Exercise 7: Sparks that stay on a moving blade

Purpose. To make the sparks of Exercise 3 appear at another object and follow it as it moves.

An effect is seldom wanted where its emitter happens to sit. Sparks belong on the edge of a blade, dust under a foot, a flash at a muzzle. The object moves, and the effect has to go with it. A link tells an emitter which object to follow.

Before starting

• The sparks emitter from Exercise 3 is in the workspace. Auto-emit is off.
• The workspace also holds one new, ordinary Part, a few studs away from the emitter. Name it Blade. It stands in for the object the sparks should follow. Do not transform it.

Procedure

Steps 1, 6 and 11 repeat earlier exercises.

Step	Control	Action	Result
1	The sparks emitter	Select	The HUD and the Properties panel show it.
2	Properties ▸ Link	Expand	The Link rows show.
3	Properties ▸ Link ▸ Link Dir. ▸ *	Press	A small box opens and asks for an instance. Studio’s selection is cleared.
4	Blade, in the viewport or the Explorer	Click	The box names Blade as the instance.
5	The box ▸ Set	Press	The box closes. The emitter is selected again. The Link Dir. row shows the path to Blade, and the Link row reads Object.
6	Properties ▸ Emission ▸ Enabled	Switch on	The sparks appear at Blade, not at the emitter.
7	Blade	Select it and drag it across the viewport, then select the emitter again	The sparks in flight travel with Blade. New sparks appear wherever it now is.
8	Properties ▸ Link ▸ Link Mode	Set to Weld	No change while Blade is still.
9	Blade	Select it and rotate it, then select the emitter again	The shower turns with Blade. Sparks in flight swing round with it, as if fixed to it.
10	Properties ▸ Link ▸ Link Axes ▸ Pos Y	Click to switch off	The sparks follow Blade sideways but stay at the emitter’s own height.
11	Properties ▸ Emission ▸ Enabled	Switch off	The sparks stop.

NOTE

The emitter itself does not move. A link changes where its particles appear and what they follow. The emitter can be kept anywhere, for example in a folder of effects away from the scene.

NOTE

While the box is open, the Properties panel does not follow the selection. Press Cancel to close the box without changing the link, or Clear to remove the link.

What the steps did

Link Dir. holds the object to follow. It accepts a Part, an Attachment, a Model, a Bone or the camera. Setting it switches the Link row to Object. The Link row can also be set to Camera, to follow the camera with nothing picked, or to None, to switch the link off.

A link does two things. Particles are made at the linked object. Then, every frame of their life, they are carried along as it moves.

Link Mode decides how much of the object’s movement the particles take up.

Link Mode	Particles in flight follow its position	Particles in flight turn with it	Use for
Follow	Yes	No	Dust under a moving foot. The shower keeps pointing the way the emitter points.
Pivot	Yes	No, but each particle starts out facing the way the object faces	A muzzle flash that takes its aim from the barrel.
Weld	Yes	Yes	Sparks fixed to a swinging blade.
WeldWithoutRotation	Yes, swinging round it as it turns	No, each particle stays upright	Markers that circle a spinning object without tumbling.
RigidLocal	No	No	A burst that starts at the object, facing its way, and is then left behind.

Follow is the starting value.

Link Axes has six buttons: Pos X, Y, Z and Rot X, Y, Z. Each one switched off stops that part of the object’s movement from reaching the particles. For that axis the particles keep the emitter’s own value. With Pos Y off, an effect follows a character across the floor and never leaves the floor when the character jumps.

If the linked object is removed while particles are in flight, they carry on from where it last was.

If the result differs

Symptom	Cause	Action
The box says the pick is not allowed	The instance clicked is not a Part, Attachment, Model, Bone or camera.	Click Blade.
Sparks still appear at the emitter	The Link row reads None.	Set it to Object.
Sparks fly off at an odd angle in Weld or Pivot	The emitter is itself rotated. Its rotation is added to that of the linked object.	Set the emitter’s Orientation to 0, 0, 0 in Studio’s Properties window.
Rotating Blade has no effect	Link Mode is Follow, which ignores rotation.	Set Link Mode to Weld.

Variations

Change	Result
Put an Attachment at the tip of Blade and link to the Attachment	The sparks come from the tip, and stay on it as Blade swings.
Link set to Camera, Link Mode Weld	The effect is made at the camera itself and moves with the view. Give it a Spawn ▸ Position a few studs forward to see it.
Link Mode RigidLocal, then Emit	Each burst starts at Blade, takes its direction, and stays where it was fired.
Link Mode Weld, Link Axes Rot X and Z off	The shower turns left and right with Blade but does not tip over with it.

Log

New in this exercise	Link Dir. and its * picker. Link Mode. Link Axes.
Done before	Selecting an emitter (every exercise). Enabled (Exercises 1, 2, 4 and 5). Expanding a section (Exercise 5).
Carried forward	Keep the sparks emitter. Exercise 9 uses it again.