Lesson 04
Parts that pump
A wing or a leg that moves is a barrel firing a harmless speck, because every barrel that fires slides back on the shot.
What you see
Two wings that beat while you hold fire, one up while the other is down. There is no animation system in the editor. There is only recoil: every barrel that fires slides back along its own axis on each shot, and that slide is the whole animation.
The trick
Draw the wing as a barrel, then make it fire something nobody will notice: a White speck with almost no damage, size or lifetime. Hold fire and the wing pumps at the barrel's reload rate. Put Fire delay 0.5 on its partner and the pair alternates.
Two conditions, learned the hard way:
- The barrel must be at least about 0.5× wide (22 units). A 0.3× barrel pumps so little you cannot see it, however long it is.
- Its muzzle end must be uncovered. The slide is along the barrel, so a part painted over the tip hides the movement, as the body hides the root. Animate the last segment of a limb, not one buried under a knee.
Numbers that matter
| Speck field | Value | Why |
|---|---|---|
| Damage, Penetration | 0.01, 0.2 | So it hurts nothing and dies on contact |
| Bullet size, Bullet speed, Lifetime | 0.15, 0.1, 0.1 s | A dot that vanishes at the muzzle. White specks read as sparkle |
| Recoil, Knockback | 0, 0 | So the wing beats do not push the tank around |
| Reload | 0.5 | Beat rate: lower is faster, and costs more budget |
| Fire delay | 0 and 0.5 | The pair alternates; 0.25 steps four legs round |
Gotchas
- Every pumping part is a firing barrel and counts against the lobby's budget (lesson 15): 120 entities a second with Reload maxed. Ten pistons at Reload 0.5 can be refused. Put the Reload stat cap to 0 on tanks that move a lot.
- The pump only shows while the barrel fires: on click, or always with Always fire.
- Thin and moving are at odds. A limb is either slender and still, or about 0.5× wide and pumping.
- The speck is a real bullet for a tenth of a second; it is not drawn with the team colour because its projectile has a colour of its own (White).
Where we used it
