# Particle simulator | Emitters | Emitter | Particle systems | Particle System | Movement | Speed

If I select the slider and drag it with the mouse, it essentially changes the movement's speed to plus or minus infinity.

Pretty sure with the reset value of 200 having the slider in the middle, the far left should be 0 and the far right should be 400, not +/- infinity.

• Even clicking and dragging on the value, it seems happy going to a negative value. Is there any point to this? If you want to stop the speed to 0 you would prefer to just drag as far left as possible and over do it. This seems to happen on a few of the UI elements, forcing you to type things in.

In the VFX world, any negative value of most dynamic effects is pretty much the same as a positive value, so I'd like to understand why you'd not take it to 0 and stop?.

This is the latest version of the app.

As an example, looking purely at the Movement attribute:

Scale goes to +/- 1000 - I see no difference between them

Speed goes to +/- 2^32- I see no difference between them

The rest seem to make more sense.

• Moderator

Negative movement speed values become useful when using the lifetime graph. For example, I could make particles explode out from a point, come to a halt, then suck back in. With lifetime graphs this sort of effect is easier to set up than with forces. Also useful for movement speed variation. Let's say I have a base speed of 50 but a variation of 100. Now I won't have a bunch of particles at 0. Also, I am very glad speed doesn't top out at 400, since one of my recent shots uses a speed of 6000. Another recent shot used a particle speed of 14000. Sometimes I need a massive 3D space.

Negative scale values look mostly the same (flipped on an axis, perhaps) but, again, I may have a scale value of 50 and a variation of 100. Again, now I don't end up with a crapton of particles at size 0.

Every example above is given from things I have done, so I hope I have clarified the value and design logic of the current control setup.

• Making the speed span between 0 and some greater value in the settings would not necessarily cause the speed + variation calculation to be stuck at 0.

Same with the scale + variation calculation.

Understood on the speed being greater than 400 - the next bit of Axel's tutorial he set it to 800. But 2B? or -2B?

Anyway probably not a critical issue, just curious why you'd have a slider as a UI control when breathing on the mouse changes the value by around 100,000 at a time.

• Moderator

Agree, the slider is a pain, and I think you suggested before key modifiers to control slider rate of change--a great idea.

Since motion and scale variation is centered around the base value, a base of 50 with a variation of 100 gives a range of -50 to 150, so yes, mathematically non negative values only would imply nearly a quarter of my particles round to 0. Same with scale. Plus the axis flips on negative scale values yield more appearance variations as a side effect.

And, as noted, negative speed and the lifetime graph is how one would have particles explode out, come to a halt, stay motionless, then reverse--something that can't be done with forces.

In short, I am designing particle effects specifically around features of the sim you are finding useless. That may have come off as snarky, but is intended as matter-of-fact. :-)

• You use -2B speed? Interesting.

• Staff

I think its better to have more range than you need than to have less range than you need. I rarely use speed values above 5000, but it has happened. I think about 80,000 is the highest I've personally needed. So far.

As Triem mentioned, negative values on Scale will invert the texture; this will be more evident with some textures than with others.

• Moderator

Aaron, I haven't needed -2B speed, but I have certainly used negative values. Usually starting with a positive speed and using the lifetime graph to go negative. Particles explode out, stop, reverse, suck in.

I've also gotten use from negative scale values, since that "flips" the texture for more variety of appearance. Usually by creating a particle system, duplicating in, setting the copy to negative scale and changing it's seed.

I still agree that  Shift/Ctrl drag modifiers are useful. It's come up in the Wishlist and I wouldn't be surprised to see that in Update 5 or 6. Hopefully 5.