Production Process Outline
In this outline I would like to detail the steps I went through to complete this shot with a focus on the important role Fracture played in the process. First and foremost, I would like to address the fact that without Fracture I can't imagine how I would have created this shot without breaking each piece with the split polygon tool by hand. No one wants to do that.
-Production and Shooting-
I knew early on that texture issues with Fracture were at the bottom of the list of things to fix in development. I also knew that what I would be shooting would most likely have to be the texture for the actual fragments as well. So I shot a simple piece of footage behind the building I live in.
I used Boujou to track the shot. I won't go into the specifics of settings and what not but I was able to pull a track from the footage.
-Fracture and Scene Setup-
Once I had all the pieces to begin it was time to start using Fracture. I knew I wanted to create a similar effect to the one I had with the burrowing where an object could break only a specific area while leaving another larger shard unaffected. To create the broken shards I used a brick map I made by taking a photo of some bricks and desaturating them and adjusting the brightness and contrast values until I had something that I could use.
Even though I saw in several demonstrations you could paint another crack map and add additional complexity to the brick cracking I then ran into a problem where, for some reason, it just wasn't creating the pieces I wanted. Plus, it seemed like it was taking longer to calculate due to the complexity. So I just painted the cracks I wanted right on the brick map itself. That gave me the breaks I was looking for.
-Simulation and Breaking-
The simulation phase took a lot of tweaking and tricks but, such is the life of the effects artist. Effects are all about faking phenomena and explosions. So to create the idea of the explosion blowing out the wall I used a sphere hitting the wall. Now I knew I couldn't key frame the sphere so I decided to key frame the attributes of the simulator to get what I needed. I key-framed the gravity so that the ball would be falling towards the wall and after a few frames I key-framed it back in the -Y direction of 9.8. In my thread Kevin Mannens suggested that I increase this value because the shards were too floaty so in the end that value changed to 19 or 20. I also increased the initial velocity of the sphere to make the impact hit harder. The process took a lot of simulating and tweaking to make this work..
Animated from these values to -20 on the Y axis. The only reason these values were set like this because my scene was at an angle because of the Boujou data.
These values are set like this for the same reason the gravity was adjusted the way it was.
I also created some simple geometry that resembled the wall, the window frame, and the glass to be broken. Even though you may not see the glass I feel it's important to add it.
-Filters and Collision Events-
I have to say that when I first picked up Fracture it wasn't very intuitive, but I don't know many things that are. Obviously, the biggest hurdle was understanding the collision events and filters. I ran into several issues where the window frame wasn't breaking but that was because I was thinking about collision events all wrong. Once I understood them a little better, they made a lot of sense. This experience is to be expected when there are so many different ways to approach the same effect. I went with two events with simple filters. The first event was that of the ball hitting the wall. This event looked something like this:
The next step was to create an event for the window frame and the glass. I wanted the broken pieces of the wall to initiate the the fracture. I used the “first or second” filter attribute so that I would not be defining any specific thing as first or second.
This setup would also make the window and glass break at the same time but because of the speed at which this was all happening it would not be noticeable. I'm sure there are several ways to approach this problem but this is something I like abut Fracture. Any number of people and artists can come up with multiple ways to achieve the same effect. The downside is that a person could also over complicate a simulation by adding more filters and events than are necessary.
Once I had the simulation in a playblast looking how I wanted, it was time to start planning the movement of the simulation to a platform where I could work on it with any computer. So that meant baking the simulation to key frames. Now this is something I really like about Fracture. I am able to bake the simulation to keys and keep this work-file for tweaking later. So once I had it where I wanted I replaced the simulation with keys. Now this is the permanent kind of thing so I had another work-file I used for this. This feature is also great because when Kevin Mannens suggested I increase the gravity I was able to easily go back to that file and make the adjustment. Then I just saved that as another scene and imported it into my most current work-file.
