fog_modifier¶

type: "fog_modifier"

Changes the vanilla fog — how near or far it starts and ends, and optionally its colour. It is a value modifier at the source of the fog, not a screen post pass: the mod rewrites the fog distances and colour at the return of vanilla FogRenderer.setupFog, mutating the instance the game produced, before anything consumes it. The same values then reach the fog uniforms (FogEnvironmentalStart/End, FogRenderDistanceStart/End, FogSkyEnd, FogCloudsEnd, FogColor), the level renderer and the sky/cloud shaders, so vanilla terrain, entities, the horizon band and the mod's own world/entity geometry all see the modified fog.

Iris: under an Iris shaderpack this effect is a no-op. A pack computes its own fog and ignores the vanilla fog values, so there is nothing for the modifier to change. This is inherent to modifying vanilla fog at its source; it is not a bug.

Fields¶

Camera and value effects also accept the shared definition fields (duration, easing, loop, persistent, fade_ticks, sound).

Field	Type	Default	Meaning
`fog_start_scale`	float	1.0	Multiplier on the fog start distance. `1.0` = vanilla, `>1` = fog starts further (see further), `<1` = fog starts closer
`fog_end_scale`	float	1.0	Multiplier on the fog end distance (where the fog is fully opaque). Same meaning as above
`fog_r`	float	unset	Optional red channel of a fog colour override, `0..1`
`fog_g`	float	unset	Optional green channel of a fog colour override, `0..1`
`fog_b`	float	unset	Optional blue channel of a fog colour override, `0..1`
`fog_color_amount`	float	unset	How far the colour moves from vanilla: `0` = vanilla colour (not touched), `1` = the full authored colour, in between blends. Unset = `1`

All six are ordinary animatable params: start/end, keyframes, expr, graphs, setParam and bind all work, and fade_ticks fades the effect in and out by its weight. The colour params are optional: a channel that is not authored (fog_r absent) leaves the vanilla colour for that channel unchanged, and when none of the three is authored the vanilla colour is used bit-for-bit.

Smooth colour transition. The colour params are all-or-nothing at the effect's own weight — the only thing that moved the colour was the fade. fog_color_amount decouples that: author a constant colour and keyframe fog_color_amount from 0 to 1 to ramp smoothly from the dimension's vanilla fog colour to the authored one (and back). 0 is a true no-op — the colour is not even written — so an unauthored fog_color_amount keeps today's behaviour exactly.

How effects combine¶

Several fog_modifier effects can overlap. They combine the same way no matter which order they run in:

Scales are additive around neutral. Each effect contributes (scale − 1) × weight, so the combined scale is 1 + Σ((scale − 1) × weight). Two effects that each pull the fog to 2× give 3×, not 4×; an effect at 1.0 adds nothing.
Colour is averaged, not applied in sequence. The authored colours are averaged weighted by each effect's weight (scaled by its fog_color_amount), then the vanilla colour is blended toward that average by the clamped total weight (per channel, clamped to 0..1). Because the average is a sum, the result does not depend on the iteration order. An effect with fog_color_amount 0 contributes no colour at all and its colour channels are never written; an unauthored amount counts as 1.
An effect whose weight is 0 (faded out) contributes nothing.

The scales are applied to both the environmental fog range and the render-distance fog range, which is what makes them visible in normal play (the shader's fog amount is the stronger of the two).

What is and is not covered¶

Covered: every distance-based fog on 26.2 / 26.1.2 / 1.21.11 — the atmospheric fog of the overworld, the nether (fog_start_distance 10 / fog_end_distance 96) and the End (both use the same FOG_START_DISTANCE/FOG_END_DISTANCE environment attributes), plus water, lava, powder-snow and blindness/darkness fog. They all end up in the same four FogData distance fields, which is the single point the modifier rewrites.
Not covered (verified absent): there is no density-based fog on these versions. FogData has no density field and EnvironmentAttributes has no density attribute on any of the three nodes, and the dimension definitions express fog as start/end distances. The distance scales are therefore the complete control.
Sky and cloud fade (FogSkyEnd, FogCloudsEnd) scale with fog_end_scale like the distance ends, so fog_end_scale < 1 narrows the horizon band and brings the clouds in. They have no start value, so fog_start_scale never affects them.
The zenith keeps the dimension's own sky colour. The sky shader fogs ColorModulator toward the fog colour and only the far horizon actually reaches it, so an authored fog colour tints the horizon band and the clouds but not the top of the sky. That contrast is vanilla behaviour, not a bug.
The mod's own world/entity geometry: the entity effect pipelines (entity_tint, entity_outline, entity_displace) read the same fog uniforms, so they inherit the change. The block_tint/block_outline/glow/spark overlays use the core/position_color shader, which does not sample fog at all, so they are unaffected either way.

