Shader

A shader is a real-time image filter applied to emulated output, most famously CRT shaders that reproduce the scanlines and glow old games were designed to be seen through, or LCD-grid shaders for handheld systems. Beyond nostalgia, a good CRT shader can make pixel art look the way its artists intended. Shaders cost a little GPU power, so on a device near its ceiling they are one more thing competing for the frame budget — usually worth it below the ceiling, a luxury to drop at it.