Light the Trail: user manual

Trails from anything that moves: a sword, a car, a rocket, a hand, a whole character. Light streaks, solid mesh ribbons, light walls, ghost copies and real smoke, plus streaks that loop along a curve. Blender 4.5, 5.1 and 5.2, Cycles and EEVEE.

Install

Edit > Preferences > Get Extensions > the arrow menu at the top right > Install from Disk, and pick the zip. The panel is in the 3D Viewport sidebar (press N), on the Trails tab.

Quick start

1. Select the thing that moves. It has to be animated already: the trail follows its animation.
2. In the Trails tab, press Add Trail. It records the motion (usually well under a second) and draws the trail.
3. Play, or jump to any frame. The trail is right on every frame, even one you jump straight to.
4. Pick a Look, then set Length (how many frames of motion the trail shows) and Width.
5. Before you render, press Render Check at the bottom of the panel.

Or skip steps 2 to 4: select the thing and click one of the seventeen presets at the top of the panel.

Nothing moves, no trail. If what you selected does not move during the scene's frames, Add Trail adds nothing and tells you why. Animate it first.

What gets a trail

What you select decides what kind of trail you get. The line under the Add Trail button tells you what it will make before you press it.

A trail on a character's hand or foot: select a few vertices on the hand in Edit Mode, or the hand bone in Pose Mode, then Add Trail. Selecting the whole body gives ghosts, because a ribbon through the middle of a body does not look like anything.

How the trail follows the motion

Add Trail records the motion once, four times a frame (Samples; use 8 for very fast flicks), and keeps it inside the trail itself. So:

• any frame is right, even one you jump straight to, and a render farm renders it the same;
• the file renders the same on a computer that does not have the add-on;
• moving or parenting the trail object changes nothing. The trail stays where the motion was.

Change the animation and the trail records again by itself, a moment after you stop editing. A trail whose record takes longer than a second and a half waits for you instead: the panel says the animation changed, and Re-record does it. Auto Re-record turns this off for one trail.

If you make the scene longer after adding a trail, Render Check records it again over the new frames.

Shapes

• Ribbon: a flat strip. Facing sets which way it turns. Auto spans the blade when there are two recorded points (a sword, two objects, two vertices), and faces the camera otherwise. Camera always faces the camera. Flat lies level.
• Tube: round, the same from every side. Tube Sides sets how smooth it is.
• Wall: an upright strip standing on the path, like the light walls behind the bikes in Tron. Width is its height. Use Lift to move it up or down (the Tron preset sets it so the wall runs from the bottom of the bike to its top).
• Smoke: real smoke, a volume lit by your lights in both Cycles and EEVEE. It is made of puffs left behind as the thing moves. Each puff rises (Rise), churns about (Billow) and spreads (Taper below 0) as it ages, and old smoke breaks up and is gone by the end of Length. Width is how wide the smoke starts, and Puffs per Frame is how many puffs are left each frame (raise it if fast smoke looks lumpy). Switching to Smoke gives the trail a smoke material. Switching back gives its old look back.

Taper narrows the trail towards its tail. Below 0 it widens instead.

Detail is how many points the trail has per frame of motion, and Cross Rows (in the modifier's own settings) how many strips it has across its width. A trail on a blade (or a bone, or two points) starts at Detail 32 and 4 Cross Rows: a blade's hilt end moves much less than its tip, so with fewer, the stripes, bands and the core line of a look come out as stair-steps, and soft looks show rays, on a fast swing. A trail from one point starts at 8 and 1. Raise Detail if a very fast swing still looks faceted. The finer mesh costs 0.5-0.9 ms more a frame to play and at most 2 % more render time (measured on a sword swing, Cycles, 1280 x 720, 128 samples).

Speed gate

Speed Gate hides the trail where the motion is slow, so a sword only leaves a trail during the swing and not while it is held still. It is a share of the fastest the source moves: at 0.45 the trail shows where it moves at more than about half its top speed. 0 turns it off. Gate Softness fades the trail in and out gently around the gate, and Speed Width thins it as well as fading it.

Looks

Every trail gets its own copy of its look, so changing one trail's colours does not change another's.

Petals and Magic Sparkle are the last two in the menu. They give any trail what those presets give it: the look and its petals or stars. Your trail keeps its own length and width (the presets also make Petals' trail longer and Magic Sparkle's thin).

To try Anime Fire on a sword, add Fire Sword, then pick Anime Fire in Look: it keeps the embers and the flames on the blade, and sets Blade Drag, Cross Rows and a wider band on the blade (Blade Size 0.20) for itself (picking Fire again gives the trail its own values back). Its colours are flat and bright, so they look best in the Standard view (Render Properties > Color Management); under AgX, Blender's default, they come out a little duller, and Render Check says so.

