Understanding Clamp Expression

[cspears2002]

I am going through the particle shockwave tutorial in Houdini. In the tutorial, I create a Source POP called shockwave_emitter_source. In the Birth tab, I put the following expression in the Impulse Activation parameter:

((clamp($F, 2, 3*20+20/2)%20)<=1)

What is this expression doing? Why did the author use 3*20+20/2 ? Couldn't the same result be achieved by replacing that with 70?

particle_shockwave.hipnc

[rdg]

I am going through the particle shockwave tutorial in Houdini. In the tutorial, I create a Source POP called shockwave_emitter_source. In the Birth tab, I put the following expression in the Impulse Activation parameter:

((clamp($F, 2, 3*20+20/2)%20)<=1)

What is this expression doing? Why did the author use 3*20+20/2 ? Couldn't the same result be achieved by replacing that with 70?

From the help:

A clamp function clamps the value between min and max.

The input value is cut off if going over max and limited if falling below min.

I guess the 3*20+20/2 is the process of finding an appropriate value.

As there is no variable in this term you could easily replace it.

-- ---

This didn't explain the expression, though:

the clamp turn the current frame number into a number beweteen 2 and 70.

the '%20' applies the modulus operation resultung in a number between 0 and 19.

the '<=1' is a boolean term that results in a 1 if the expression so far is below or equal 0. The rest of the time it returns 0.

->

every 20th frame there is a burst of paricles, but only after frame 1 and before frame 70.

-- ---

Georg

Edited May 9, 2007 by rdg