Example¶

{
    "type": "fog_modifier",
    "duration": 80,
    "fade_ticks": 10,
    "params": {
        "fog_start_scale": { "start": 0.35, "end": 1.0 },
        "fog_end_scale": { "start": 0.5, "end": 1.0 }
    }
}

Pull the fog in for a claustrophobic beat (both ranges at ~40%), then let it return to vanilla. A colour override is three extra params:

{
    "type": "fog_modifier",
    "duration": 120,
    "params": { "fog_r": 0.1, "fog_g": 0.3, "fog_b": 0.25 }
}

Ramp that colour in smoothly by animating fog_color_amount while the colour stays constant — the fog starts on the dimension's own colour and blends to the green mist over five seconds:

{
    "type": "fog_modifier",
    "duration": 100,
    "params": {
        "fog_r": 0.1,
        "fog_g": 0.3,
        "fog_b": 0.25,
        "fog_color_amount": { "start": 0.0, "end": 1.0 }
    }
}

/vfx play vfxweaver:fog_modifier {[fog_start_scale:0.4,fog_end_scale:0.5]}

Code¶

/vfx play vfx_demos:show_fog_modifier

Its datapack definition (the fog closes in, opens up past vanilla and returns, while a green tint ramps from vanilla at the midpoint and back to vanilla at the loop ends):

{
    "type": "fog_modifier",
    "duration": 240,
    "easing": "ease_in_out_cubic",
    "persistent": true,
    "loop": true,
    "fade_ticks": 12,
    "params": {
        "fog_start_scale": {
            "keyframes": [
                { "time": 0, "value": 1.0 },
                { "time": 60, "value": 0.4 },
                { "time": 120, "value": 1.0 },
                { "time": 180, "value": 2.0 },
                { "time": 240, "value": 1.0 }
            ]
        },
        "fog_end_scale": {
            "keyframes": [
                { "time": 0, "value": 1.0 },
                { "time": 60, "value": 0.4 },
                { "time": 120, "value": 1.0 },
                { "time": 180, "value": 2.0 },
                { "time": 240, "value": 1.0 }
            ]
        },
        "fog_r": 0.15,
        "fog_g": 0.35,
        "fog_b": 0.3,
        "fog_color_amount": {
            "keyframes": [
                { "time": 0, "value": 0.0 },
                { "time": 60, "value": 0.5 },
                { "time": 120, "value": 1.0 },
                { "time": 180, "value": 0.5 },
                { "time": 240, "value": 0.0 }
            ]
        }
    }
}

Code¶

/vfx play vfx_demos:show_fog_modifier

Its datapack definition:

{
    "type": "fog_modifier",
    "duration": 240,
    "easing": "ease_in_out_cubic",
    "persistent": true,
    "loop": true,
    "fade_ticks": 12,
    "params": {
        "fog_start_scale": {
            "keyframes": [
                {
                    "time": 0,
                    "value": 1.0
                },
                {
                    "time": 60,
                    "value": 0.4
                },
                {
                    "time": 120,
                    "value": 1.0
                },
                {
                    "time": 180,
                    "value": 2.0
                },
                {
                    "time": 240,
                    "value": 1.0
                }
            ]
        },
        "fog_end_scale": {
            "keyframes": [
                {
                    "time": 0,
                    "value": 1.0
                },
                {
                    "time": 60,
                    "value": 0.4
                },
                {
                    "time": 120,
                    "value": 1.0
                },
                {
                    "time": 180,
                    "value": 2.0
                },
                {
                    "time": 240,
                    "value": 1.0
                }
            ]
        },
        "fog_r": 0.15,
        "fog_g": 0.35,
        "fog_b": 0.3,
        "fog_color_amount": {
            "keyframes": [
                {
                    "time": 0,
                    "value": 0.0
                },
                {
                    "time": 60,
                    "value": 0.5
                },
                {
                    "time": 120,
                    "value": 1.0
                },
                {
                    "time": 180,
                    "value": 0.5
                },
                {
                    "time": 240,
                    "value": 0.0
                }
            ]
        }
    }
}