What changes when you pick a look. A look brings its own particles and settings, and gives back what it changed when you pick another one, but it never undoes a change you made yourself:

• Its particles. Each look has the particles its preset uses: embers on Fire and Anime Fire, round blobs on Water, leaves on Wind, shards on Ice, sparks on Lightning, glints on Slash, flecks on Anime Ink, motes on Neon, and none on Light Streak and Smoke. Picking a look swaps the particles for its own, as long as they are still the ones the last look or preset gave the trail. If you changed any particle setting, picked a type yourself or set None, they are yours and stay as they are. Picking the look the trail already has gives it that look's particles back. Petals and Magic Sparkle are different: picking one always gives the trail its petals or stars, even if you changed the particles, because without them there is nothing to see. Leaving them works like any other look: another look swaps the petals or stars for its own particles, and picking Wind or Neon gives that look's leaves or motes. Change any of their settings first and they stay.
• Soot, Frost Mist and Ground Strikes. A look without its own extra takes the old one away (Fire's soot does not stay on Water, and lightning strikes stop when you pick Ice). The look never adds one: tick it yourself.
• Anime Fire sets its own Cross Rows and blade band (above), and gives the trail's own values back when you leave it.

The panel shows the main settings of the look. All of them are on the trail look node in the trail's material ("More in the trail's material"). Hover over any of them for what it does, or see the list at the end of this manual.

Light the Scene (Cycles only): the trail lights and reflects in what is around it, so a sword slash lights up the floor under it. Light Strength sets how much light it throws without changing how bright the trail itself looks. Off, the trail only glows. EEVEE does not light the scene from a trail, whatever this is set to.

Lightning strikes

With the Lightning look, tick Ground Strikes in the look's box (where Soot and Frost Mist go on Fire and Ice). It starts at 2 bolts a second. Untick it to stop them; tick it again and they come back at the rate you had. Lightning Trail and Lightning Slash tick it for you. Picking another look turns them off. Ticked, it shows:

• Strikes per Second: bolts that leap off the trail or the blade. Every other bolt hits the floor (or your target) with a flash where it lands; the rest fork out into the air. Most come while the sword swings fast, and a few still come while it is still. Each bolt lasts 4 frames and flickers with the trail. 0 turns them off and unticks the box.
• Reach: how far a bolt can go, in blade lengths. A bolt that cannot reach the floor forks into the air.
• Target: a collection of objects for the bolts to hit, like the floor and a few props. Empty, they hit the floor below the sword. Leave the character out of it, or bolts land in the hand that holds the sword.
• Strike Ground (in the modifier's own settings): the floor's height when there is no target. It is found when the trail is made, from the floor below the source; change it if your floor moved.

The bolts are worked out for each frame from the recorded motion, like the trail: nothing to bake, the same picture on any computer, and they render without the add-on. In Cycles, with Light the Scene on, each bolt lights the floor where it lands. EEVEE draws the bolts and the flash where they land, but does not light the floor.

Render time, measured on Remy's swing (Cycles, 1280 x 720): the bolts add at most about 2 % to a frame, so the strikes cost almost nothing to render. Playing the scene, the trail takes about 4 ms longer a frame to work out; a Target collection adds more, about 18 ms a frame for 100,000 faces, so keep the target to the floor and a few props. Render Check warns about a target over 200,000 faces, and about one that holds a trail.

Your own material: put any material in the trail's Material slot. The trail gives it these to read with an Attribute node: trail_age (0 at the head, 1 at the tail), trail_side (0 to 1 across), trail_gate (the speed gate), trail_frame (the frame that bit of trail was drawn) and the UVMap.

Particles

Particles sends particles flying out of the trail. They take the trail's own colours, so they always match.

• Sparks: fast and thin, falling, from the head.
• Embers: slow, rising and drifting, from along the trail.
• Flow: a soft drift off the whole trail.

Picking one fills in its settings, sized to the trail. Change any of them after.

• Emit From: Head (the tip) or Along (anywhere on the trail as it is drawn).
• Amount (born per frame), Particle Life (in frames), Particle Speed, Particle Drag (air slowing the fling, so they burst out and coast to a stop; 0 = none), Inherit (how much of the trail's own motion they carry), Gravity (below 0 they rise), Drift (wandering).
• Over their life: Shrink, Size Curve and Opacity Curve work the same as in Break It Any Way. Shrink 1 shrinks them to nothing, 0 keeps their size. Opacity Curve 0 never fades them.
• Shape: Points, Streaks (stretched along their motion), your own Object, or a Collection to pick from at random. Your objects take the trail's colours unless you tick Keep Own Material. Face Camera turns each one to face the camera and keeps it upright, so a flat shape (a star, a heart, a logo) always reads; Spin then turns it slowly in the picture. It costs no render time.
• Override Material gives them a material of your own instead.