Of course with an explosion you are going to have some fluid simulations. So, using the key framed pieces of fractured geometry, I created some motion fields and collisions to help make the simulation more turbulent. I also used a few volume axis fields but I won't go into great depth as to how I set up the fluid system because that would take forever. The important thing is how the fractured pieces gave me more detail in the simulation.
I also added some other smaller pieces of debris using an nParticle setup. Using some fractured pieces of bricks as my emitters I was able to create some extra debris. I also used Fracture to create the instanced pieces of geometry.
On top of everything I have mentioned thus far I also added a few other things in compositing and in Maya. These are images and descriptions of all the layers in the rendering and compositing phase.
Hole In Wall
I created a room behind the hole. This was done with some simple textures of my apartment and a cube. I placed an area light in the back of the room and wrote a simple noise expression to create a flame like flicker to enhance the fire element to be added later.
Fractured Objects and Debris
This is the fractured geometry after render. I used an image of frame 75 in the footage projected from a duplicated Boujou cam that is frozen at frame 75. Frame 75 was the highest point of this camera move so I used it as it had the most building texture info. I then projected this image on all of the pieces and created a texture reference object for all of the pieces. I used a while loop to accomplish this.
I also painted some black burned areas on that frame in Photoshop to enhance the blown out affected area. This also projected those burned areas onto the bricks.
Now I know I took the easy route on this one by using footage of fire on a plane but this is how some things are done. I could have made a fire sim but for the sake of time you sometimes make compromises and this was one of those times.
Fluid, Dust and Small Debris
These are the layers of fluid, dust, and debris. I added the dust later by using another nParticle sim and creating some very fine dust. Yet another small effect but I feel it enhances the overall look.
-Color Correction and Grading-
Of course I then color corrected the pieces to match better. I used the grading I did because the whole explosion thing reminded me of “Children of Men”and it had this desaturated cold tone to it.
As a note I would like to state that I began work on the actual shot January 20th 2010. I completed the shot on February 10 2010. This does not mean I spent 8 hours a day working on the shot. That being said I will break the time-line down in a rough estimate of hours spent working on the shot. The hours below also reflect the time only spent in Maya. It also includes simulation time which would vary, computer to computer. It does not account for pre production.
Hours 0 – 4
This time was spent setting up the scene in Maya and running initial sims. The sims included pre crack map sims. Just simple voronoi paint/localized tests. Most of this time was in simming and waiting.
Hours 5 – 10
This time was spent adding the crack map and breaking up the other pieces such as the window frame and glass. A large part of this time was also spent simulating. Playing with the key framed gravity and initial velocity values as well as adjusting the collision events.
Hours 11 – 13
I spent a couple of hours here adjusting the simulation and baking the sim to keys. Once the keys were baked and replaced I moved them down the time line to where I wanted the explosion to happen.
Hours 14 – 18
This time was spent creating the the fluid system. I only had a few minutes here and there to put this together. I was super busy at work so any free time I had went to tweaking this.
Hours 19 – 21
This time was spent setting up the particle systems.
Hours 22 – 24
This time was spent setting up render layers and comping. I had a test comp ready to go while I waited for the renders.
As I may not have mentioned this before I will now. Fracture even in it's infancy is a very powerful tool. Albeit the final look is the result of a lot of additional effects, I would not have tackled a shot like this in Maya if it were not for Fracture. Fracture offered me a procedural destruction solution right in Maya plus it has it's own physics simulator. There are some scripts out there to break things up but sometimes you don't want just a voronoi method. You might want bricks or you might want to split an object in specific areas. This is where Fracture really shines. The plethora of options for breaking up geometry. I can not remember the last time it was so easy to break something in Maya. Additionally, I like that, if need be, I only need one license of fracture per artist. Once you have the simulation you can bake it to keys and replace with keys and then you have a scene that's ready for network rendering and so forth. I also like the event color system. I used it quite a bit on this project to make sure the things that were breaking were doing so when I wanted them to.