Döhrener Tower Project

For the final project of the VSFX 728 class, I decided to tackle something that involved somewhat large destruction, since, I need to challenge myself, and It’s something that I’d like to have on my reel and I’d learn a lot from it. 

One of the main goals was to have something with different layers of materials, for example, glass, wood, bricks, and such. Instead of just breaking a big chunk of a one material wall or something like that.

Browsing online for inspiration and reference I stumbled upon a medieval watchtower in Hannover, Germany, the Döhrener Tower. A building from the 14th century that looks really interesting, and pretty and has enough detail that would work and look pretty if destroyed.

I started this project by blocking out the overall proportions of the tower in Houdini. I tried to aproximate the measurements by using the door as reference, as well as the top living area to get a sense of how tall it was. Paul and Luiz for scale reference 😁.

Then, I started to model the hero tower. I separated the tower into three main sections:

  1. The roof with all the tiles
  2. The main body or living area
  3. The tubular base

For the roof, I extended the chimney to the interior, in hopes of making it have some more interior detail and realism. Hopefully this will enrich the overall destruction, once the simulation is actually run. 

If you look carefully at the image, you can see that the tiles still need some work to get rid of problematic interpenetrations, which is something that I will have to address with great care. This to make sure Bullet takes the pieces and they don’t explode.

The main body was very straightforward with me modeling one of the faces and then having them revolve around the general octagon shape of that part of the tower.

And finally, the base. I did a brick, gave it some curveness and rotated it around and made vertical copies, then used boolean to generate the mortar in between. The last steps were to boolean some of the windows and add the wooden door.
Here’s a final look of all the elements together:

Pre-Fracturing Process

After finishing the tower model, I took each section and fed its components through custom for each loops to fracture the pieces. Through this method I could customize and have more control over the shape and amount of pieces each component would generate.

Once the pieces were made, a custom name was assigned to each of them. The unique names are critical later on when constraining the geometry in the simulation.

Constraint Setup

Through the use of a Connect Adjacent Pieces SOP, contraints were created per section of the tower (roof, body and base). These individual elements were assigned an integer attribute prior and was used on a separete connect Connect Adjacent Pieces SOP to connect the 3 sections of constraints.

Through the use of Primitive Wrangles, I manipulated and customized the strength of the constraints to achieve a more organic breakage. And to generate chunks of geometry through clustering and debilitating the constraints between clusters.
My intention was to have the tower be destroyed by catapult balls. Originally I tested having the balls be RBD objects interacting with the tower, but it proved really difficult to control and art direct. So instead I did a simple RBD simulation where I have 3 balls being launched into the air and falling right where the tower would be. I cached this and used them as passive colliders instead. Through this way I could have them destroy the tower without worrying too much about the interaction.

With the tower and colliding objects cached and ready, I put in place the main RBD simulation. The setup is pretty straight forward: An RBD Packed Object for the tower, connected to a Rigid Body Solver and a Constraint Network with Gle Constraints. 

The only addition to the setup was a Geometry Solver in which I had two wrangles to manipulate the constraint geometry. In the first one I break a section of the tower after a certain frame. In many of my tests the colliders didn’t debilitate it enough to make it fall, so it was easier to do this to guarantee it falling down. In the second, I debilitate the cluster to cluster constraints to guarantee a chunky destruction while it falls.

After many, many oh, so many tests, I locked the simulation and cached it out. From that cache I used a Debris Source SOP to generate points from the breakage of the tower. 

From these points, I made a POP simulation in which the points would inherit the velocity and color of the piece of the tower from where they were originally generated.

I converted these points to a fog VDB to pass them as dust. In this step the color is lost. To get it back, a second VDB is created through a Volume Rasterize Attributes SOP in which I rasterize Cd to a volume. This new VDB is then combined with the fog and through the shader, it gives the fog its intended color. 

The last element added was a Pyro simulation sourced from the oirignal Debris Source. This complimented the look providing the simulation with a thicker and heavier looking layer of dust.
With all the layered simulations in place it was time to put the caches together and submit to render.

Rendered Result

There are many aspects of this project that I’d like to be able to tweak in the near future to improve upon the overall architecture of the tower as well as to fix erros here and there in the simulations. And Finally, I would like to haver a better defined dust simulations, but unfortunately I ran out of time and the deadline came too soon. 

Even though I panicked a lot during this project, I learned a lot from doing this and feel partially satisfied with the current result.

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