Goal of this short guide is to slightly improve experience with an old DirectX/Glide games without destroying their original look.

Disclaimer:
! It's not gonna work properly with ALL games in existence.
! Your GPU must support DX12.

We are gonna get:
> DirectX 12 for compatibility with modern operating systems.
> SMAA - Good looking antialiasing that has very little impact on resources (https://iryoku.com/smaa/)
> CAS - Adaptive sharpening that unblur the textures in a very nice way (https://gpuopen.com/fidelityfx-cas/)

D3D12 translation
Game will behave much better under Win10+ (i.e Alt+Tab and OSDs most likely gonna work properly), also it's required to get ReShade working.

1. Download/Install latest stable version of dgVoodoo (http://dege.freeweb.hu/dgVoodoo2/dgVoodoo2/)
If you game is 32bit (most likely):
Copy dgVoodooCpl.exe, dgVoodoo.conf and everything from MS\x86\ to the root game directory.
Otherwise copy files from MS\x64\.

2. Configuration (dgVoodooCpl.exe):
x Select [General] Output API: Direct3D 12

3. Check that your game runs properly with dgVoodoo.

SMAA + FidelityFX Contrast Adaptive Sharpening (CAS)
Let's get decent antialiasing with adaptive sharpening using ReShade.

1. Download/Install ReShade (https://reshade.me)
x Select your game executable
x Select Direct3D 10/11/12 API
x Select Standard and SweetFX packages

2. Configuration
-> Run Game
-> Hit Home key
-> Enable CAS.fx and SMAA.fx processors

Gave it a go with Kohan and much to my surprise the dgvoodoo program was exactly what i needed to get it working, did add the reshaders too just for fun and while it worked it does not provide any other effect

After this i decided to see if i could RRT2 working with voodoo too but that one needed another approach. There is an unofficial patch which needed to be installed. Thank god the Gog made patch also worked for the steam version. Some dude also created a new wrapper changing the output to openGL which resulted in a very fine operation for this game

SMAA and CAS processing is quite subtle on default settings.
You should just get smother edges on dynamic objects and slight sharpness increase on static.
But since Kohan is 2.5D the overall effect is probably barely noticeable.