opengl

[Volutar]

I suggest second option. It will keep gameplay and design fully original-like. With all benefits of 3D, though original game feel and spirit.

[sir_nacnud]

Shaders???  
Excuse me, but what for???
What's wrong with drawing quads with game graphics as textures? Even Z-buffer could be disabled, if tiles will be rendered in proper z-order (as they are at the moment).

"Texture sheet" actually called texture atlas, and can be used with classic quad-rendering tech. These atlases have to be built at graphics loading stage, because one GPU supports 4096x4096 texture maximum, another - 1024x1024, pre-building isn't an option. And... no need of massive texture transfer each frame!!!


Gosh...

Going shaders will instantly kill possibilitiy of porting application to other platforms, like ios or android...

iOS supports OpenGL ES 2.0 which supports a programmable pipeline (shaders) in addition to a fixed pipeline.  I don't know about Android, but I think it's phone dependent.

With the current version of OpenGL, 4.2, the programmable pipeline is the preferred method.  Most of the fixed pipeline functions are deprecated.  I'm not saying OpenXcom should use a shader based rendering method, just mentioning that it shouldn't be written off, as it is the current method for 3D graphics.

[Volutar]

OpenGL version 4 isn't all-around. Quite a lot of devices are unable to support 4.x while supporting 2.0 or 1.6. I myself have XP with NVidia drivers 1xx.xx and limited to OGL2.0 and suffer from unnecessary driver requirements.

OpenGL2.0 is more than enough. Term "deprecated" should be deprecated!! Backward compatibility is very important, so minimum system/driver requirements should be maintained.

[Yankes]

https://projectzomboid.com/blog/index.php/2011/04/isometric-development/
interesting post about creating iso-game using opengl and solving some problems with it.

[Volutar]

Project zomboid! nice survival game.

[Volutar]

I'd like to remind you about game "Sacred" which utilizes nice 2d landscape pixel-accurate graphics, and 3d units.

Why 2d landscape?
- Because there is no need to constantly rotate everything.
- Because 2d graphics could look much crisper and detailed, though retaining very low requirements.

Why 3d units?
- Because 2d units will be most disk/memory-consuming entities considering enormous number of armor/weapon/action combinations. 3d units are much efficient.
- Because animation could be much smoother (Why do you think diablo2 heroes have such "jagged" animation?).

Same approach could be used for next-gen xcom-like game. Such hybrid engine probably will be acceptable even for mobile platforms.