Simply Maya User Community - EXPRESSIONS FOR ALL! (knowledge tidbits)

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- - EXPRESSIONS FOR ALL! (knowledge tidbits) (https://simplymaya.com/forum/showthread.php?t=5601)

Thanks again mind-raper!

..and to post another variant for randomly-created particle attributes per a request in the MATRIX BULLET TRAIL thread
on how to get emitted particle instances (or even just particles)
to emit at random scale values:

Quote:

Originally posted by Rage:

Try this in a creation expression:

NOTE: you MUST add a radiusPP attribute to your particleShape, and apply this expression to that for this to work as you intend:)

The BOLD one is the one to use first, as it is what you asked for.
The rest are variants to try for fun:)

particleShape1.radiusPP = rand(.5,1)

OR

particleShape1.radiusPP = sin(time)

OR

particleShape1.radiusPP = sin(age)

Controlling speed for instanced Object

when you have instanced an object to particle specially a moving geometry its sometime very difficult to handle cause sometime movement of particles is higher than your instanced object or the other way your object speed is higher then particles(e.g you have created a crown moving through the scene and when you have instanced it to particle they are moving (sliding). there are other manual ways to fix it but i will show you how to do it with expressions, And For this we use a matching script with it you can query how much fast is....particle/object is moving and then according to it you can plug that value into your instanced object/Particles.

A real good way while you are using instanced Geometry, is to use Custom Attributes and then write the expression on the custom attribute and then plug that custom attribute into your instanced geometry.

for a situation where let say you have (crowd) walking animation
you instanced it with particles first you instance like you do normally with basic cautions thats you take before instancing any geometry

create custom attibute from Particle Attribute

goto

ADD DYNAMIC ATTRIBUTE
and add a attribute with you desired setting

customAge
float and Per Particle Array

you will see a new attribute in per particle array attributes named customAge

we'll write a custom expression as follow:-

float $Speed = mag(particle2Shape.velocity);
particleShape1.customAge = particleShape1.age * $Speed /10 (this number can differ as per your need you have to keep playing untill your object is no longer sliding !) ;

mag is for Magnitude ! see documentation for it !

if you are not getting a very good try low down da lifespan of the particle through the scene

hope it helps

enjoy instancing
:bannana:

Rock on m8! That's a keeper!

this one selects a random element from an array

proc int selectRandArrayVal(string $arr[])

{
int $randomInt = floor(rand(size($arr)))+1;
return $randomInt ;
}

:)

Cool thread btw

Alan

Hehe, I think mind_raper is raping all the gnomon video expressions

lolz
yeah..........
Cause not everyOne has the material so i think.....its helpfull ...!
but offcourse not all of them.....the are from different authors they are also mentioned !

Either way, an expression is an expression, so keep em coming guys! :)

Ok here's one which I just figured out.

Driving a shader attribute with distance from camera

Let's dig in to this with an example:

1. Create a lambert shader
2. Create a ramp texture (delete the place2dTexture node if it is created)
3. Connect the ramp's output to the lambert's color channel
4. Create a sampler info node
5. Create an expression with following code:

Code:

// NOTE: I'm using default object names here



vector $vPw = << samplerInfo1.pointWorldX, samplerInfo1.pointWorldY, samplerInfo1.pointWorldZ >>;

vector $vCamPos = << persp.translateX, persp.translateY, persp.translateZ >>;



float $fDistance = mag($vPw - $vCamPos);



ramp1.vCoord = $fDistance / 50; // The divider (50) is acting like a max distance value. You may need to adjust it depending on your scene size.

To test this, create a nurbs plane. Scale it in X and Z by 20. Apply the new lambert shader to it and render from different angles. You should see that the plane is red at near distance, green in the middle and blue in far distance. If you get repeats and banding then you need to adjust the divider in the expression.

WOW! Kinda like the Yuya Depth shader, only better!

Good one Kman!

I just figured out that controlling things based on the distance from camera is really usefull. For example HW particles (mainly points and streaks) are sized in pixels. So no matter how far they are, they will be (HW) rendered the same size -> not exactly realistic looking. If you add a runtime expression which scales the opacityPP based on the distance from the current camera it will look a lot better.

Example:

Code:

vector $vPPos = lpos; // last position of the particle

vector $vCPos = << persp.tx, persp.ty, persp.tz >>; // current camera position

float $fDistance = mag($vPPos - $vCPos) / 20; // particle's distance from camera (scaled to be in range of 0 - 1)

opacityPP = 1.2 - $fDistance; // the opacity will be at least 0.2 but degrades when the distance increases from the cam

Again you need to play with the divider (20) to scale the opacity reduction to fit the size of your scene. The "1.2" on the last line determines the overall opacity level of all particles (you want to keep this greater than 1.0)...

And with this expression, who says a lot of rain spoils a shot?

Good one again Kman!

yeah that helps in densed(populated) particles scene where it need lots of camera adjustment will cut down lots of time !

I don't care from where they come here

Hi.

Cool thread !
I'm new here and I'd learned alot from these expressions.
I don't care from where they come here, all of them are good for me. Thank mind_raper and everyone.

Why the thread had stoped ?

Sorry about my poor English.

Hasn't really stopped, just slowed down a bit because folks are a little busy.
It is a "sticky" thread so that way it is always at the top for reference:)

Feel free to post any questions, and we will see if we can help:)