Slipstream Viewer

An experimental third-party viewer for Second Life, built around a new GPU-driven Vulkan renderer. It started as a fork of Alchemy Viewer, itself built on Linden Lab's viewer, and has since diverged a long way: the render pipeline has been rewritten, and features from other viewers (plus some of our own) are being folded in.

Status: early and experimental. Linux x86_64 and Windows x64 test builds. Expect bugs, and please report them on the issue tracker.

Why

Second Life viewers traditionally render the way they did in 2007: the CPU walks the scene every frame, binds state and issues draw calls one face at a time. In busy places (clubs, crowds, mainland) the CPU becomes the bottleneck long before the GPU does. This viewer moves that work onto the GPU.

On an RTX 5090, a busy scene that runs around 24 FPS in a conventional GL-based viewer runs around 90 FPS here; quieter scenes hit the monitor's refresh rate. Numbers vary a lot by scene and hardware; these are indicative, not a benchmark.

The render engine

The Vulkan renderer owns the scene on the GPU. The CPU's per-frame job shrinks to streaming changes and dispatching a handful of compute and indirect draws.

• Persistent GPU scene. Every visible face lives in a persistent instance buffer (transform, material, bounds, flags) and a shared mega vertex/index buffer. Objects are uploaded when they change, not every frame.
• Bindless materials and textures. One large descriptor table holds every resident texture, and materials index into it. There are no per-draw binds.
• Compute culling + multi-draw indirect. A compute pass does frustum culling, LOD selection and bucket sorting (opaque, alpha-mask, alpha-blend, rigged, …) and writes indirect draw commands. The whole world draws in a few vkCmdDrawIndexedIndirectCount calls.
• Depth pre-pass. A depth-only pass over the same indirect draws, then the lit pass with depth-equal and early fragment tests, so every pixel is shaded exactly once (measured overdraw 2.7× → 1.0×).
• Clustered local lighting. Point lights and projectors are culled into screen-space clusters, so each pixel only evaluates the lights that reach it.
• GPU skinning and animation. Skin palettes (and animation evaluation) are computed on the GPU, with a pre-skin compute pass feeding the rigged draws. Crowds of avatars no longer eat the CPU.
• Streaming that follows visibility. Texture residency and quality follow what the GPU culler actually sees, with async uploads, a staging ring and a VRAM budget. Mesh decoding runs on worker threads.
• Modern post-processing. HDR, tonemapping, glow, SSR, reflection probes, and SMAA / FXAA anti-aliasing.

The legacy OpenGL pipeline is retired in this fork.

Features you won't find in other viewers

• Hardware ray tracing (RTX / RDNA2+). A ray-tracing foundation (BLAS per mesh LOD, a GPU-built TLAS, refit rigged avatars) with ray-traced projector shadows as the first consumer. They're exact, don't leak through walls, and keep up with moving stage lights. With the depth pre-pass they're often cheaper than shadow maps. Enable with RenderVKProjectorShadows = 2.
• Projector (spot light) shadows done properly. A shadow-map path with a much larger budget than usual, correct near-plane handling, and caching for static lights.
• Planar mirrors with occlusion-query gating: a mirror you can't see costs nothing.
• Third-person shooter camera (View → Third-Person Shooter Camera). The mouse steers the camera around your avatar, WASD moves relative to the camera, and left-click fires like mouselook. Right-click or Esc releases.
• Alchemy-style chat bar with optional nearby-chat toasts alongside chat bubbles.
• Correct rendering of huge sim-surround objects (weather domes and the like), which are far-clipped away in some renderers.

Requirements

• Linux x86_64, glibc ≥ 2.38, a CPU supporting x86-64-v2.
• A GPU with a Vulkan 1.3 driver (NVIDIA proprietary, or Mesa RADV for AMD).
• Ray-traced features need VK_KHR_ray_query: NVIDIA RTX 20-series or newer, AMD RX 6000 or newer. Without it, everything else still works and ray tracing switches off automatically.

Download

Test builds are published as releases. Each release lists a SHA-256 checksum. Linux: unpack the tarball and run ./slipstream from the extracted folder. Windows: unzip and run SlipstreamViewer.exe.

Building (Linux)

The repo includes a Makefile that wraps the autobuild/CMake flow:

make            # venv + deps + configure + build + package
make run        # launch the packaged viewer
make clean      # drop the build dir, keep caches

Run make help for targets and overrides (configuration, extra CMake flags). The first build downloads about 1 GB of prebuilt third-party libraries.

Useful settings

Setting	What it does
RenderVKProjectorShadows	0 off, 1 shadow maps, 2 ray traced
RenderVKRayTracing	0 off, 1 auto (ray tracing when supported)
RenderVKDepthPrepass	Depth pre-pass on or off (default on)
RenderVKGpuTimers	Log per-pass GPU timings (for performance reports)
AlchemyTPSCamera	Third-person shooter camera

Credits and license

Built on the work of Alchemy Viewer and Linden Lab's Second Life viewer, and includes RLVa. Source is licensed under the LGPL 2.1; see doc/LICENSE-source.txt and doc/LGPL-license.txt. Second Life and related marks belong to Linden Research, Inc. This project is not affiliated with or endorsed by Linden Lab or the Alchemy Viewer team.