v0.2.1 build: releases/tag/v0.2.1
Demo video: https://youtu.be/zo6fOU6ERJ0

Lemon

Work-in-progress interactive toy. Written (mostly) from scratch, in Rust. Current top-level dependencies limited to:

• OpenGL bindings (gl_generator)
• Windowing, user input handling (glutin)
• 3D math types (cgmath)
• Rust standard library; other lightweight, de-facto-standard crates

Controls

Input	Action
Mouse Drag	Orbit camera
Mouse Scroll	Zoom camera
Mouse Click	Set camera look/follow target
Mouse Click + Drag	Grab and move lemon
Space	Reset lemon/camera position
Ctrl + Space	Create new lemon
Ctrl + Scroll	Edit lemon scale
Alt + Scroll	Edit lemon sagitta (width)
Esc	Pause/Unpause simulation
(Ctrl +) ← →	Step through physics frames while paused
Ctrl + Shift + R	Reset simulation

Toggle	Debug Visualisation
Q	Work-in-progress SDF renderer
A	Model-space transform axes
S	Torus cross-section
H	Performance histogram
Z	Lemon-Lemon collision detection constructions
X	Lemon-Floor collision detection constructions
C	Collision reaction and friction impulses
V	Linear and angular velocity vectors
B	Bounding volumes
W	Wireframes
L	Party mode

Key	Default	Modifiers	Program Setting
J	Enable	Ctrl: Disable	Histogram data logging
T	Sleep-then-spin	Ctrl: Spin only	Frame timing method

Command line options

These are all set to run on a very low-end machine; crank them up!

• -n maximum number of lemons (default: 256)
• -r [360|480|720|1080|1440|2160] (common resolutions - default: 720)
• -w custom window width -h custom window height (default: 1280x720)
• -v [true|false] (enable vsync - default: false)
• -m multisampling level (default: 2)

Current Features

• Impulse-based rigidbody physics simulation
  • Multiple bodies
  • Friction and drag models
• Analytically defined lemon model
  • 3D mesh, normals
    • Dynamic surface parametisation
  • Physical properties
    • Mass; Moment of inertia tensor
  • Collision detection procedures (with some help from numeric methods)
    • Lemon-lemon, lemon-plane collisions
    • Capsule based bounding-volumes
    • Raycasting
• Mouse-driven input
• Debugging utilities
  • Pause, step, rewind, and fast-forward functionality
  • Simple profiling histogram and API
  • Simple 3D line and pixel drawing APIs
    • Supports visualisations of complex procedures in the program
• Graphics pipeline
  • Phong shading
  • Normal mapping (deprecated)

Todo / Wishlist

• Actually nice graphics
  • Some cool art style that is tractable for me to implement
  • Procedural surface detail
    • Difficult due to UV map pinching at poles
    • Screenspace-based alternatives?
  • Other classes of citrus fruits: colour, shape, size, texture, etc.
  • Scene composition
    • Citrus tree which fruit grow and fall from
    • Fruit bowl, plates, picnic blanket, etc.
• Slicing lemons
  • Render lemon core along plane of slicing
  • Dynamic slice models
    • Mesh creation
    • Collision algorithm and physical properties
• Better physics
  • Constraint solver: currently only resolves collision pairs in a fixed order
  • Numerical integrator, especially for angular effects
    • Additionally: continuous collision detection with respect to rotation; The current implementation really struggles with narrow bodies

Sources Used

• http://chrishecker.com/Rigid_Body_Dynamics
• https://www.researchgate.net/publication/2173504
• http://realtimecollisiondetection.net
• https://www.gameenginebook.com
• https://gafferongames.com/post/collision_response_and_coulomb_friction
• https://www.sciencedirect.com/science/article/pii/S0307904X0200080X