With the TwoDPhysics Addon we can add physics to grease pencil objects. This makes it easier to to animate when gravity and collisions are involved; instead of drawing every frame we just run the simulation. Additionally you can use constraints, meaning the GP objects are not just falling down or colliding. For example: Pivot Joint, Groove Joint, Damped Spring, etc.
Although SreeRaj (the developer) provided quite some video’s, I give you here a quick start guide so you get an idea where the addon is coming from.
How the TwoDPhysics Addon Works
First a few things to keep in mind in order to understand the working of the addon:
By default the gravity is -y in this addon. This is because we are now working in 2D space, on the XY-plane. So that is the top view.
There are settings to find in the Properties panel. One place is the Scene Properties, and the other is the Physics Properties. The scene properties are global settings, like settings for the 2D physics world. And in the Physics tab you find settings for each greasepencil object.
The idea is that you paint/create a greasepencil object, but on top of that you define a shape object (could be curves) for the Physics Engine. Called collision shape. The collision shape will be parented to the greasepencil object and won’t show up in the render.
Each time you change a rigid body, you need to bake the simulation (Properties Panel > Scene properties).
Press 5, then 1 on the numeric keyboard (Mouse cursor needs to be in the 3D viewport). This bring the 3D viewport in top view.
Create a collection and call it for example: 2Dworld
Enable 2D physics in the properties panel > Scene properties > 2D Physics world > Create 2D space.
Click on World Settings that appears, and click on Enable Visualisations. So you can see the collision objects.
Under World Collection you fill in the collection you just made. In my case it’s collection 2Dworld.
That’s it for the setup.
Create a grease pencil object (Shift+A, G, B), go in draw mode and create a line (the floor, or terrain). Best is to mind the origin; so draw through the origin and not far away from it. Otherwise the collision shape later won’t match and then you have to go in edit mode to match it.
Go in object mode and go to the properties panel > 2D physics object > Create 2D object.
For a floor choose Static.
You see a collision shape (Circle) in the 3D viewport, which is for the physics engine to calculate physics.
We need to change the shape because our floor is not really a circle but more a line.
So, you click on the words: Collision Shape at the bottom and properties will appear.
Click on Poly, and make create/add a curve object. A path object is handy in this case.
Go in Edit mode to line it up with the floor.
Select the grease pencil floor and in the settings for Collision Shape > From Curve you give in the Path object you just created.
We’re almost there
So we have a static object now. Next is to create another greasepencil object (above the floor) and do the same. But the difference is that we make a Dynamic object. Start with a simple object like a ball, or some primitives. Once finished with creating objects, you go to Properties Panel > Scene Properties > Bake 2D Physics. Run the time line and see the animation.
That should getting you started with the TwoDPhysics Addon