A "Citra shader" refers to a custom user-created or pre-installed graphical filter used within , an open-source emulator for the Nintendo 3DS. Dhamakamusicin - 3.79.94.248
These shaders are small pieces of code that alter the visual output of the emulator. They are used to simulate the look of old CRT televisions, smooth out pixelated graphics, or apply artistic effects. Super Smash Bros Ultimate Switch Nsp Mise A Link - 3.79.94.248
Here is a detailed write-up on the technical aspects, usage, and popular types of shaders in Citra. The Nintendo 3DS has a native screen resolution of $400 \times 240$ (top screen) and $320 \times 240$ (bottom screen). When upscaled to a modern 1080p or 4K monitor, the image can look blocky or "jagged" due to nearest-neighbor scaling.