It was a very tough decision to make. I've grown quite attached to my codebase in 7 years of tinkering in my spare time. As a learning journey, it is how I learnt C# and simultaneously contains the best and the worst C# code I've ever written. As an idea, abandoning that is bittersweet to say the least.
I actually explored the idea of switching to Unity quite a few years ago, but I found the learning curve to be too much and went running back to my comfort zone with my tail between my legs within a month. In hindsight I probably should have perservered with it, but at the time I was evaluating alternative approaches, so switching back was an acceptable outcome. Unity evaluated? Unsuitable? Great, back to work.
This time around, I don't have that luxury. I've painted myself into a corner and I can't see any other way out. I fear that unless I switch to Unity, I will end up abandoning this project due to lack of motivation. The catalyst for this terribly pessimistic thinking is my experiences trying to implement skinned animation in my game engine. I've followed many tutorials, rewritten the skinning a few times, and I actually got as far as having the skinned model rendering correctly... until I tried to animate it and then it all fell apart. *cue sad music*
Basically there's too many quirks in my setup that means no tutorials are directly transferable to my situation. eg: Different matrix representations of DirectX vs OpenGL. Different coordinate axes for animations vs meshes. YUp vs ZUp representations. Each of these would be easy enough to trial and error my way through, but combined, they have been kicking my butt for a couple of months.
Another factor is SlimDX. Back when I started this project, SlimDX was already starting to wane in popularity. Then there's the fact I'm developing against DirectX 9. Back in 2010, that was a bit silly, since it was already 6 years old, but now in 2017, that just seems ludicrous! I'd already resigned myself to the fact that I'd eventually have to add DirectX 11 support, but realistically, when was I going to find time to do that?
So I've decided that I should cut my losses and embrace Unity.
The GoodSo what am I gaining? A fully featured, mature game engine that is graphically superior to anything I could create. Access to a huge number of useful assets on the Unity asset store. Many useful tutorials on a variety of game development topics that are relevant to my exact situation, and don't require messy transpositions. I'm using Unity, they are using Unity. Profit!
The BadWhat am I losing? Pretty much all of the 90,000 or so lines of C# code I've written over the last 7 years. Actually, that's not entirely true, as Unity scripting can be done in C#, so a proportion of the back end code might be able to be re-used.
The UglyOk, so what am I keeping? All the concepts, all the ideas, all the game mechanics and systems that I tested and tweaked should be able to brought across. Everything that makes it a game, rather than a game-engine. There's much, much, more of this that's still in my game design workbooks than in code, so that's an advantage I suppose. If I waited another year before switching I'd be losing more work down the line.
I think I've made peace with the fact that I have to let the codebase go, and starting from scratch is actually not such a bad idea. Over the last few years I've slowly been refactoring my game engine to be more Unity-like in its approach anyway, eg: Using components and a similar User Input system.
One way of looking at it is that what I've created thus far was a prototype. A fairly elaborate prototype that I spent way too much time polishing, but a prototype nonetheless. Now that I have access to better tools I can hopefully make this crazy idea a reality. :|