What is this?

Two things:

1. A collection of tools for doing cool animation stuff in DragonRuby
2. A DragonRuby-based GUI for quick prototyping with said tools

How do I use it?

If you only need the tools, clone this and copy whatever files you need from lib into your game.

The GUI is available in your browser and as a download on Itch.io.

Alternatively, you can run the GUI using this repo. Get a fresh copy of DragonRuby, delete the mygame directory and clone this repo as the new mygame. Then run the game.

The tools

Bezier.ease

Create a cubic bezier easing function, suitable for using with DragonRuby's built-in Easing.ease method.

Note that DragonRuby has a built-in cubic bezier function, but it is only useful for computing a traditional 2-dimensional bezier curve (input t to get (x, y)). Bezier.ease produces a 1-dimensional bezier curve (input x to get y) which is what you want for an easing function. See here for more explanation of the difference between these kinds of curves.

This works the same as your web browser's cubic-bezier CSS function, so any resources about that function (such as cubic-bezier.com) apply to this as well!

Enum Utils

Functions for managing keyframe animations using Ruby's Enumerator. In a nutshell, these let you create animation objects that automatically manage animation state independently of the tick method.

• ecount for encapsulating a tick-based animation where you only need the number of ticks since the animation started
• eease for encapsulating an easing-based animation where you get the progress of the animation as a number from 0 to 1. Takes an easing functions (such as those produced by Bezier.ease) to tweak the "feel" of the animation
• Enumerator::Yielder.run for composing individual animations into larger ones
• create_easing_func for creating easing functions in a way similar to DragonRuby's built-in ease, but with unconstrained output so that your functions can anticipate/overshoot during the animation
• Numeric#lerp for doing a linear interpolation between two numbers. Handy to call on the output of an easing function

See my blog post for more details.

Second Order Dynamics

SecOrdDyn is a class that encapsulates a second-order dynamic system. In English, it lets you add physical properties (springiness, momentum, etc.) to any 2-dimensional input (such as position).

For example, say a sprite's position is unpredictable (dependent on user input or randomness). Then you can't use easing functions to tweak its movement because you don't know where it will be in the future. But you can create a SecOrdDyn and feed it a desired position each frame, then the system will output an actual position to use for the sprite, and you can tweak the "feel" of the movement simply by modifying the parameters of the system.

See this video for more info.

Vector Math 2D

A slight modification of https://github.com/xenobrain/ruby_vectormath, used to make the second-order system updated free of memory allocations.

Clipboard

Allows you to copy/paste strings from the system clipboard. Works on Mac, Windows, and Linux (if you have the right packages installed).

Totally unrelated to animation but I needed it for the GUI, so here it is.

The GUI

Running main.rb in DragonRuby lets you play around with Bezier.ease and SecOrdDyn. Since these two components are all about achieving the right "feel", they are very hard to use if you're only looking at the numbers.

The two UIs (selected with B/D) let you tweak the parameters, see a preview, and finally Ctrl-C to copy the code for reproducing that feel in your game!