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Gravity and Sink
Jean-Loïc shows you how the properties of the Gravity node work and how to set an area in which the particles will either be visible or invisible using a Sink node.
Hi, Jean-Loic Fontaine again, showing you how to use the particle system in Toon Boom Harmony 12. In the last video, I showed you how to use the Sprite Emitter and Velocity Node in order to prepare your scene for large rain fall. And it is time for us to make it move and this is with the Gravity Node. So let's see. If I enable that node, we can see that similarly, all my particles are affected by gravity. It's slowing down, but we can see the result here. If I go into setting, Gravity Node is pretty much straightforward. Trigger if it's enabled or not. Apply Gravity, obviously check is on. You can choose the gravity direction. Let's say I was to choose 1 into X Direction, you will see this updated as the gravity to go into the x-axis which is not what we want in the case. In that situation, I set up the Y Direction to -0.05 and now to by default, gravity set to either 1 or -1, but I always find it gives it way too much speed to smaller particles such as rain. So I set it to a way more smaller number which is 0.05. You could also put it in the Z Direction, and if you wanted which is not necessarily the case of rain fall, you could apply gravity between the particles to avoid collision. You could set the Relative Gravity Magnitude, Relative Gravity Epsilon, I am not sure exactly what it's doing. I think it's for the collision. The maximum distance, at what distance the particles start interacting with each other, but this is not necessary for a simple rainfall.
So with that already set, we have a pretty cool rain happening here. Note that I generate the rain behind the layer of cloud, so that way it seems to fade in the distance. But you can see now that the rain is going down like past the camera set and this could be problematic if there were camera movement or something, so I use another node called a Sink to stop the particle simulation below the camera. If I enable the Sink, you can see right now the rain drop here just disappears.
A Sink is really, really simple. It's simply an area that you can say, if you want the particle only to be generated in that area or not in that area. In that case, I set not in that area, like we can invert. And if I see the 3D Region by pressing Shift+F11, you see that I have a 3D Region here which works like a dead zone for the particle emission from above. You can move that region by applying a peg to it. So it's pretty much that for the particle generation, for the rain with gravity base. In the next video, I'll cover more a bit about the Particle Baker and a bit of the compositing required in the picture to achieve the final result.