smoke

smoke — Soft Particle Smoke Plume

Smoke is the same particle pattern as fire — billboard quads emitted from a small disc, drifting upward — except the shader is dim, soft, low-emission, and tinted by depth instead of glowing. Slower spawn rate, longer lifetime, larger end scale. Pair it with fire for any campfire/torch/explosion. Used everywhere: chimney smoke, smoldering wreckage, smoke trails behind rockets, steam from vents, fog clouds.

When to use

• "Smoke rising from the campfire."
• "Chimney smoke on the cottage."
• "Smoke trail behind the rocket."
• "Steam from the vent."
• "Smoke from the smoldering wreckage."
• "Fog cloud at the cave entrance."
• After spawning fire, smoke almost always belongs above it.

When NOT to use

• The user wants flames, not smoke — use fire.
• The user wants a giant ground-hugging fog volume — use a FogVolume node with the WorldEnvironment.volumetric_fog shader, not a particle system. Particles don't scale to room-size fog.
• The user wants a 2D smoke effect — canvas_item shader, not this.
• The user wants the smoke to physically interact with the player (pushed by movement) — particles are visual; use a FogVolume + script that follows the player.
• The user wants thick black bonfire smoke that completely occludes — bump density way up, but consider a FogVolume for genuine visual occlusion.

Recipe

1. Files to create

addons/vfx/_building-blocks/noise-3d-fbm.gdshaderinc   # copy from this skill FIRST
addons/vfx/smoke/smoke.gdshader
addons/vfx/smoke/smoke_controller.gd
addons/vfx/smoke/smoke.tscn

smoke.gdshader #includes the FBM noise file. A missing include is a hard compile error, so copy _building-blocks/noise-3d-fbm.gdshaderinc from this skill into res://addons/vfx/_building-blocks/ before writing the shader.

2. Shader code

addons/vfx/smoke/smoke.gdshader:

shader_type spatial;
render_mode unshaded, blend_mix, depth_draw_never, cull_disabled, shadows_disabled;

#include "res://addons/vfx/_building-blocks/noise-3d-fbm.gdshaderinc"

uniform vec4  smoke_color_young : source_color = vec4(0.85, 0.85, 0.85, 1.0);  // freshly emitted
uniform vec4  smoke_color_old   : source_color = vec4(0.45, 0.45, 0.45, 1.0);  // late life
uniform float density           : hint_range(0.0, 1.0) = 0.55;
uniform float noise_scale       : hint_range(0.5, 8.0) = 2.0;
uniform float noise_speed       : hint_range(0.0, 2.0) = 0.5;
uniform float soft_edge         : hint_range(0.01, 0.5) = 0.30;
uniform float depth_fade        : hint_range(0.0, 4.0) = 1.0;  // soft against geometry behind

// INSTANCE_CUSTOM is vertex-stage only, so carry what fragment() needs across.
varying float age;
varying float seed;

void vertex() {
    // Billboard toward the camera, keeping per-particle rotation (INSTANCE_CUSTOM.x)
    // and per-particle scale. The bare `VIEW_MATRIX * mat4(INV_VIEW_MATRIX[0..2],
    // MODEL_MATRIX[3])` form throws both away — this mirrors what Godot's own
    // BILLBOARD_PARTICLES generator emits (scene/resources/material.cpp:1313-1334).
    mat4 mat_world = mat4(
        normalize(INV_VIEW_MATRIX[0]),
        normalize(INV_VIEW_MATRIX[1]),
        normalize(INV_VIEW_MATRIX[2]),
        MODEL_MATRIX[3]);
    mat_world = mat_world * mat4(
        vec4(cos(INSTANCE_CUSTOM.x), -sin(INSTANCE_CUSTOM.x), 0.0, 0.0),
        vec4(sin(INSTANCE_CUSTOM.x),  cos(INSTANCE_CUSTOM.x), 0.0, 0.0),
        vec4(0.0, 0.0, 1.0, 0.0),
        vec4(0.0, 0.0, 0.0, 1.0));
    MODELVIEW_MATRIX = VIEW_MATRIX * mat_world * mat4(
        vec4(length(MODEL_MATRIX[0].xyz), 0.0, 0.0, 0.0),
        vec4(0.0, length(MODEL_MATRIX[1].xyz), 0.0, 0.0),
        vec4(0.0, 0.0, length(MODEL_MATRIX[2].xyz), 0.0),
        vec4(0.0, 0.0, 0.0, 1.0));
    MODELVIEW_NORMAL_MATRIX = mat3(MODELVIEW_MATRIX);

    // CUSTOM.x is the rotation angle, NOT the age. The age lives in CUSTOM.y
    // (it counts up by DELTA/LIFETIME) and CUSTOM.w holds the lifetime scale.
    age  = clamp(INSTANCE_CUSTOM.y / max(INSTANCE_CUSTOM.w, 0.0001), 0.0, 1.0);
    seed = fract(sin(float(INSTANCE_ID) * 12.9898) * 43758.5453);
}

void fragment() {
    // Distort UVs with slow noise.
    vec3 np = vec3(UV * noise_scale, TIME * noise_speed + seed * 10.0);
    float n = fbm3(np);

    // Soft round mask, modulated by noise so the silhouette is wispy not circular.
    vec2 c = UV - vec2(0.5);
    float r = length(c) * 2.0;
    float mask = smoothstep(1.0, 1.0 - soft_edge, r);
    mask *= (0.6 + 0.4 * n);  // bite chunks out of the puff

    // Fade in fast, fade out slow.
    float alpha_age = smoothstep(0.0, 0.15, age) * (1.0 - smoothstep(0.6, 1.0, age));

    // Color drifts young → old as it ages (cools off / dilutes).
    vec3 col = mix(smoke_color_young.rgb, smoke_color_old.rgb, age);

    ALBEDO = col;
    ALPHA = mask * alpha_age * density;
}