The SDK is needed for 1. and 3. (only for full access / completly new HUD elements, basics are already possible without the SDK)
You also need to know the basic MOD structure, which is explained HERE and HERE.
CryEngineÂ² features: LINK (PDF)
What kind of applications you have to use to create new features for your MOD:
- C++: Visual Studio 2005 (Game DLL compilation / compiling with free tools similar to THIS should be possible, but it's not tested at the moment)
That's the most complex and difficult part to add new features for any kind of modification. But you also have the most flexibility.
Difficulty: 5/5 (depends on your knowledge base)
- Lua: 5.1
Basic modifications should be first added here. Especially for AI scripting.
Editor (freeware): Notepad++, PSPad, ConTEXT, Crimson, Vim
The Lua-Scripts are located here: ../CrysisRootFolder/GameData.pak (open with WinRAR)
Inside the pak-file: ../Scripts
Difficulty: 3/5 (depends on your knowledge base)
- HUD/UI: normal Flash Actionscript 2.0 + Scaleform optimization (.gfx format)
If you want to add new HUD/UI elements you have to realize it with Flash + Actionscript (UI elements should also need the Scaleform SDK).
You have to use C++ (custom Game DLL) to show your new elements ingame.
You can find all .gfx files here: ../CrysisRootFolder/GameData.pak (open with WinRAR)
Inside the pak-file: ../Libs/UI
Difficulty: 2/5 (depends on your knowledge base)
NOTE: UNOFFICIAL INFORMATIONS (do not blame Crytek for any wrong information)
The SDK does not currently have a release date, so please dont ask when it will be out.