Shaders are filters applied to the game image in real time: scanlines, CRT curvature, cel shading, smoothing… Recalbox ships a collection of them, but only in the .glslp format. Yet several cores, especially those of 3D consoles (Nintendo 64, PlayStation, Dreamcast…), only accept the .slangp format: in the RetroArch menu, Quick Menu → Shaders → Load Preset then shows an empty folder (No Items).
This page explains how to add the slang shader collection yourself.
The slang format works with the OpenGL graphics driver just as well as with Vulkan. What determines the usable format is the core, not the driver.
On a modern screen (Full HD or 4K), the step that genuinely improves the rendering of 3D consoles is not the shader but upscaling: having the game rendered at an internal resolution higher than the original one. Recalbox offers the HD mode for that, on machines powerful enough. The shader sits on top of it: it will not rescue a low-resolution image.
<> Code button → Download ZIP.slang-shaders-master folder.shaders_slang (the name is up to you, but keep it short and space-free).shaders folder of your Recalbox share, that is /recalbox/share/shaders/shaders_slang. The \\RECALBOX\share network share lets you do it straight from a computer — see File management./recalbox/share/shaders is exactly the folder RetroArch opens when you look for a preset: anything you drop there becomes selectable.
Recalbox forces its own shader onto the emulators whenever one is configured in its menus, which would override your choice. Before going further, leave both settings on NONE:
START → IN-GAME SETTINGS:
SHADERS SET: NONE;ADVANCED SHADERS: NONE.The
ADVANCED SHADERSmenu only lists.glslpfiles: the.slangppresets you just installed will not appear there. That is expected — they are loaded from RetroArch, as described below.
HOTKEY + B (see Special commands).Quick Menu → Shaders → Load Preset.shaders_slang, then into the category you want: crt, cel, deblur, handheld, scanlines…MMJ_Cel_Shader.slangp for instance): it is applied immediately.Without saving, the shader is lost when you quit the game. Still under Quick Menu → Shaders:
Save → Save Game Preset: the shader applies to this game only;Save → Save Core Preset: the shader applies to every game run with this core.Shaders are computationally expensive. On a modest machine a heavy preset can wreck the frame rate, or even freeze the emulator. Start with light presets (
crt/crt-pi,scanlines) before trying the elaborate ones. If everything locks up, quit withHOTKEY+STARTor reboot the machine.