[no subject]

[Markus Müller <markus mueller gersys de>]

Hello list,
 
let me just give a short introduction to myself before i get to the point...
I´m with Gersys, a small company producing embedded platforms for railway applications ( you may look at 
www.gersys.de).
In generel our products are small embedded pc´s running winXPe or linux in very rough environments. Normally 
our customers get a device running the OS and are writing their own applications.
I´m an developer of Hard- and Software and an electrical engineer. My background regarding software 
development for now is in first instance uC-Code in C, but i´ve also done some example applications under 
Windows/.NET/VisualStudio/C# for some graphical UI´s...
 
For our new project we have for the first time the task of programming a application:
Our customer installs several networking cameras along some city-trains. Our device has to get up to four 
video streams an display them (which is not the problem for now, maybe later ;-) )
The train driver has to be given the possibility of choosing which camera(s) he wants to view. Therefore, and 
now we get to the point, we have to display a symbolical image of the train which represents the number and 
position of the cameras and realize a navigation by key inputs through them. The predefined picture shows for 
example a train with three combined vehicles, each consisting of four/six waggons. The waggons have up to 
four inner cameras and up to two outer cameras, which are reprepesented by some pie-slice-like symbols 
(gdk_draw_arc()...). The selected camera(s) are highlighted by some color. An event from a navigation key 
moves the selection to the next set. The composition of the train may vary and has to be loaded at program 
start, so the displayed selection image has to be created dynamically.
 
Our developing platform is a Suse10.3-machine with Eclipse-Environment. The project is written in C and we 
use GTK2. Because of the above mentioned structure we have a very object-orientated approach, but due to 
compatibility/porting-issues we don´t want(ed) to use gtkmm (perhaps to be discused) for now. (The 
destination target is running eLinOS/Codeo-Environment/X-Server...)
 
I´ve "played" a lot the last week and got some few satisfying results: The drawing of the train using 
standard widgets and gdk-functions has already the lookalike of the predefined image. Creating a simple 
widget for drawing a camera symbol and manipulating the color of it was also succesful.
 
The main question for now i´d like to hear your opinion to is about the data structure of the project. My 
approach in cause of the resent results is following:
Creating low level widgets (e.g. the camera symbol, a waggon...) with the necessary data variables (e.g. 
color, name...), which can be manipulated by the "top level program part" (the one which knows what is 
selected etc. ...)
The widgets will be nested: The train-widget provides a array of vehicles which provides a array of waggons 
with an array of cameras...
Accessing the object properties can be done with references/pointers to the data variables (the "normal" 
access to struct-members e.g.: train.vehicle[1].waggon[4].camera[3].colour = green)
One of the biggest questions therefore is the structure of the necessary manipulating functions: How can i 
best handle e.g. the redrawing of a camera when its de-/selected (In C++ i would create a member-function to 
the camera-object!?). I think to create a function set for every widget which can always provide the 
interface for the upper "parent" instance!? Alternative there could be a set of "top level" functions, but 
therefore the parameters are getting kind of nasty !?
 
I hope i delivered enough information in this vast of text to provide an overview to my problem(s) and hope i 
get some opinions to my approaches from you to start a productive discussion about it!
 
Best regards
Markus
 
-----
Gersys GmbH, Hans-Urmiller-Ring 46c, D-82515 Wolfratshausen, Germany
Geschaeftsfuehrer: Erwin Sterzer, HRB 137 872 Muenchen, Fon: +49(0)8171 9986-6
 
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