RE: Making a cursor (cross hair) track between image displays

["Tilton, James C. (GSFC-6063)" <james c tilton nasa gov>]

Thanks John,



Your response is very helpful. The one key question that remains for me is:



How do I draw a "floating crosshair"?



Thanks.


Jim
________________________________
Dr. James C. Tilton                                                Voice:   301-286-9510
NASA Goddard Space Flight Center                   FAX:     301-286-1776
Mail Code 606.3                                                    E-Mail:  James C Tilton nasa 
gov<mailto:James C Tilton nasa gov>
(Computational & Information Sciences and Technology Office)
Greenbelt, MD 20771
URLs:      http://ipp.gsfc.nasa.gov/ft_tech_rhseg.shtm and http://science.gsfc.nasa.gov/606.3/TILTON/




-----Original Message-----
From: jcupitt gmail com [mailto:jcupitt gmail com]
Sent: Wednesday, April 04, 2012 4:00 AM
To: Tilton, James C. (GSFC-6063)
Cc: gtk-app-devel-list gnome org
Subject: Re: Making a cursor (cross hair) track between image displays



Hi Jim,



On 2 April 2012 17:00, Tilton, James C. (GSFC-6063)

<james c tilton nasa gov> wrote:

> When I place the cursor in one of the display images, I would like to have a cross hair appear at the 
> cursor location of the window in which the cursor is placed at the location currently pointed to by the 
> cursor. I would ALSO like to have a similar cross hair appear in each of the other associated display 
> images.



Add an event handler to the eventbox and listen for GDK_MOTION_NOTIFY.

You need to use gtk_widget_add_events() and turn on motion events with

GDK_POINTER_MOTION_MASK, gtk will not deliver motion events to windows

by default to try to cut down on unnecessary signalling.



(gtk used to support motion event compression, where it would just

report the most recent position rather than all positions since the

last event delivery, but I think this has been deprecated ... perhaps

an expert knows)



Once you have a motion events, use motion.x and motion.y to get the

mouse position, map this to image space, then map out to the

coordinate space for your other image windows. On those other

displays, draw a floating crosshair at the right spot.



My program does something like this, you're welcome to look at the

source if it might help. Though it's a large, hairy thing and perhaps

not a clear example.



http://www.vips.ecs.soton.ac.uk/index.php?title=VIPS



John