MASTER VORONOI FRACTURING IN CINEMA 4D R18
Joseph Herman explains how to create realistic and spectacular fracturing effects using Cinema 4D R18’s new feature
Create spectacular fracturing effects with the new feature
cinema 4D R18 included a host of very important new features and one of the most significant was Voronoi Fracture. While Cinema 4D (C4D) has always been great at modelling perfect-looking objects, shattering those objects realistically into tiny pieces has traditionally been hard to do. Shatter objects realistically used to take many hours and involve a lot of tedious work. While there were third-party plug-ins available that made things a bit easier, without them it was a painstaking process to say the least.
That has all changed in R18. The new Voronoi Fracture feature not only makes it easy to break models up into hundreds (or thousands) of little pieces, but also offers lots of options to precisely control the way the fracturing takes place. Naturally, this is very useful in Vfx-heavy work involving explosions and collisions. And since the Voronoi tools are part of Mograph, C4D’S motion graphics toolkit, there are a lot of additional creative options that also make this feature extremely useful in motion graphics.
In this tutorial, I have built a scene in C4D where an aeroplane flies over a canyon and collides with the side of a rock formation, causing it to shatter into many pieces. We’ll look at how to control the fracturing of the rocks so that the smallest pieces occur at the point of impact and use C4D’S built-in Dynamics system to make the fractures react to the collision and crumble down the cliff and into the canyon. To follow along and gain extra insight, be sure to watch the accompanying video.
01 examining THE scene
Download the project folder from the online Vault, open the scene Voronoi-plane.c4d and press Play. As you can see, a plane swoops into frame and flies towards the camera. At some point, its wing collides with the rock formation on the top of the cliff, but it passes right through since fracturing has not been set up. Note that the rotation of the blade was done with Xpresso.
02 Creating a Voronoi Fracture OBJECT
Go to the Mograph menu and select Voronoi Fracture. This creates a Voronoi Fracture object in the Object Manager. Keep in mind that since it’s part of Mograph, it can be used with any Mograph Effectors. In the Attributes window, set the position of the object to X: 0 cm, Y: 777. Drag the Subdivision Surface containing the Rock Formation mesh into the Voronoi Fracture object.
03 Viewing THE Voronoi sources
The way that the rock formation will fracture is indicated by a multicoloured pattern. I want to modify it so that the fractures close to the impact will be smaller and they will get larger further away. With the Voronoi Fracture object selected, click the Sources tab in the Attributes panel. Note that there is one Distribution Source already in the list of sources. Let’s modify it.
04 Customising THE all over source
Click on the Source and change its name to All Over Source. This source will generate fractures through the whole object. Weight it so that more fractures will occur on the side of the object that gets hit by the plane. Change the Distribution Type to Exponential and turn the X- and Y-axis Affection off and set the Z-axis Affection to the right. Set the Standard Deviation to 0.07 and the Point Amount to 175. I used a Seed of 12347, but you can experiment with different values. Now more pieces will occur on the right side than the left.
05 Creating THE impact source
Create a second distribution source to make smaller fragments at the wing’s point of impact. Click on the Add Distribution Source button and rename the new source Impact Source. Change the Point Amount to 300. Next, twirl down the Transformation controls and set the Y and Z scale to .025 and the Z position to 255 in order to move the generator to the area where the wing hits the rock. Feel free to further modify its position as you see fit.
06 setting up rigid Body Dynamics
I use C4D’S Dynamics to simulate the impact and crumbling of the fragments. Right-click on the Voronoi Fracture object and choose Rigid Body from the Simulation Tags submenu. With the tag selected, in the Attributes panel,under the Dynamics tab, change the Trigger to On Collision. In the Collision tab, set the Inherit tag to Apply Tag to Children and Individual Elements to All. Set the Bounce to 10% and the Friction to 95%.
07 setting up Colliders
For the plane to collide into the rock formation, we need to tell C4D’S dynamics system that it is a collider. Right-click on the Planebody Mesh and choose Collider Body from the Simulation Tags submenu. Also, add Collider Body tags to the cliff and the boulder so that they interact with the pieces as they crumble and fall, and set their Bounce to 10% and Friction to 95% as well.
08 Fixing Dynamics Triggers
Sometimes there are some fragments that remain static. To fix this problem, set a keyframe to change the Trigger of the Rigid Body simulation to ‘Immediately’ right after the plane hits the rocks. First, select the Rigid Body tag on the Voronoi object, go to frame 51 where the plane hits the rocks and in the Collision tab, set the first keyframe for the trigger (to On Collision). Advance one frame after the plane clears the rocks, change the trigger to Immediately and set another keyframe. Any static fragments will now fall.
09 setting up materials
You can generate selection tags for the inside and outside surfaces of fractures, allowing you to define different materials for them. To do so, click the Voronoi Fracture object and in the Selections tab, tick Inside Faces and Outside Faces. Note that polygon selections (to the right of the Voronoi Fracture object) get made and can be used on two separate materials (for the inside and outside). I simply created two clay coloured materials, one for the outside surface and a slightly darker one for the inside surfaces.
10 Caching THE Dynamics
When using Dynamics, you should cache (or bake them) before rendering. This allows you to quickly scrub back and forth through the timeline more accurately. Click on the Rigid Body Dynamics tag and in the Attributes panel in the Cache tab, click the Bake All button. Notice that the simulation is now snappier and more easily viewable when scrubbing the timeline. 11 Finishing up
Congratulations! You have used Voronoi Fracture to shatter a rock formation after it has been hit by the wing of a plane, causing it to collapse into a pile of rubble and tumble down the side of a cliff. I have left the final lighting and rendering up to you and your renderer of choice (I used Octane). For more information about Voronoi Fracture, watch the accompanying video.