CGTalk - particle emission

Octagon

03-13-2003, 10:29 AM

Hi there,

this is an older thread that i started some time ago. Since no one answered I want to give the topic another try since I think what I want to do should be rather common and someone more experienced has to know ...

I want do to a surface that randomly emits a load of particles around the same uv location on the surface on a given interval. in the next interval the emitter should emit particles on another uv location with different rate and speed.

i found a decent way to randomize rate and speed of the emitter in intervals
but how can i make my emitter emit from approximately the same uv value as it did the frame before ? this would accomplish what i mean by "a load of particles" (for the lack of a better word).

matthias

mark_wilkins

03-13-2003, 08:06 PM

Here's what I did:

Make a surface emitter.

On the emitter, turn on the Need Parent UV attribute.

On the particle object, use the General button to add the parentU and parentV attributes.

These attributes give you the U and V from which the particles were emitted.

Make a creation expression for the particles that tests whether U and V are within the appropriate range. If not, set lifespanPP to 0, which suppresses emission of the particles.

Here's the creation expression I used. With the object I was using, this emitted particles first from one side and then the other:

float $ulow;
float $uhigh;
float $vlow;
float $vhigh;

if (frame < 100)
{
$ulow = 2;
$uhigh = 3;
$vlow = 2;
$vhigh = 3;
}
else
{
$ulow = 1;
$uhigh = 2;
$vlow = 6;
$vhigh = 7;
}

if (!((particleShape1.parentU > $ulow) && (particleShape1.parentU < $uhigh) && (particleShape1.parentV > $vlow) && (particleShape1.parentV < $vhigh)))
{
particleShape1.lifespanPP = 0;
}

-- Mark

Octagon

03-16-2003, 04:31 PM

Mark, thanx for your insight! I figured the parentU and V attrs could be helpful for my task but couldn't quite figure out how to use it. Thanx again!

matthias

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