Re: How to realize a battery-indicator with a trayicon? How to show the current capacity

["Freddie Unpenstein" <fredderic excite com>]

From: "Rorschach", on 17/11/2008 03:54 :

> I wanna write a little battery-indicator in C with GTK. It's already working
> nicly in the console and I know how to write a trayicon with gtk but what
> I don't know is: how can I show the current capacity of the battery? I mean
> shall I do 100 pictures (1-100%) and if the capacity changes just show
> the corresponding new picture? This is imo a bad solution because I have
> to ship 100 pictures with my application.

I can't imagine the images being too large to ship a hundred of them.  Unless you're expecting someone to be 
using it on a full-screen sized widget.


> But how else can I realize this? Painting the image on-the-fly? Just showing the battery and painting it's 
> content on-the-fly?

The combination approach is something I've used a number of times.  Ship the battery graphic, and graphics of 
any ornaments you might need, at appropriate sizes, and then overlay the battery level using any of many 
methods.  The ones I've used are;

1) Include 100 level images (although simply having as many as the number of pixels you're expecting it to be 
in height is enough) of just the guage itself.  This is only needed if the body of the guage image changes 
somehow, like an edge or inner glow or something that can't be achieved to stretching.  (I only had five 
images when I did this, but they were 98x98 pixels each)

2) Paint the guage onto the resized/prepared battery image.  You can get a little bit creative here to keep 
it looking nice, by mixing your paint colour with the existing image.  If you have an alpha channel you're 
not using, for example, the guage can be a flat colour "behind" the base image, and compositing will let 
"glass" type look show through.  You can also ship a second image with just the guage portion, and paint that 
before applying it to the base image, again, over or under depending on your needs, and with or without 
stretching.

3) A trick I've used in one project, was to draw a short "near empty" indicator graphic, and split it into 
two caps.  The middle was simply filled with the bottom row of pixels of the upper cap.  And by drawing it in 
black and white, I could do the relatively expensive manual colouring work at load-time to produce three 
coloured versions in memory from the one image on disk.  It was then just a matter of splicing the images 
together over top of the base graphic as needed (mildly tedious but quite doable).


Good luck.


Fredderic


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