Exercise 15: A shockwave that bends the air

Purpose. To send a ring of bent air out from the explosion of Exercise 10, as a shockwave does.

A shockwave has no colour and no shape of its own. It is seen only because the world behind it looks bent for a moment, as through moving glass. No particle can show that. The Distortion emitter bends the picture itself.

Before starting

• The Explosion folder from Exercise 11 is in the workspace.
• One new ordinary Part named Shock is inside the folder, at the centre of the explosion.
• The camera looks at the explosion from 20 to 40 studs away, with scenery behind it. A bend shows only where there is something to bend.

Procedure

Steps 1, 5 and 6 repeat earlier exercises.

Step	Control	Action	Result
1	Shock	Select. Press ▾ beside Transform, then Transform as Distortion.	Shock turns invisible. The Properties panel shows the sections of a Distortion, with Emission, Field and Screen open. The Emit box reads 1.
2	HUD ▸ Emit button	Press	For half a second the view around Shock swells and settles. There is no clear ring yet.
3	Properties ▸ Field ▸ Wavelength	Enter 0.15	No change yet.
4	Properties ▸ Field ▸ Speed	Enter 8	No change yet.
5	Properties ▸ Emission ▸ Lifetime	Enter 1	No change yet.
6	HUD ▸ Emit button	Press	A thin ring of bent air starts at Shock and spreads outward across the view for one second, fading as it goes.
7	Properties ▸ Field ▸ Amplitude ▸ ⋯	Press. Set the left-hand keypoint to 1 and the right-hand keypoint to 0. Press Apply.	No change yet.
8	Explosion	Select, then press Emit on the HUD	The explosion plays with its flash and jolt. The ring races out from its centre, strong at first and gone by the edge of the view.

NOTE

A distortion is seen by one player only: the one whose machine fires it. It is the same rule as for the flash and the jolt of Exercise 11.

NOTE

Distortion is meant for short bursts. In a published game it looks best when the experience allows the Mesh and Image APIs, under Game Settings, Security. Without that, a simpler and blockier version is shown.

What the steps did

A Distortion emitter creates nothing in the workspace. For its Lifetime it bends the picture of the 3D world. The Part is an invisible marker for where the bend is centred. Distances on screen are measured in screen heights: 1 is about the height of the view.

Field chooses the shape of the bend.

Field	What is seen	Rows it uses
Ripple	One ring that spreads out from the centre.	Amplitude, Wavelength, Speed
Wave	Straight waves that cross the whole view.	Amplitude, Wavelength, Speed, Direction
Noise	An uneven shimmer that drifts across the view.	Amplitude, Noise Scale, Speed, Direction
Bulge	A still lens that pushes the picture outward.	Amplitude, Lens Radius
Pinch	The same lens, pulling inward.	Amplitude, Lens Radius

Rows that the chosen Field does not use are hidden.

Row	Starts at	What it sets
Field ▸ Amplitude	0.5	How strongly the picture is bent, over the life of the effect.
Field ▸ Wavelength	1.5	For a Ripple, the thickness of the ring. At 1.5 the ring is wider than the view, which is why step 2 showed a swell and no ring.
Field ▸ Speed	3	For a Ripple, how fast the ring grows. A Speed of 8 is 0.8 screen heights a second.
Screen ▸ Epicenter	WorldPoint	WorldPoint centres the bend on the Part, wherever it appears on screen. ScreenCenter centres it on the middle of the view.
Screen ▸ Falloff	0	The distance at which the effect has faded to nothing, as for Camera Shake. At 0 there is no fade with distance.
Screen ▸ Strength	1	A plain multiplier on Amplitude.
Screen ▸ Transparency	A graph from 0.3 to 1	How present the bend is, over the life of the effect. At 1 the effect cannot be seen. The starting graph ends at 1, so the effect ends without a jump.

Several distortions at once are added together.

If the result differs

Symptom	Cause	Action
Nothing bends	There is nothing behind the effect to bend, or Shock is behind the camera.	Look at the explosion with scenery behind it.
A swell, but no ring	Wavelength is still 1.5.	Repeat step 3.
The ring is gone before it has travelled	Lifetime is still 0.5.	Repeat step 5.
The effect ends with a jump	The Transparency graph no longer ends at 1.	Set its right-hand keypoint to 1.
The ring does not fire with the rest	Shock is not inside Explosion.	Drag it into the folder.

Variations

Change	Result
Field Noise, Mode Animate, Loop on, Amplitude 0.15, Noise Scale 6, Direction 90, Screen ▸ Transparency 0.6, Falloff 60	A heat shimmer that rises over a fire, seen only from near it.
Field Wave, Epicenter ScreenCenter, Mode Animate, Loop on, Wavelength 0.5, Speed 2	The whole view wobbles, as under water.
Field Pinch, Lens Radius 0.3, an Amplitude graph that rises from 0 and returns to 0	The view is pulled toward the Part and let go.
HUD ▸ Delay 0.05 on Shock	The ring leaves a moment after the flash.
Screen ▸ Falloff 100	From farther away the ring is weaker, and beyond 100 studs it is not seen.

Log

New in this exercise	Transform as Distortion. Field. Wavelength. Speed.
Done before	Transform as (Exercises 11 to 14). Lifetime (many times). A graph that falls to 0 (Exercises 4, 5, 8 and 11). A Folder fired as one (Exercises 10 and 11). Falloff (Exercise 11).
Carried forward	Keep Explosion.