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We used multiple Perlin noise textures and interpolated their product with a standard u-v texture. We then took Gaussian Blob samples to simulate the features of fire. Lastly, we applied a color gradient to give an orange color to the blob.
Rendering Result
Visualization of the simulation and rendering pipeline.
We decided to use 3D textures to hold our different attributes that describe a fire. In our simulation, we calculated the corresponding values for velocity, pressure, and temperature for voxels of fire molecules.
Here is the formula that we used:
In the formula, u is the velocity, p is the pressure, ρ is the density of the molecule mass, and f is the external force on molecules. The first term represents the advection, which is the velocity of a fluid that causes the fluid to transport objects, densities, and other quantities along with the flow. The term inside the parenthesis is the divergence, which represents the rate at which density exits the region.
The second term simulates how pressure gathers and generates force and provide accelerations to the surrounding molecules.
When time advanced, we computed the advection and divergence based. Based on the interaction between neighboring molecules, we propagated the changes in temperature, pressure, and velocity correspondingly. We then updated the values in each 3D texture and rendered the resulting molecules to the screen with Unity.
The green color represents the propogation of velocity.
The main difficulty of our implementation came from debugging the propagation of the attributes across timestamps. Unity is not designed to accommodate print debugging so we created a script in Python to calculate the values for a 2D fire simulation. It turned out that the values propagated as expected, which proved that our formula was correctly implemented. We then created a debugging shader to fill in empty textures so that we could see how the values advanced in our model.
In the next stage, we would like to complete the implementation of our simulation and rendering engine. We would introduce the vorticity constraint, which preserves the curling behavior of the fire. Additionally, we will simulate and render fuel level and smoke to make the fire look more realistic. Finally, we also expect to generate a GIF or a real-time application to render the simulations and incorporate some environmental objects in our rendering.
https://docs.google.com/presentation/d/1p8Mq5FJ8h6zP2ontchP7ci2boV2jzp6p15G_GkCUlQo/edit?usp=sharing
https://www.youtube.com/watch?v=jdkjiDlUR0A&feature=youtu.be
- “Real-Time Simulation and Rendering of 3D Fluids”, Keenan Crane, Ignacio Llamas, Sarah Tariq https://www.cs.cmu.edu/~kmcrane/Projects/GPUFluid/paper.pdf
- “GPU Gems - Chapter 38. Fast Fluid Dynamics Simulation on the GPU”, Mark J. Harris, University of North Carolina at Chapel Hill, https://developer.download.nvidia.com/books/HTML/gpugems/gpugems_ch38.html
- “Smoke Simulator”, Rachel Bhadra, Jonathan Ngan, Kenneth Tsai, https://rachelbhadra.github.io/smoke_simulator/index.html