Two components draw flat strips, the way Unity’s Line Renderer and Trail Renderer do:
- Line Renderer: a line through a list of points. Use it for aim guides, laser beams, cables and paths on a map.
- Trail Renderer: a trail through where its object has been in the last few seconds, thinning and fading towards the tail. Use it for rockets, sword swings and balls in flight.
Both turn to face the camera (Alignment View), so they always show their full width. Alignment Transform Z lays one flat instead: it faces along its object’s forward axis, like a line painted on the ground. Turn the object to face up (rotation 90, 0, 0) for that.
Each draws through a hidden child object that holds its mesh. That object isn’t saved and doesn’t show in the Hierarchy. So a trail can go on a ball’s own object without replacing the ball’s mesh.
Line Renderer
| Field | What it does |
|---|---|
| Use World Space | On: the points are in the world. Off: they are relative to the object, and the line moves and turns with it. |
| Loop | Joins the last point back to the first. |
| Start Width, End Width | Width at the first and last point, in metres. |
| Start Color, End Color | Colour at the first and last point, blended between. An alpha below 1 makes the line see-through. |
| Alignment | View or Transform Z (see above). |
| Texture Mode | Stretch: the texture runs once along the whole line. Tile: it repeats every Tile Length, so it keeps its size as the line grows. |
| Tile Length | With Tile, how long one repeat of the texture is, in metres. |
| Dash Length, Gap Length | Draws the line in dashes this long with gaps this long between, in metres. Dash Length 0 is a solid line. A dash as long as the width makes square dots. |
| Material, Texture | What to draw it with. With neither, it draws in its colours. |
| Unlit, Cast Shadows | Lines are unlit and cast no shadows by default. |
| Glow | Makes it glow in its own colours, through bloom. |
| Positions | The points, as a list: set its size, then each point’s X, Y and Z. Saved with the scene. |
| Children As Points | Draws the line through the object’s children, in order, instead of Positions, so you can drag the points in the Scene view. |
Scripts can set the points too (positions is a List<Vector3>, so anything a list does works on it as well):
let line = GetComponent<LineRenderer>();
line.SetPositions(scope Vector3[](start, end)); // replaces every point
line.PositionCount = 3; // grows or shrinks the list
line.SetPosition(2, tip);
let length = line.Length;A golf-style aim guide is a two-point line from the ball along where the camera faces, longer as the shot charges:
var direction = camera.Transform.Forward;
direction.y = 0;
direction = direction.Normalized;
let start = ball.Position + direction * (ballRadius + 0.05f);
aim.SetPositions(scope Vector3[](start, start + direction * Mathf.Lerp(0.5f, 3, power)));
aim.startColor = .(1, 1, 1);
aim.endColor = Color.Lerp(.(1, 1, 1, 0), .(1, 0.2f, 0.1f, 0), power);Textures
The texture is laid along the line: the image’s width runs along the line and its height across it. With Stretch, the image is stretched once over the whole line. With Tile, it repeats every Tile Length metres, so arrows or chevrons keep their size however long the line gets. The texture’s alpha makes the line see-through where the image is clear, so an image of one arrow on a clear background gives a row of arrows. Start Color and End Color tint the texture.
Dotted and dashed lines
Set Dash Length and Gap Length, with no texture needed. For dots, make the dash as long as the line is wide:
aim.startWidth = aim.endWidth = 0.08f;
aim.dashLength = 0.08f; // square dots
aim.gapLength = 0.12f;Dashes follow the line’s corners and blend its widths and colours like a solid line.
Trail Renderer
| Field | What it does |
|---|---|
| Time | How long a point stays in the trail, in seconds. |
| Min Vertex Distance | How far the object moves before the trail gets a new point. Smaller is smoother but costs more. |
| Start Width, End Width | Width at the object and at the tail. |
| Start Color, End Color | Colour at the object and at the tail. The default fades to fully see-through. |
| Emitting | Off: no new points are added and the trail fades away. It starts again when turned back on. |
| Show In Editor | Also draws in the editor while not playing. |
| Alignment, Texture Mode, Tile Length, Dash Length, Gap Length, Material, Texture, Unlit, Cast Shadows, Glow | As for Line Renderer. |
Call Clear() after a teleport or respawn so the trail doesn’t streak across the level. PositionCount and GetPosition(i) (oldest first) read the trail’s current points.
Limits
- Facing follows one viewer each frame: the game’s camera, or the Scene view while editing. In the editor while playing, lines face the game camera, so in the Scene view they can look edge-on.
- Sharp corners narrow a little, because there are no extra corner vertices. There are no rounded end caps.
- A line or trail with any alpha below 1 is drawn see-through, after everything solid.
- Each is rebuilt on the CPU every frame. Hundreds of points are fine; tens of thousands are not.
This guide is docs/lines-and-trails.md in the engine’s repository. Spotted a mistake? Open an issue.