VSFX 728 - Wildfire
① Week6 - Reference
For the last project, I wanted to experiment more with pyro in Houdin, so I chose three reference videos. In the end, I chose the second one - Forest Fire, because the visualization of the smoke and flames in this reference video is very striking!
② Week 7 - Environment & Pyro Test
1. Environment - forest
Render: Redshift
Houdini Version: 19.5.640 – py3.7
Light: One Domelight
Tree model resource: https://www.cgtrader.com/free-3d-models/plant/conifer/2021-pbr-incense-cedar-collection-calocedrus-decurrens
For the environment part, I mainly use instance and nodes of mountain, scatter, maskfromgeometry as well as attribrandomize (pscale and N). Please slide the image below to view the process.
2. Pyro-flame simulation (instance & copy to point)
Since the reference video is a forest fire and not a single fire, there will be many sources of fire, therefore I tried two main ways, first is the pyro instance, and second is copy to point. After testing the two ways, I decided to use the former instance way, because this way is more helpful to optimize the memory usage and speed up the rendering time.
Pyro instance
Basic Pyro instance guide: https://www.sidefx.com/docs/houdini/pyro/pyroinstancing.html
Pyro Copytopoint
3. Troubleshooting - Pyro instance
Since my terrain is not a flat surface, after testing the Pyro instance for the first time, I found that Pyro just ended up Y0, and it does not fit with my terrain scatter point position. The simple way to solve this problem is to click the Treat Y as “Open” (Pyrosolver - Bounds - Boundary Conditions).
③ Week 8 - Smoke & Fire & shading
1. Flame render and simulation
During this weekend, I started working with the shape and shading of the fire and mainly created three different shapes of fire source. For the shading, because I’m using Redshift in Houdini for rendering when I try to assign the volume rs material, the flame does not shows up. then I followed a tutorial from YouTube (by Resilient Picture Company), which is to create an RS volume in the shop and assign it to the material part.
2. smoke simulation
First simulation test - smoke
After the first smoke simulation test, I carefully compared the reference video and I realized that the smoke at the very front of the video was a subtly rotating smoke shape. This is very different from the test of mine.
In this approach, I mainly followed the tutorial (courtesy of Theory Accelerated) to create a custom velocity field in volumevop and simulate the motion of the smoke torsion based on the shape of the helix. However, after applying pyro smoke, and adjusting various atrribute, I get results that are very different from the reference video, and I can't achieve the twisting effect in the reference video.
Theory Accelerated )
For this time, I have try volumndeform and bend node (twist section) to make the whole smoke have a twist shape. But because the amount of smoke in my reference video is large and at least two distorted rotations are visible. After I tried it, I realized that too much rotation would cause some details inside the smoke to be distorted.
After I went through a few different ways, I tried giving Helix a rotating animation and then applying Pyro afterward, and the result I got was pretty close to the reference video. Please slide the image below to view the process.
④ Week9 - Smoke & Look Dev
For this week, I start working with background smoke and look dev.
1. Background smoke
Except for the rotating smoke at the front, I mostly used copy to point to simulate the smoke in the background. For the more distant smoke, I used a simple sphere and a sparse billowy smoke to simulate the smoke.
2. Look Dev - Lighting
Regarding the lighting, I started with one domelight, but after comparing it to the reference video I realized that the lighting was too different, and the smoke in the reference video had a warm/cold contrast difference, so I mainly replaced the HDRI and added distant lights, spot lights and area lights for the sides of the smoke.
Render: Redshift
HDRI link: https://polyhaven.com/a/air_museum_playground
After comparing the reference video over and over again, I found a lot of changes that need to be made, for example, the proportional size of the tree needs to be smaller and it should be denser, while the color of the smoke should be more bluish with a darker brown.
⑤ Week 10 - Rendering
Due to the large size of the file cache (about 500GB for all the pyro simulations together) and the fact that the render farm was very crowded during the end of the quarter, there wasn't enough time to render all the smoke effects, so for the rendered video at this stage I removed the background smoke, some lighting and kept only the predominantly flaming and rotating smoke (also change the division scale), as well as lowering the resolution (960*540).
Over the summer I plan to reorganize the files and render a high-resolution version with all the smoke effects intact.
Yilin Zhao / Vsfx728 / Houdini / Wildfire