Exercise 11: A flash and a jolt

Purpose. To make the explosion of Exercise 10 flash the screen and shake the camera.

Fire and smoke are things in the world. A strong explosion is also felt: the picture whites out for an instant and the view jolts. Neither is a particle that travels. One is a screen effect, the other moves the camera. Both are made, timed and fired like any other emitter.

Before starting

The Explosion folder from Exercise 10 is in the workspace. Add two things to it, in the Explorer:

• A new ColorCorrectionEffect, named Flash. It can stay in the folder. It does not need to be in Lighting.
• A new ordinary Part, named Jolt, placed at the centre of the explosion.

Procedure

Steps 1 to 4 repeat earlier exercises on a new kind of emitter.

Step	Control	Action	Result
1	Flash	Select, then press Transform	The Properties panel shows the sections of a ColorCorrection emitter, with Emission and Appearance open.
2	Properties ▸ Appearance ▸ Brightness ▸ ⋯	Press. Double-click the left-hand keypoint, enter 0.5 for Value. Press Apply.	The graph falls from 0.5 to 0.
3	Properties ▸ Emission ▸ Lifetime	Enter 0.2	No change yet.
4	HUD ▸ Emit button	Press	The whole viewport brightens and returns to normal within a fifth of a second. The Emit box already reads 1.
5	Jolt	Select	The Transform button appears, with a small ▾ button beside it.
6	▾ ▸ Transform as Camera Shake	Press ▾, then click the entry	Jolt turns invisible. The Properties panel shows the sections of a Camera Shake, with Emission and Shake open. The Emit box reads 1.
7	HUD ▸ Emit button	Press	The viewport shakes at full strength for half a second and stops dead.
8	Properties ▸ Shake ▸ Amplitude ▸ ⋯	Press. Set the left-hand keypoint to 2 and the right-hand keypoint to 0. Press Apply.	No change yet.
9	Properties ▸ Shake ▸ Falloff	Enter 80	No change yet.
10	Explosion	Select, then press Emit on the HUD	Fire, smoke, flash and jolt play together. The shake starts hard and dies away. Seen from farther off, it is weaker.

NOTE

A screen effect and a camera shake are seen by one player only: the one whose machine fires them. In the editor that is you. In a game, each player’s own machine must fire the effect for that player to see it.

CAUTION

Screen effects from one emitter stack. With Enabled on, Rate 10 and Lifetime 1, about ten are active at once and the result is far stronger than one. For a single flash use the Emit box with a count of 1.

CAUTION

The plugin puts no limit on camera shake and has no setting that lets a player reduce it. A game that wants to offer that choice must decide for itself whether to fire the emitter.

What the steps did

A ColorCorrection emitter makes a short-lived duplicate of the effect and runs its graphs over the Lifetime. Its four rows are Brightness, Contrast, Saturation and TintColor. Each starts at the value the effect had when it was transformed. Brightness, Contrast and Saturation can go below 0 as well as above it.

Transform as is the list behind the ▾ button. It shows only when the selection includes an ordinary Part that has not been transformed. It turns a Part into one of five special emitters. The Part becomes an invisible marker for where the effect comes from.

A Camera Shake creates nothing in the workspace. It moves the camera for its Lifetime and puts it back exactly where it would have been.

Row	Unit	What it sets
Amplitude	Studs	How far the camera is pushed, over the life of the shake. The push at any instant is up to about half the value.
Rot. Amplitude	Degrees	How far the camera is tilted. It starts at 0.6.
Frequency		How fast the shake wobbles. 10 is a nervous rumble, 2 a slow sway.
Falloff	Studs	The distance from the marker at which the shake has faded to nothing. At 0, the shake is felt at full strength everywhere.

With Falloff at 80, the shake has full strength at Jolt, three quarters at 20 studs, half at 40 and none from 80 studs outward.

Several shakes at once are added together.

If the result differs

Symptom	Cause	Action
No ▾ button at step 5	The selection has no ordinary, untransformed Part in it.	Select Jolt alone.
Nothing flashes at step 4	The Emit box reads 0.	Enter 1.
The flash ends with a jump	The Brightness graph does not end at 0.	Set the right-hand keypoint to 0.
The viewport stays bright	Linger holds the last frame, or Enabled is on.	Set Linger to 0 and switch Enabled off.
The shake is the same at any distance	Falloff is 0.	Repeat step 9.
The flash and the jolt do not fire with the rest	They are not inside Explosion.	Drag them into the folder.

Variations

Change	Result
Transform a BlurEffect, Size graph from 20 to 0, Lifetime 0.3, Emit 1	The view blurs at the blast and sharpens again.
On Flash, a Saturation graph from 0 to -1, Mode Animate, Linger 2	The colour drains from the view and stays grey for two seconds.
On Flash, a TintColor gradient from orange to white	The flash is tinted like firelight.
On Jolt, Rot. Amplitude 2	The view also rocks from side to side.
On Jolt, Mode Animate, Loop on, Amplitude 0.15, Frequency 18, Falloff 40	A steady engine rumble, felt only near the marker.
On Jolt, HUD ▸ Delay 0.1	The jolt arrives a moment after the flash.

Log

New in this exercise	A ColorCorrection emitter. Transform as. Camera Shake: Amplitude and Falloff.
Done before	Transform (seven times). A graph that falls to 0 (Exercises 4, 5 and 8). Lifetime (Exercises 2, 6, 9 and 10). The Emit box and button (Exercises 3, 6, 8, 9 and 10). A Folder fired as one (Exercise 10).
Carried forward	Keep Explosion.