This last week-end, I have learned GLSL, so now I should be able to create simple shaders to be used in the game.
The very first one I made is some kind of a RGB Split effect, just like on the title screen (although, the effect on the title screen is faked by using 4 sprites, the base sprite, and 3 for the R, G, and B channels). I still don't know how it will be used in the game, but it will :)
The second one is an outline shader I made to replace the old system that consisted in using a second sprite that was displayed under the weapon to make it look like it has an outline. With the old system I had to create a second version of each weapon sprite and modify it with an image editor. Now it's a lot more simple!
And finally, there's this "hologram" effect, I was inspired by what Black Mesa Source did for its HUD :
It's some sort of scanline filter, but instead of making some lines darker, it actually makes them more transparent.
Here's a test gif to show how it looks like on the player (even though I won't use it like that) :
It will be used on texts for the HUD/UI, and after testing it on bullet trails, I think it looks cool and I'm going to use it on them (the effect in the gif is a little bit too strong though).