zig-animate

A property animation library in Zig.

Demo 1: Property Interpolation

Full demo code in animator.zig.

const start = Vec2{ .x = 0, .y = 0 };
const end = Vec2{ .x = 1, .y = 1 };

const anim = Animator(Vec2).init(start, end, EaseInCubicVec2);

// 2D Cubic Easing
try std.testing.expectEqual(Vec2{ .x = 0.015625, .y = 0.015625 }, anim.eval(0.25));
try std.testing.expectEqual(Vec2{ .x = 0.125, .y = 0.125 }, anim.eval(0.5));
try std.testing.expectEqual(Vec2{ .x = 0.421875, .y = 0.421875 }, anim.eval(0.75));
try std.testing.expectEqual(Vec2{ .x = 1, .y = 1 }, anim.eval(1));

Demo 2: Sequencing

Full demo code in sequencer.zig.

We can animate a complex object:

const TestObject = struct {
    value: f32,
    other_value: Vec2,

    const Self = @This();

    fn update(self: *Self, value: f32) void { ... }
    fn update_other(self: *Self, other_value: Vec2) void { ... }
}

Sequencing multiple property animations:

var testObj: TestObject = undefined;
testObj.value = 30;
testObj.other_value = Vec2{ .x = 10, .y = 10 };

// Go from 30 to 50 over 80 frames
const valueAnim = animator.Animator(f32).init(30, 50, curves.EaseInCubic);
const valueEvent = Event.create_transition(TestObject, f32, &testObj, &valueAnim, 80, TestObject.update);

// Go from (10, 10) to (6, 4) over 65 frames
const otherValueAnim = animator.Animator(Vec2).init(Vec2{ .x = 10, .y = 10 }, Vec2{ .x = 6, .y = 4 }, EaseInCubicVec2);
const otherValueEvent = Event.create_transition(TestObject, Vec2, &testObj, &otherValueAnim, 65, TestObject.update_other);

// Create a sequencer
var sequencer = Sequencer.init(TestAllocator);
sequencer.add_event(0, valueEvent);
sequencer.add_event(0, otherValueEvent);

// Move the sequencer forward
sequencer.tick(10);

// Check the values
const expectedVal = curves.EaseInCubic(30, 50, 10.0 / 80.0);
try std.testing.expectEqual(expectedVal, testObj.value);

const expectedVector = EaseInCubicVec2(Vec2{ .x = 10, .y = 10 }, Vec2{ .x = 6, .y = 4 }, 10.0 / 65.0);
try std.testing.expectEqual(expectedVector, testObj.other_value);

Key Concepts

The three files in this library are:

• animator.zig: Contains Animators, which are objects that animate over a given property. You have one animator per property, so a location/rotation/scale animation might have locationAnim: Animator(Vec3), rotationAnim: Animator(Quat), scaleAnim: Animator(Vec3) (respectively).
• sequencer.zig: Allows for Actions (one-off event) and Transitions (ongoing event) to be scheduled and run. You have one sequencer per project/module/grouping of animations.
• curves.zig: A collection of interpolation functions for f32. See the animator.zig class for an easy example of how to create higher dimension interpolation functions (e.g. for Vector2/3/4/etc).

Examples

In each source file, there are fully-commented tests demonstrating some key patterns.

For example, see sequencer.zig.

Building

Standard Zig library:

zig build
zig build test --summary all

About

This repo is a mirror of the in-tree animation library from my personal game engine project. As such, this library is actively (albeit infrequently) maintained.

Contributions

Contributions are welcome, although keep in mind the library scope is intentionally small.

Licence

MIT Licensed - do what you want!