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The Fog and Volumetrics page
By Ryleigh Newman · Published
The Fog & Volumetrics page in Rockstar Shaders holds six settings: Fog steps, Fog range, Fog density, Horizon fade, Horizon fade width and Underwater shafts. The first three control one volumetric march that produces the fog and the light shafts, out to 224 blocks in 32 samples by default. The next two are the fade at the edge of the loaded world, and the last is the god rays under water.
I made Rockstar Shaders, a shader mod for Minecraft Java 26.3 on Apple Silicon Macs, and these help pages exist so every slider has a plain explanation beside it, written from the code as it stands in 1.0.
Download free (1.0.0) Modrinth (pending)Minecraft 26.3, Fabric, macOS on Apple silicon. Install guide. Releases and bug reports on GitHub.
What the volumetric march does
The fog in Rockstar Shaders is not a color ramp over distance. The air in front of the camera is divided into froxels, small cells laid out along the view, and the pack marches through them each frame to work out how much light each cell scatters toward you; one march produces the fog and the light shafts together. It reaches as far as Fog range and takes Fog steps samples to get there.
Two things feed each cell. The sky and sun visibility of every froxel is traced by the Metal side-car when Ray-traced fog is on, so a cell inside a cave knows it cannot see the sky. And colored block light reaches the fog through the block-light volume, so a lantern lights the air around it; that volume's known limit is that its light leaks through thin walls.
Fog steps and Fog range
Fog steps is the number of march steps for the light shafts and fog. The default is 32; the slider runs from 8 to 48 in steps of 4. Fog range is how far the march reaches, in blocks: 224 by default, from 48 to 320 in steps of 16.
The two go together: fewer steps over the same range means longer samples and coarser shafts, so if you want the fog cheaper, lower both. The pairings the code carries below the shipped 32 and 224 are 24 steps with 160 blocks, 16 with 128 and 12 with 96; there is no quality chooser on screen.
On the one machine measured, an Apple M4 Max with 48 GB, the volumetrics pass took 1.6 ms of a 46 ms frame at 1706x1966, looking down at the water in a sunset bay; the water pass was 8.7 to 8.9 ms, so the fog is not where the frame goes. Show pass timings on Performance and Overlays prints the live number for your own scene.
Fog density
Fog density is the overall density of the air. The default is 0.10; the slider runs from 0 to 0.5 in steps of 0.01. Raising it thickens the haze between you and a far hill; lowering it thins the air.
It does not change how far the fog reaches; that is Fog range. It is the slider to try first if the world reads as too clear or too hazy at every distance. In the Nether and the End the air has its own fog and ambient, on the Dimensions page.
Horizon fade and Horizon fade width
The original game dissolves the edge of the loaded world into the sky with fog. Horizon fade does the same and is on by default. Off shows the render-distance ring: the terrain ends where the chunks end.
Horizon fade width is how much of the render distance the fade spans, as a fraction. The default 0.10 is the original game's; the slider runs from 0.02 to 0.30 in steps of 0.01. A wider fade starts dissolving terrain closer to you.
With Extended horizon on, which it is by default, far terrain reaches 64 chunks, 1,024 blocks, and the fog treats it as geometry. The dithered join between vanilla's terrain and the far terrain belongs to View Distance, not to this page.
Underwater shafts
Underwater shafts sets the strength of the god rays under the surface. The default is 3; the slider runs from 0 to 6 in steps of 0.25.
These rays are separate from the fog above the water. The water engine draws the view from below with its own terms: Snell's window, the circle of sky you can see from under the surface; a water column tinted by the biome; caustics on the bed; and these shafts of sunlight. The Water page covers that engine; the three fog sliders above are the march in the air, not under it.
Ray-traced fog, and the fog without it
The switch that decides whether the side-car traces the fog's visibility is not on this page. Ray-traced fog is on Lighting and Shadows, on by default, and it is a restart setting.
Without the trace, the froxels do not know which of them are under a roof, and enclosed spaces look veiled: a cave or a house fills with the haze the open air has. The same happens where the Metal side-car cannot start. The log says why, in a line beginning "Ray tracing unavailable:" or "Ray-traced fog visibility disabled:", and Troubleshooting lists the reasons.
Turning the trace off does not buy speed. In one pose on the M4 Max, everything on was 27.9 ms a frame; Ray-traced fog off was 29.3 ms. The fallback costs more than the trace it replaces.
How a change applies, and what to look at next
Every setting on this page is a tune setting: it is stored as an override in config/rockstarshaders.json and applied when the page closes with Done, which rebuilds the shader pipelines in about a second and restarts the water's ripple field from flat. A value set back to the shader default is stored as no override, and Reset to defaults on the front page forgets every override.
To judge a change, See-through on the front page fades the menu so the world shows through it, and holding F1 on any Rockstar Shaders page hides the menu completely. The sky the fog sits under is on Sky and Clouds, and the block light that colors it is on Lighting and Shadows.
Download free (1.0.0) Modrinth (pending)Minecraft 26.3, Fabric, macOS on Apple silicon. Install guide. Releases and bug reports on GitHub.
Related
Questions
Why do caves and rooms look misty in Rockstar Shaders?
The fog's sky and sun visibility comes from the Metal side-car when Ray-traced fog is on. If that trace is off, or the side-car could not start, enclosed spaces look veiled. Ray-traced fog is on the Lighting and Shadows page and needs a restart; a missing side-car is explained in the log in a line starting "Ray tracing unavailable:".
How do I make the fog thinner or thicker?
Fog density. The default is 0.10 and the slider runs from 0 to 0.5. Fog range sets how far the march reaches, 224 blocks by default, and Fog steps how many samples it takes, 32 by default.
Does the volumetric fog cost a lot of frame time?
Not on the machine measured. At 1706x1966 on an Apple M4 Max with 48 GB, looking down at the water in a sunset bay, the volumetrics pass was 1.6 ms of a 46 ms frame; the water pass was 8.7 to 8.9 ms. Show pass timings gives you the number for your own scene.
Is it faster with Ray-traced fog off?
No. In one pose on the M4 Max, everything on was 27.9 ms a frame and Ray-traced fog off was 29.3 ms. The fallback costs more than the trace.
How do I see the edge of the render distance instead of the fade?
Horizon fade off shows the render-distance ring. Horizon fade width, 0.10 by default, is how much of the render distance the fade spans when it is on.
Does the fog look the same in the Nether and the End?
No. Each renders with its own sky, fog and ambient. The Overworld is the tuned target, and the record for the other two dimensions is three captures, so expect rough edges there.