Fluid Solver

First steps toward building a fluid solver.

User Interface:

• Middle mouse scroll to zoom in/out
• Middle mouse click and drag to orbit the camera
• SHIFT + middle mouse click and drag to track/slide

Code Overview:

Scene Loading

Scenes are loaded by passing a path to the scene file as the first program argument. It does a simple parsing with jsoncpp to create objects.

• containerDim: size and position of the container
• particleDim: size and position of initial fluid object
• resolution: number of grid divisions on the largest axis

AntTweakBar

I've added AntTweakBar, but haven't gotten around to having it do anything yet. I also don't have a MAC so I was unable to compile the libraries for it.

Geometry

All geometry objects implement functions for collision detection. These come in a few different forms, allowing collision detection given next and previous points, given a point and distance tolerance, as well as given a point, ray, and timestep. All geometry objects also have a bounding box which at the moment is used to assist in converting the geometry to particles.

Fluid Solver

Particles are created by looping over all of the geometries' bounding boxes and checking if the point is contained within them. For solving, particles are simply accelerated by a static gravity constant and then collisions are checked against the container geometry. All information is stored in a temporary buffer which is swapped with the particle buffer at the end of the solve.

Drawing

A Painter class is used to define the drawing behavior of various elements in the scene. Each sets up their own shaders on initialization and implement methods to draw their respective objects. I found it much nicer to isolate my code this way so that I didn't have a billion gl calls in my geometry classes and a billion gl calls in my Window class. Shaders are stored as char arrays in header files. I found that the easiest way to package them with my code.

The Window sets up a glfw window and a Singleton instance of InputHandler. glfw doesn't let you have non-static callback functions so I instead have callback functions to update the state of my static InputHandler which the Window can subscribe to. From there, I can get the window/keyboard/mouse data and do the approriate camera calculations.

Parallelization:

TBB is used heavily to parallelize calculations on the particles and grid. This can be toggled on/off by defining/undefining USETBB in <core/util/flags.h>.

For the default scene, the parallelized code computes each frame in an average of 0.0494588 seconds. Without TBB, this is 0.0768101 seconds.

OpenVDB:

Currently, each frame is written out as "particles_{frame}.vdb" in the current directory

Known Problems:

There seems to be an edge indexing problem in the attribute transfer from grid to particle