The particles are worked out for each frame, like the trail, so there is nothing to bake.

Ghosts

Add Ghosts leaves fading copies of the selected object behind as it moves. On a character it copies every mesh the armature moves, and anything it carries, like a sword. Add Trail on a character's body or armature makes ghosts for you.

• Spacing: frames between ghosts. Changing it records again.
• Copies per Frame: ghosts recorded between frames, for smears on very fast moves (4 puts one every quarter of Spacing). Memory, file size and record time grow the same way: a 19,000-vertex character over 107 frames at 4 is about 100 MB.
• Life: how many frames a ghost stays. Delay: frames before a new ghost appears, so it does not sit on the body.
• Speed Gate: ghosts only where the character moves fast.
• Smear: copies keep only the parts that move fast and grow out of the body where it is now, like an animator's multiples (arms and a sword fanned from the shoulder). Parts slower than this share of the top speed stay on the body. 0 keeps whole copies.
• Limb Spacing and Limb Fade: copies of the character's own body (arms, hands, clothes) are spaced further apart (Limb Spacing, in frames) and turn see-through as they age (Limb Fade), while a sword or anything else it carries keeps every copy, solid. With Smear this keeps a few faint arms instead of a solid fan of them. Limb Fade needs Ghost Look off; it keeps faded copies of the body's materials, so Re-record after you change those. 0 turns each off.
• Ghost Look on: a see-through copy glowing at its edges. Off: the character's own materials.

A long animation on a heavy character takes memory; the panel says how much, and warns when it gets large.

Path streaks

Add Trail on a curve makes streaks that flow along it. They are drawn straight from the curve, so editing the curve updates them as you go.

• Streaks per spline, Streak Length (a share of the curve), Offset, Spread (0 spaces them evenly, 1 scatters them), Reverse.
• Loops, Loop Frames and Start: each streak goes round Loops times in Loop Frames. Loop Frames starts out as your scene's length, so the last frame flows into the first and the animation loops with no jump. If you change the scene's length, Render Check tells you what to set Loop Frames to.
• An open curve: the streaks come in at one end and leave at the other.
• Ribbon, Tube or Wall, the same as a trail. Particles work here too, and loop with the streaks.

Presets

With no trail selected, the top of the panel shows seventeen presets. Each one builds on what you have selected, with the same tools you would use by hand, so everything it makes can be changed after. Any preset works on anything: if your selection is not what the preset is made for, it still builds, and tells you what would suit it better. Every preset comes with particles that suit it, except four that are cleaner without: Car Taillights (a long exposure of car lights never shows anything flying off), Tron Light Wall (a clean wall of light), Ghost Dash and Smear Frames (the copies are the effect).

Render

At the bottom of the panel, whenever the scene has trails.

Render Check gets the scene ready to render. It fixes what has one right answer:

• records again any trail whose animation changed, or whose scene got longer;
• raises Cycles' transparent bounces to 64. Overlapping see-through trails and particles turn black where a ray runs out of them, and Blender starts at 8;
• adds the glow, once. If you remove it, it stays removed;
• turns on the viewport compositor, so the glow shows in Material Preview and Rendered;
• with smoke in EEVEE: turns on volume shadows (smoke looks flat without them) and makes sure EEVEE draws volumes as far away as the smoke goes.

It only ever raises a setting, never lowers one you set higher. Anything that is your call is left alone and listed under the button, like a path loop that will not repeat cleanly over the scene's frames, or a drawn look (Anime Fire, Water) under the AgX view, where the Standard view shows its colours brightest and truest. Render Check never changes your view. When nothing is left to fix, the panel says Ready to render, with any notes still listed above it.

Add Glow / Remove Glow: a soft glow round everything bright, made with a Glare node in the compositor (EEVEE has had no Bloom setting since Blender 4.2). Glow Strength and Glow Size are under the button.

Remove

The bin icon next to the trail's name deletes it, with what only it used: its recorded motion, its own material, and a curve a preset made for it. Never anything of yours. Ctrl Z brings it back.

When something looks wrong

Every setting

Trail

On the trail's modifier (the panel shows the ones that apply to its shape). Add Trail matches Width, Facing and Speed Gate to what you selected, so they may start somewhere else.

Particles

The same on trails and on path streaks.

Path streaks

On a path's modifier, plus the particle settings above.

Ghosts

Trail look

On the trail look node in the trail's material.

Ghost look

Smoke look

On the smoke node in a Smoke-shaped trail's material.