Re: reuse image.display() window?

On Mon, 27 Nov 2017, Robert H. Olsen wrote:

>
> Is there a way to use GraphicsMagick to display an Image, but somehow retain 
> control of the display window so that subsequent images can be displayed in 
> the same window?
>
> For example, if I have images being acquired at, say, 1 hz is there some way 
> that I can overwrite/replace the older image in the same window when a new 
> one arrives using GraphicsMagick?
>
> The display() function for an image object works fine for a single image, but 
> the user must close the window.
>
> I found references to functions like MagickXPasteImage in display.h but 
> couldn't determine if that might be useful to me, or how that might be used.

It is likely that the necessary code exists but it might not be 
accessible.

A ready-made way to accomplish this is by using the 'gm display' 
utility as a co-process.

Start 'gm display' as a background process (gm display &).  Then run

   gm display -remote filename

to cause the displayed image to be reloaded based on filename 
(unfortunately requires that a file be written).  This command will 
return as soon as the request has been sent.  This is using X11 for 
the communication to send the command.  As a result, there can only be 
one such window per X11 server unless perhaps via some X11-specific 
mechanism.

If you don't want a progress indicator while the image is loading, 
then start the background process like

   gm display +progress &

If your images were all 512x512 then you could do

   gm display +progress -size 512x512 xc:black &

and then the initial image would be a black window which is replaced 
with the first image which is loaded.  As an alternative, you could 
start the background program with your first image file and then 
reload it after that.

If you are creating a slide-show, then it is important not to send 
update requests faster than the image can reasonably be displayed.  I 
don't know if 1 HZ rates are possible, but it would depend on the 
dimensions of your image and the intermediate format used.

The functionality of 'gm command' is available in the GraphicsMagick 
library.  There are prototypes for 'GMCommand()' (any GraphicsMagick 
utility command) and 'DisplayImageCommand()' declared in 
magick/command.h.  This means it is possible to avoid executing an 
external 'gm' utility (particularly to refresh the image) but the 
program which displays the image still needs to be a co-process.

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot