Drawing selection rectangles -- rubber-banding
- From: Eduardo M Kalinowski <ekalin bol com br>
- To: gtk-app-devel-list gtk org
- Subject: Drawing selection rectangles -- rubber-banding
- Date: Thu, 21 Jun 2001 21:38:45 -0300
Hi,
In a project I'm working in, I will need to draw rectangles to
select a region. I've tried implementing this in the "scribble" program
of the GTK+ tutorial.
It is almost working (using the right-button (3) for selecting). The
only problem is that sometimes the old rectangle is not erased when a
new selection is started. This happens when the button is pressed and
dragged very quickly.
Since this rubber-banding technic is quite common in several
applications, I wonder if someone could point me how to correctly do
that.
I'm sending attached the modified version of the "scribble" program.
--
Sometimes when you look into his eyes you get the feeling that someone
else is driving.
-- David Letterman
Eduardo M Kalinowski
ekalin bol com br -- **Novo e-mail** **New e-mail**
http://move.to/hpkb
/* example-start scribble-simple scribble-simple.c */
/* GTK - The GIMP Toolkit
* Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#include <gtk/gtk.h>
/* Rubber-bading */
GdkGC *select_gc;
int p1_x = 0;
int p1_y = 0;
int p2_x = 0;
int p2_y = 0;
/* Backing pixmap for drawing area */
static GdkPixmap *pixmap = NULL;
/* Create a new backing pixmap of the appropriate size */
static gint configure_event( GtkWidget *widget,
GdkEventConfigure *event )
{
if (pixmap)
gdk_pixmap_unref(pixmap);
pixmap = gdk_pixmap_new(widget->window,
widget->allocation.width,
widget->allocation.height,
-1);
gdk_draw_rectangle (pixmap,
widget->style->white_gc,
TRUE,
0, 0,
widget->allocation.width,
widget->allocation.height);
return TRUE;
}
/* Redraw the screen from the backing pixmap */
static gint expose_event( GtkWidget *widget,
GdkEventExpose *event )
{
gdk_draw_pixmap(widget->window,
widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
pixmap,
event->area.x, event->area.y,
event->area.x, event->area.y,
event->area.width, event->area.height);
return FALSE;
}
/* Draw a rectangle on the screen */
static void draw_brush( GtkWidget *widget,
gdouble x,
gdouble y)
{
GdkRectangle update_rect;
update_rect.x = x - 5;
update_rect.y = y - 5;
update_rect.width = 10;
update_rect.height = 10;
gdk_draw_rectangle (pixmap,
widget->style->black_gc,
TRUE,
update_rect.x, update_rect.y,
update_rect.width, update_rect.height);
gtk_widget_draw (widget, &update_rect);
}
static void draw_select( GtkWidget *widget,
gint x,
gint y,
gboolean new)
{
GdkRectangle update_rect;
/* Erase */
gdk_draw_rectangle (pixmap,
select_gc,
FALSE,
p1_x, p1_y,
p2_x - p1_x, p2_y - p1_y);
if (!new)
/* Draw */
gdk_draw_rectangle (pixmap,
select_gc,
FALSE,
p1_x, p1_y,
x - p1_x, y - p1_y);
update_rect.x = p1_x;
update_rect.y = p1_y;
update_rect.width = MAX(x - p1_x, p2_x - p1_x) + 1;
update_rect.height = MAX(y - p1_y, p2_y - p1_y) + 1;
gtk_widget_draw (widget, &update_rect);
p2_x = x;
p2_y = y;
}
static gint button_press_event( GtkWidget *widget,
GdkEventButton *event )
{
if (event->button == 1 && pixmap != NULL)
draw_brush (widget, event->x, event->y);
else if (event->button == 3 && pixmap != NULL) {
draw_select(widget, event->x, event->y, TRUE);
p1_x = event->x;
p1_y = event->y;
gdk_pointer_grab(widget->window, TRUE,
GDK_POINTER_MOTION_MASK,
widget->window,
NULL, GDK_CURRENT_TIME);
}
return TRUE;
}
static gint button_release_event( GtkWidget *widget,
GdkEventButton *event )
{
if (event->button == 3 && pixmap != NULL) {
gdk_pointer_ungrab(GDK_CURRENT_TIME);
}
return TRUE;
}
static gint motion_notify_event( GtkWidget *widget,
GdkEventMotion *event )
{
int x, y;
GdkModifierType state;
if (event->is_hint)
gdk_window_get_pointer (event->window, &x, &y, &state);
else
{
x = event->x;
y = event->y;
state = event->state;
}
if (state & GDK_BUTTON1_MASK && pixmap != NULL)
draw_brush (widget, x, y);
else if (state & GDK_BUTTON3_MASK && pixmap != NULL)
draw_select(widget, x, y, FALSE);
return TRUE;
}
void quit ()
{
gtk_exit (0);
}
int main( int argc,
char *argv[] )
{
GtkWidget *window;
GtkWidget *drawing_area;
GtkWidget *vbox;
GtkWidget *button;
GdkColor red = { 0, 0, 0xFFFF, 0xFFFF };
gtk_init (&argc, &argv);
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_widget_set_name (window, "Test Input");
vbox = gtk_vbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (window), vbox);
gtk_widget_show (vbox);
gtk_signal_connect (GTK_OBJECT (window), "destroy",
GTK_SIGNAL_FUNC (quit), NULL);
/* Create the drawing area */
drawing_area = gtk_drawing_area_new ();
gtk_drawing_area_size (GTK_DRAWING_AREA (drawing_area), 200, 200);
gtk_box_pack_start (GTK_BOX (vbox), drawing_area, TRUE, TRUE, 0);
gtk_widget_show (drawing_area);
/* Signals used to handle backing pixmap */
gtk_signal_connect (GTK_OBJECT (drawing_area), "expose_event",
(GtkSignalFunc) expose_event, NULL);
gtk_signal_connect (GTK_OBJECT(drawing_area),"configure_event",
(GtkSignalFunc) configure_event, NULL);
/* Event signals */
gtk_signal_connect (GTK_OBJECT (drawing_area), "motion_notify_event",
(GtkSignalFunc) motion_notify_event, NULL);
gtk_signal_connect (GTK_OBJECT (drawing_area), "button_press_event",
(GtkSignalFunc) button_press_event, NULL);
gtk_signal_connect (GTK_OBJECT (drawing_area), "button_release_event",
(GtkSignalFunc) button_release_event, NULL);
gtk_widget_set_events (drawing_area, GDK_EXPOSURE_MASK
| GDK_LEAVE_NOTIFY_MASK
| GDK_BUTTON_PRESS_MASK
| GDK_BUTTON_RELEASE_MASK
| GDK_POINTER_MOTION_MASK
| GDK_POINTER_MOTION_HINT_MASK);
/* GC for selection rectangle */
gtk_widget_realize(drawing_area);
select_gc = gdk_gc_new(drawing_area->window);
gdk_colormap_alloc_color(gdk_colormap_get_system(), &red,
FALSE, TRUE);
gdk_gc_set_foreground(select_gc, &red);
gdk_gc_set_function(select_gc, GDK_XOR);
/* .. And a quit button */
button = gtk_button_new_with_label ("Quit");
gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);
gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
GTK_SIGNAL_FUNC (gtk_widget_destroy),
GTK_OBJECT (window));
gtk_widget_show (button);
gtk_widget_show (window);
gtk_main ();
return 0;
}
/* example-end */
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