Realtime Lift and Drag

Christian Eckhart, William Newey, Austin Quick, Sebastian Seibert

General Code Info

• Uses the c++17 standard for constexpr if, structured bindings, string_view, and more

• Non-local variables are given a prefix

Prefix	Usage	Example
m_	non-public member variables	class Foo { int m_bar; };
s_	static variables	static float s_lastTime;
k_	constants	static const int k_maxSize = 400;
g_	global variables	extern string g_usedInfrequently;
u_	shader uniforms	uniform vec3 u_color;
i_	shader invocation variables	vec3 i_totalLift;

• #defines should only be used when absolutely necessary. Use constant variables to preserve type and code sense

• Source code is organized by project into src and include directories. src should contain any code that is not to be used by other projects. include should contain a directory with the same name as the project, which contains any headers to be used by other projects

• Resources, such as shaders, meshes, images, etc. are kept in the resources directory and are organized by project

Project Overviews

Common

Common is a static library and serves as a catch-all project for any more "general purpose" code that is used accross multiple projects. All other projects use it. This project contains the Global.hpp header, included nearly everywhere, which contains some absolutely fundamental typedefs and includes.

RLD

RLD (Realtime Lift and Drag) is a static library and contains the actual meat and potatoes of the repository, even if it currently has only one header and one source file. It contains the functions for simulating lift and drag on a model given a bunch of variables. It is designed like a public interface, such that it can be easily be used by other projects and depends only on the Common project.

UI

UI (User Interface) is a static library designed to meet the GUI and user input needs of the repo. It follows a typical object-oriented Component class heirarchy, and contains classes for text, text fields, graphs, texture viewers, and groups to organize all these. To be honest, it's a little half-baked. It provides only the functionality that was necessary at the time - it has no buttons or sliders - and it's probably not the best designed. However, it works, and is infinitely better than a million hard-defined constants and pages of reused rendering code.

Visualizer

Visualizer is an executable for visualizing the realtime lift and drag simulation at work. It features a front and side view of the model in its current simulation state. The simulation can be stepped through one slice at a time, or whole sweeps at once. Additionally, it shows curves of the lift, drag, and torq values per slice and per angle of attack. Visualizer uses the Common, RLD, and UI projects.

Controls

• space to step to the next slice
• shift-space to do a whole sweep, or finish the current one
• ctrl-space to toggle angle of attack auto progression. When sweeping, will automatically progress to the next angle of attack
• up or down to increment or decrement the angle of attack and perform a sweep
• right or left to increase or decrease the angle of attack and perform a sweep once released
• o and i to increase or decrease the rudder angle
• k and j to increase or decrase the elevator angle
• m and n to increase or decrease the aileron angle
• The graphs can be manipulated
  • drag to move the curves
  • scroll to zoom in or out
  • shift-scroll to zoom the range only
  • ctrl-scroll to zoom the domain only
  • = to reset
• The texture viewers can be manipulated
  • drag to move the texture
  • scroll to zoom in or out
  • = to reset
• The model viewer can be manipulated
  • drag to rotate the camera around the origin
  • scroll to zoom in or out
• Many of the variable texts can be edited by clicking the value, typing whatever, and then pressing enter

FlightSim

FlightSim is an executable and a basic flight simulator using the RLD technology. Uses the Common, RLD, and UI projects.

Controls

• w or s to pitch up or down
• a or d to yaw left or right
• q or e to roll left or right
• space to thrust
• k to toggle wind-view
• shift when in wind-view to view orthographically
• r to reset the simulation
• p to pause the simulation
• drag to rotate the camera
• esc to exit

ClothSim

ClothSim is an executable and cloth simulator using the RLD technology. Primarily set up for simulating a jib sail, but can be set up to simulate a flag or any other cloth object. Features option to see forces on each cloth vertex, or visualize the cloth vertex constraints. Additionally shows the front RLD texture. Uses the Common, RLD, and UI projects.

Controls

• drag to rotate the camera
• scroll to zoom in or out
• left or right to rotate the sail CCW or CW
• up or down to extend or retract the clew
• right-click to "blow" on sail
• z to disable rld simulation
• x to do one sweep per frame
• c to do one slice per frame
• space to step one slice
• The texture viewer can be manipulated
  • drag to move the texture
  • scroll to zoom in or out

The cloth simulation is done via a basic varlet integration approach in a similar manner as described in this article. There are two key differences however. First, the data is stored on the GPU and the algorithm is performed in parallel using OpenGL. Second, while the approach in the article is tailored specifically for rectangular cloth, we support cloth of any shape, so long as appropriate constraints can be provided. Although lacking self-collision functionality, the result is performant and otherwise realistic.