Mode 13h: MS-DOSify!

An Iris shader pack for Minecraft that recreates the look of late-90s MS-DOS 3D graphics with deliberate retro accuracy.

Mode 13h: MS-DOSify! is not just a generic “pixelation” shader. It aims to reproduce the actual visual limitations and quirks that gave old DOS-era 3D games their unmistakable look: low resolution, wobbly software texture mapping, a fixed 256-color palette, colormap lighting, billboarded sprites, and carefully tuned fog.

It supports Minecraft 1.20.1 and 1.21.1 with Iris or Oculus; every release is tested on both. Newer versions are best-effort.

Recommended render resolution: 1280 x 800
The shader pack is designed to downscale by 4x to an internal 320 x 200 image, matching classic Mode 13h output.
For the most authentic look, stretch the final image to 4:3 to reproduce the era’s non-square pixels.

🧾 Why This Exists

A lot of “retro” shaders stop at chunky pixels and call it a day.

Mode 13h goes further. It tries to recreate the specific rendering artifacts that defined old DOS-era 3D, including the quirks modern graphics usually try to hide or eliminate. The goal is not just to look old — it is to feel like an actual late-90s PC pushing textured 3D slightly beyond its comfort zone.

✨ Features

📺 Authentic low-resolution output

• The image is downscaled to a Mode 13h-style 320 x 200 internal resolution.
• This gives the shader pack the crunchy image structure typical of classic DOS graphics.
• Textures pick their mipmaps for that 320 x 200 image, so distant surfaces don't shimmer.

🧱 Quake-style texture mapping

• Like Quake, textures are perspective-correct only every 16 pixels and linear in between, giving the subtle texture wobble of software-rendered 3D.
• Want the full PlayStation-style warping? Switch to affine mapping. Prefer it clean? Perspective-correct is there too.

🎨 A real 256-color palette

• Every pixel is drawn from a fixed 256-color palette, like a DOS game's own.
• The default ramp palette has 16 Minecraft hues (stone, dirt, grass, water, lava, gold…) in 16 shades each.
• Prefer the classic? Pick the stock VGA palette, or the computed RGB332 and 6 x 6 x 6 palettes.
• Or play in the colors of a classic: Wolfenstein 3D, Doom, Heretic, Hexen, Quake, Duke Nukem 3D, Daggerfall, or the Mac OS system palette.

💡 Colormap lighting

• Textures only use palette colors, and shadows step down each color's ramp instead of dimming smoothly — just like the colormaps of Doom and Quake.
• Light is quantized into configurable brightness steps; 16 matches vanilla Minecraft’s light levels.

🌫️ Tuned fog

• Fog keeps vanilla's shapes and curves but starts at half the vanilla distance by default, selling depth the way older games did.
• Start, End and Density scales in the menu let you push it thicker or back to vanilla.

🪧 Billboarded sprites

• Flowers and grass, torches, lanterns, chains, amethyst, bamboo and hanging propagules render as 2D billboards that always face the player.
• This mimics the sprite-based tricks commonly used in older 3D games.
• Signs and more blocks can billboard too, with the add-ons below.

✋ Painted viewmodel

• First-person hands and held items are drawn flat and unlit, like the painted weapon sprites of old shooters.
• An ordered dither at 320 x 200 scale breaks up their gradients before the palette.

💧 Night water

• Water turns darker and more opaque in low light, so rivers and oceans read as black depths at night.

⚙️ Configuration

The shader includes a configuration menu with several options so you can fine-tune the effect to your taste.

You can adjust things such as:

• Pixel scale (resolution reduction)
• Palette: ramp, stock VGA, RGB332, 6 x 6 x 6, Mac OS, seven classic game palettes, or off
• Colormap lighting, light steps and ambient floor
• Texture mapping: subdivided, affine or perspective-correct, and the span width
• Fog start, end and density
• Hands: flat sprite look and dithering strength
• Add-on compatibility toggles, which can be enabled or disabled individually

🔧 Technical Notes

• Requires Iris or Oculus. OptiFine is not supported.
• Supported: Minecraft 1.20.1 and 1.21.1. Newer versions are best-effort.
• Targets OpenGL 4.1, so it can also run on macOS.
• Lightweight: a handful of geometry passes and one final pass, no composites.
• Upgrading from 1.x: settings for removed or renamed options reset to their defaults.

🧩 Add-ons

Mode 13h also has optional companion add-ons that expand the billboarding system.

Important: Add-ons are not included with the shader pack. They must be downloaded separately.

🪧 Flatter Signs

Flatter Signs is a mod that changes signs into cross/hatch models, allowing Mode 13h to billboard them like flowers or grass.

Without the shader pack, those signs simply render as flat cross/hatch objects. With Mode 13h enabled, they become proper DOS-style billboarded signs.

🧱 Billy Boarding (WIP)

Billy Boarding is a resource pack that changes the .json block models of selected blocks so they become cross/hatch-based and therefore compatible with the shader’s billboarding system.

If you install these add-ons, you can enable or disable their dedicated support from the shader configuration screen.

🌌 Recommended with a Stylized Sky

For the best overall presentation, it is recommended to pair Mode 13h with a stylized skybox.

At the moment, the recommended choice is Anime Sky.

A bespoke skybox made specifically for Mode 13h may come in the future.

❌ What It Is Not

• Not just a simple “pixelation” filter
• Not a generic CRT-style retro effect: it emulates the signal, not the monitor. No CRT curvature, scanlines or bloom; stretch to 4:3 yourself.
• Not a clean or modernized take on retro visuals

Mode 13h intentionally embraces visual instability, harsh quantization, and awkward old rendering tricks — because that is the whole point.

🖇️ Credits

• Shader pack & idea: HandLock_

🛠️ Development

See AGENTS.md.

“If the textures don’t wobble, it’s not old enough.”