I think Koen would say is that one of the first things to do is to learn GEF. Second thing would be to get to know the source a little by playing with it.
I tried the latter once without learning GEF since I only wanted to see how difficult it would be to change some small things and that was fairly easy. If you want to change the drawing capabilities (like e.g. snap to grid for the transitions, please...please... ;-)) then GEF is certainly needed
I want to integrate a form designer with jBPM process designer. and generate jsp file automatically. though jBPM4jsf have done this. but considering learning curve for jsf, our team don't want to jump into it.
Do u have any ideas? it would be very helpful to me.
yes, do use jsf, but also go for seam. The jBPM console is also going in that direction and the jBPM4jsf might change in the not so distant future (getting more minimal)
I want to "upgrade" the GPD as well. But I don't really want to rewrite the code because I want that my changes will work with future versions of the GPD too. That means I want to develop a plugin which has the GPD as dependency and then want to add some functionality. And now I want to know if it is possible in principle and what do I have to be aware of?
This is possible and some people have done this successfully. It is however not the easiest job. As Ronald suggest, knowledge of Eclipse plugin development and of GEF is a must. The easiest way is to look at the extension points that are currently present in the plugin and see how they are used in the plugin itself. I do eat my own dogfood.
Now the support for extensions can and will be augmented in the future. Probably some of the extension points will have to change, so consider all of them 'private' api and bear with me if something breaks your code.