In the world of animation, there's a technique known as "tweening," which involves creating intermediary steps between key frames instead of jumping directly to the final result. While there are JavaScript libraries available to handle this for you, I'll walk you through the basics of implementing tweening on your own.
Let's take an example. Imagine that when you press the left arrow key, you want to move a mesh by 1 unit along the -x axis and rotate it by -PI/2 about the +y axis. Instead of making these movements instant, consider breaking them down into smaller steps over a set duration.
For instance, if you want the animation to last for 500ms (half a second) and the browser runs at around 60 frames per second, you can divide the animation into 30 frames (since 60fps equals about 500ms). This means that for each frame, you would move the object by 1/30 units and rotate it by -PI/60. After 30 frames, the object should be close to its intended position.
However, relying solely on the browser's frame rate can lead to variations in speed. To address this issue, you can implement a real timer to handle the animation steps rather than tying them to the browser's rendering cycle.
By breaking the animation into smaller update steps (e.g., 50 steps within the 500ms duration), you can ensure a smoother and more consistent movement. This approach allows you to update the object's position by 1/50 units and rotate it by -PI/100 in each step.
let animationId = setInterval(() => {
// update position by 1/50 units
// update rotation by -PI/100
}, 10); // every 10ms
As the interval runs, it will progressively update the object, while the animation loop continues to generate new frames whenever possible.
To see this concept in action, I've provided a complete example below with support for left arrow key input:
// JavaScript code snippet
// