Raindrops

In this tutorial we are going to take a look at setting up a bit more complicated Particle Flow effect. That of falling rain, with all the bells and whistles. Rain does more than fall after all, it falls, hits, splashes, runs, drips, collects, and trails.

Let's try to get a single Particle Flow that incorporates all that rain might do in real life. Again this one is not for the faint of heart, so if you are just beginning you may want to try some of the simpler ones first, there warning ended, onward!

We start with an empty scene, and we will need to create several things before we get going.

First we will need something to represent the ground, this something might as well also serve an actual purpose other than visual so we'll use a deflector.

Go to your create tab, and then over to the spacewarps button.

In the dropdown menu that defaults at Forces, change it to Deflectors.

We want just the normal Deflector out of all these others to choose from, this one is a flat surface deflector that will be whatever size we draw it out as.

I'm going to draw mine out in the top view so the ground is facing the correct direction, and I'll center it using the coordinates at the bottom of your screen by setting it to 0.0 in all three xyz locations. Like this:

We will select the Deflector and in the Modify tab make the settings just like this.

Set your Bounce at around 0.4, we don't need the drops reflecting off into space now do we, just a bit will do fine.

Variation at 33% to allow for some drops to bounce a higher or lower than others, variety!

Chaos at 80%, rain is not exactly predictable after all.

I made the Height and Width of my deflector 200 in both, give us a nice square patch of ground to work with for this.

That will give us some ground to start with, let's go ahead now and make the first portion of our particle system.

Press 6 on your keyboard to open up Particle View, you can also get here by going to the Graph Editors menu and finding Particle View there.

You should be fairly familiar with this view by now, if you aren't I recommend backing up and doing a simpler Particle Flow tutorial first, as I do not plan on going into great details on everything in this view like I have in earlier ones.

If you are in fact ready for this then you already know what this view is for, and what each partition represents so we can dig right in.

First we need to create our PFlow by dragging an Empty Flow to the open stage area.

The second you drag an empty flow into the chart area, you should see an orange PFlow icon show up in your scene at 0,0,0. Lets modify this a bit before we go too far. Select the icon and go to your Modify tab.

First we might as well rotate it into a position that will work for rainfall, Make sure the arrow is pointing down.

Then Move the icon up, you can be exact if you grab your move tool, and in the coordinates area at the bottom again, simply type 200.0 in the Z axis.

Then with the icon still selected go to your Modify Tab to adjust the final settings.

Make your icon's length and width match your ground deflector.

And let the viewport display 100% of the particles so we know what we are dealing with.

Then go back to Particle View and drag out a Birth to the open stage area.

We'll select the Birth and adjust its settings now to the right of the stage area.

We will need a decent number of frames to see our rainfall, I have set the emit start at 0 and the stop at frame 300. If you have not extended your timeline to accommodate a larger animation you might want to do that now as well.

I am going to start with 600 particles, we can always increase it later once we have the full working particle system.

Next, drag out a position icon from the list and drop it right under the Birth inside the Event01 box.

This means that the particles will be emitted by the orange icon itself and not an object or anything else. We can leave it set to its defaults for now since Volume is what we want. Which makes the rain fall from the entire surface of the icon and not just the pivot point or edges, etc. If you scrub down your timeline you should now see particles appearing along the surface of the icon.

They don't however, fall ... so far all they do is begin to appear. We can make them fall in a variety of ways including speed settings, but for a bit more reality to our scene, let's think about how rain falls in the real world. That's right, Gravity! Let's make some.

Go to your create tab, and find the space warps button again. Move the dropdown from Deflectors back to Forces and click the Gravity button. I recommend creating your gravity in the top view so that the arrow points down, gravity going to the left is just silly afterall.

Then go to your modify tab with your gravity selected to modify its settings.

We want our drops to just kind of casually drip from the sky, so let's reduce the strength of our gravity to something a lot smaller like 0.1.

As long as the arrow on the icon is pointing down towards the ground, we are done with these settings.

Go back to particle flow, and drag a Force from the list to below the Position Icon.

Then add the Gravity to the settings off to the right.

Now your particles should start to fall as you scrub down your timeline.

The tick marks just aren't doing it for me as far as looking like rain, let's change the settings for our Display 01 which should be the last thing in our event window in Particle View. Let's change it to lines.

You can also adjust the color the lines display as from here as well, I made mine white.

Much better!

Now, we'll make them collide with our ground.

Drag a Collision Spawn from the list in particle view, and place it at the end of the Event01 box.

We'll change quite a few settings for this one, first of which is to add our deflector:

This should be defaulted

Add our deflector to the list here

Make sure that Spawn on First collision and Delete Parent are selected

We want all our rain to splash, so leave 100.0% of the particles spawnableLet's make it spawn 10 new particles on impact.

Reduce the inherited velocity to 30.0 so they only bounce with a fraction of the speed they started with.Variation of 10% allows for some differences in the splashes.Divergence of 12.0 lets them spread apart a bit as they fracture into 10 new particles. Increase this if you want them farther apart.

At about this part, lets add something else between our rain, and our ground so that we can get some more interactions happening for our particles. Lets add something for them to drip down and fall off of, we'll add a sphere and another deflector.

I have added a sphere in between and located it at 0,0,75. So it sits directly in the middle of our ground and our rain spawner.

Next we'll need to add another deflector, back under spacewarps find the one labeled UDeflector.

This one is an interesting deflector because it allows any mesh object to become the surface of the deflector. Draw it out anywhere in your scene, and then with it selected go to the modifier tab.

Click the Pick Object button and select the sphere we just made as the Object Based Deflector.

Reduce the bounce to 0.6 with a 30.0% variation

Chaos at around 35%

Friction at 100% to reduce the speed the drops have when they do make contact with our in-between surface on their way to the ground.

Then all you have to do is go back to your Particle View, and add that deflector the Collision Spawn as well as the original Deflector.

Now we will get a splash no matter which surface our drops hit, splashes aren't enough! Let's have some real fun with this.

Hold down your shift key, and hover over the Force in our first Event list. When you see the mouse point with a + sign above it click and drag while holding shift and then drop it in the empty grey area next to our first event box. Like this:

Once you let go the Clone Options box should appear, make sure to select Instance, and then click ok.

We have just duplicated our gravity force into a new event, we are going to connect the blue dongle from our Collision spawn, to the empty circle in this event. This will tell our splash particles we just made to listen to gravity and move on to the next event.

In this new event we are going to define the dripping and/or splash of our raindrops running down the surface of our sphere.

Grab a Speed By Surface from the list below and add it below our Instanced Force02 in the new event.Make your settings match mine for the new Speed By Surface.

We don't want the first splash to move away from the sphere very fast, so make the speed down to 8.0 with a variation of 20.0.

Add the Sphere we made to the Surface Geometry, making the surface of the sphere control the speed of the splashes.

Make your Divergence 180.0 so the splashes can travel in all directions.

Then find a Collision from the list in Particle View and add it to below the Speed by Surface.

Add the UDeflector to the settings for this new collision event.

Then make sure Collides and Bounce are set here.

Next Add a Collision Spawn under the regular Collision we just made and add the Ground Deflector to it in the settings.

------>

Make your settings match mine to the left here.

This is where our rain drops will give us a secondary splash if they hit the ground.

You can just delete any extra displays that have been created in this new event.

Next find a Split Amount in the list of events in Particle View, and drag it out to the empty stage area, and connect the blue dongle from our first Collision in the second Event box to the empty circle above our Split. I told you this was going to get a lot more complicated! ;)

This new event will be where our drops that hit the sphere split up and some become splashes, and some become drips.

This split will determine based on the % we provide how many drops that hit our sphere will splash, and how many will go on to drip down the side of the sphere. We can call it a Drip Decider.

Select the Split Amount and adjust its settings to the right.

Make the Ratio% at 10.0. This means 10% of the particles that hit the sphere will be sent on to become drips.

Then find a Send Out in the list in Particle View and add it directly under the Split Amount.

Then connect the blue dongle that comes with our new Send Out (all) right back to the previous event. Making all the other drops that don't become drips to get recycled into our splashes to try their luck again.

As for our Split Amount (10%) we are going to send it onwards to a new event that will dictate the dripping action.

Lets copy our force again, to a new event below and to the right of our Event03, the same way we did before by holding shift and dragging it. This time don't select Instance though, make this one a copy so we can change it independant of the original.

Connect the blue dongle from our Split Amount to this new Event.

And in the settings for our Copy of Gravity, change the influence to 1500.0 instead of just 1000.0%

This makes our 10% drip particles in this new event listen to a bit stronger gravity for added effect.

Then add another speed by surface below the new force.

------> Set the new Speed By Surface settings like I did here.

Control Speed Continuously this time from the top drop down.

Speed 12 with variation of 8.0

Add the sphere as the Surface Geometry.

Set the Direction drop down menu to Parallel to Surface

And set the Acceleration Limit to 300.0

Then lets add some more collisions!

Add another regular collision, and assign the UDeflector in the settings. Leave it set to default Collides and Bounce.

Under that add a Spawn, and then adjust the settings like the image to the right. --- >

Set the spawn to Travel by Distance and set the Step Size to 0.5. This is going to spawn our dripping trails.

Make them 100% spawnable and make their offspring 2 with 0.0 variation

Under Speed settings make the inherited very low, at 1.0. No variation, and a Divergence of only 3.

This will ensure that the trails follow in almost a straight line behind the original.

Below our new Spawn, add an Age Test and match the settings like this:

------>

Next we are going to find a Delete event in the list and drag it out to the empty stage area creating yet another new event box. Place this one off to the left side of our current one.

