win(win_size, win_size, "Mouse tracking demo");

main_window->begin();

main_window->box (FL_FLAT_BOX);

Fl_Box *dummy_box = new Fl_Box (10, 10, 100, 100);

dummy_box->box (FL_BORDER_BOX);

Fl_Box *other_box = new Fl_Box (220, 220, 100, 100);

other_box->box (FL_DOWN_BOX);

valx = new Fl_Value_Output (130, 10, 40, 20, "X");

valx->box (FL_THIN_DOWN_BOX);

valy = new Fl_Value_Output (190, 10, 40, 20, "Y");

valy->box (FL_THIN_DOWN_BOX);

Fl_Button *quit_bt = new Fl_Button (10, 472, 60, 30, "Quit");

quit_bt->box(FL_THIN_UP_BOX);

quit_bt->callback((Fl_Callback *)quit_cb);

main_window->end();

main_window->resizable(main_window);

main_window->show(argc, argv);

return Fl::run();

} // main