Screenshot 1 of 5. Alpha Piscium shader rendering path-traced global illumination inside St. Peter's Basilica in Minecraft
What Alpha Piscium works with.
| Platform | Java Edition |
|---|---|
| Loaders | Iris |
| Minecraft versions | 1.20.5, 1.21.1, 1.21.11, 26.1, 26.2 |
Alpha Piscium is a realistic Iris shader pack for Minecraft Java built around path-traced style global illumination rather than the flat baked lighting most shader packs use. It reaches Minecraft 26.2 in beta, with a build published on September 9, 2026, so it is actively maintained rather than stalled on an old version.
What Alpha Piscium changes in Minecraft
The pack replaces vanilla and OptiFine-style lighting with a screen-space global illumination pipeline called ReSTIR SSGI, cleaned up with a ReBLUR denoiser so the indirect lighting does not look noisy or grainy. A specular GI pass adds reflective indirect light on top of the diffuse bounce lighting, so metallic and wet surfaces pick up believable reflected color instead of flat shading.
- Adaptive RTWSM shadow mapping with rectilinear warping for sharper, more efficient shadows at a distance
- A custom sky renderer with epipolar sampling for atmospheric scattering and light shafts
- Volumetric, shapeable clouds rendered in real time rather than a flat cloud plane
- Water and glass rendering with surface reflection, refraction, and optical depth
How to install Alpha Piscium with Iris
- 1.Install Fabric or Quilt with Iris 1.7 or newer, since Alpha Piscium only runs on the Iris shader loader.
- 2.Download the shader pack zip from Modrinth without unzipping it.
- 3.Open the Minecraft shaderpacks folder from the Iris menu and drop the zip file in.
- 4.Select Alpha Piscium from the Iris shader list and apply it.
The pack has no required Modrinth dependencies beyond Iris itself, so there is no separate API or library mod to track.
Hardware requirements and performance
Path-traced global illumination is heavy by design, and Alpha Piscium is upfront about hardware limits: it needs AMD driver version 22.7.1 or newer, is optimized for NVIDIA hardware, and does not support Intel GPUs at all. Integrated graphics and older dedicated cards should expect this to be unplayable rather than just slow, since the effect stack is built for a modern discrete GPU, not scaled down for low-end hardware.
A full path-traced pipeline is not the only way to get realistic lighting. A semi-realistic pack like Complementary Unbound or the voxel-based global illumination in Rethinking Voxels targets a wider range of hardware for readers whose GPU cannot run Alpha Piscium.
Supported Minecraft versions
Alpha Piscium supports Minecraft Java from 1.20.5 through the 26.2 release, all on the single Iris loader. The project ships frequent beta builds rather than infrequent stable releases, and the version_type on most builds is beta, which reflects how fast the shader's rendering techniques change rather than a sign the pack is unfinished.
Known issues
Because the global illumination is screen-space, lighting can go dark or lose detail when the camera looks somewhere the previous frame never rendered, most noticeably when spinning the camera to face backward quickly. This is a structural limit of screen-space techniques rather than a bug that will be patched out.
Frequently asked questions
Alpha Piscium shader review and gameplay test
Questions about Alpha Piscium.
5 questions
How do I install Alpha Piscium?
Install Iris 1.7 or newer on Fabric or Quilt, download the shader pack zip from Modrinth, and drop the unopened zip into the shaderpacks folder from the Iris menu. Then select Alpha Piscium from the in-game shader list. No other mods or dependencies are required.
Does Alpha Piscium work with OptiFine?
No. Alpha Piscium only supports the Iris shader loader, not OptiFine. Iris runs on Fabric and Quilt, so players need one of those mod loaders plus Iris installed before the shader pack will show up in the shader menu.
Which Minecraft version does Alpha Piscium support?
Alpha Piscium currently reaches Minecraft 26.2, with builds also covering versions back to 1.20.5. New beta builds ship regularly, with the latest published on September 9, 2026, so the version range keeps extending as new Minecraft drops release.
Is Alpha Piscium good for low-end PCs?
No. It is a path-traced shader with a heavy effect stack, needs a modern AMD or NVIDIA GPU, and does not run on Intel graphics at all. Players on integrated graphics or older dedicated cards should look at a lighter semi-realistic pack instead.
Where can I download Alpha Piscium?
Alpha Piscium is distributed through its official Modrinth project page. It is released under the GPL-3.0-only license, with source code public on the creator's GitHub repository, so its build process and permissions are verifiable rather than opaque.