--->

This will ensure that the trailing drips don't go on forever, but rather end after 25 life, give or take a variation of 5. Then make sure you connect the blue dongle from our Spawn in the last event box to this new event. like above:

Now that we've made the drips capable of existing, we have to tell them how long to remain drips before once again leaping off of our sphere surface and heading towards their fate which is splashing into the ground.

To do this we are going to make another instance of our initial gravity (not the copy which we changed, the first one)

Hold shift again and find our first Force. Then drag it and copy it to the empty stage area somewhere below and to the right of our Event04 box. Make sure to select Instance for this one again.

Then connect the blue dongle from our Collision in Event04 box, to this new event. Like above:

Also go ahead and connect the Age Test dongle to this same event.

This will make it so that after our trails live for 40 frames (give or take 10) they will again fall off the sphere by listening to gravity all over again.

In order to give them a little push off the sphere, we are going to now add another Speed by Surface under our new Force.

Adjust the settings like the ones to the right. ----->

Set Speed Once

A low speed of only about 4.0 or less and a variation of 5.0.

We only want to give them a little push, not a rocket takeoff.

Add the Sphere to the list of Surface Geometry.

And under Direction make it Surface Normals

with a Divergence of 25.0 which means it can take off in several newdirections.

Now most drips pick up volume as they drip down the surface of things, collecting other droplets of water as they travel.

If we want the same effect we are going to want the water that leaves the sphere to be more plentiful than a single drip, so add yourself another Spawn below the Speed by Surface.

Make the settings like the ones below, instead of a trail this time we want kind of a splash off, all at once:

Then add yet another collision Spawn below the last Spawn.

And make the settings like this:

Select the ground deflector giving the dripping particles permission tosplash when they hit the ground.

8 offspring

0.0 inherited speed and leave the divergence at 12.0

Now, awhile ago we broke off of our Second Event to do this entire drip business, but now it's time to revisit our Event02 box.

See the one in the red rectangle way back up there? We need to make a new event to connect the Collision Spawn from this event, and the last one (Event06) Both of these circled blue dongles are going to come back up and connect at the event we are about to make.

This new event will be our secondary splashes after the intial ones. In order to do that we are going to have to give ourselves one more new object. Instead of just a deflector for our ground, we are going to need something visible, with a surface.

Lets create a plane that will sit right on top of our ground Deflector.

Kind of like this.

Once we have our plane which represents the visual ground like our deflector represented it's collisions, we can then go back to Particle View and drag out a new Speed By Surface into the empty stage area to the right of our Event02 box.

Like this:

Then connect both dongles to it.

Then make your settings for the new Speed By Surface event like the ones below:

Speed 15 or soVariation of 20.0

Add the new plane to the Surface Geometry list

Make the Divergence 45. so the secondary splashes move off in different directions.

Then copy your initial gravity force over below this new Speed by Surface, by again holding Shift and making it an instance of our original.

Then add another regular Collision below that, and add the Ground Deflector to it.

Make the settings for this last collision like the ones below:

Add the ground deflector

Set to collide multiple times and place the # at 2 and the Speed to Bounce.

Last but of course not least, we are going to make one last final event, drag a Delete out to the empty grey stage area above this current event like this:

And attach the last Collision to the new Event, leave the Settings for this Delete at (All)

This is our global delete for all the particles so none of them continue on forever.

If you are scrubbing back and forth and aren't seeing your raindrops do anything at all, or if you see about 12 different colors of drops, then that is because of our Displays.

Earlier when we set our first Display in the very first event 01 to Lines, and made the color white. Everytime you make a new event a new display automatically shows up with it. I have been deleting them all, if you have not been now is as good a time as any to get rid of all of them but the first one. This should clear up any multi colored tick marks all over your screen.

If like me you had been deleting them as is the case in all the images I have shared with you in this document, then you are probably not seeing your lines do anything after falling from the sky.

If we don't have a Display in every single one of our many Event0# boxes, then we have to move the display to the very top box labeled PF Source 01, in this box is only the initial one we created labeled Render 01.

Simply click and drag the one display from your Event01 box, and move it to below this Render 01, and it should take over for all events, displaying white lines for everything.

Like this:

You can add a Cache from the list underneath this Display now, and it will record the movement of all your raindrops and make it a little easier on your computer as well.

now when you scrub across your timeline, you should see your lines doing everything we spent so long setting up.

Now all you have to do is add texture, lights, a camera, and maybe a blobmesh to your particle system so there is something to render!

For a final look at our rain, go to this web address and see the finished movie.

http://animation.diclementi.com/rain.html

Hope you enjoyed this one, and I hope it didn't confuse anyone too badly! It still makes me dizzy when I do this kind of particle system. ;)

For a look at the final Particle Flow chart just in case you wish to compare with your own:

Everything feeds each other and all loops back into one another for a final symphony of raindrops!

Fun right?! 8)

This one was a rather complicated one, so if you wish to take a look at my final version of the file, you can download it here:

http://animation.diclementi.com/tutorials/Rainfall.max