ZDoom

Due to a bug in its handling of certain types of graphics cards and DirectX versions, Doom95 does not render the partial invisibility effect in its original form. Instead of seeing directly through the sprite, with some cards the user sees a wall texture or other background "refracted" through the creature's body at a slight angle, as though looking at an object through a glass of water. This makes invisible enemies somewhat easier to see, especially in dark rooms; on the other hand, tracking the movement of non-invisible creatures behind them can be more challenging, especially when trying to aim one's weapon through a pile of invisible corpses (which can easily occur, for example, in E1M9: Military Base). On other cards the effect produces bright yellow and magenta pixels which make the affected things stand out very clearly. Both visual glitches can be prevented by disabling DirectDraw acceleration using the -emulate parameter.

Nash wrote:GZDoom has one fuzzy rendering mode (via OpenGL shaders) that makes the size of the pixelated fuzziness equivilent to a 320x200 screen, regardless of the user's video mode.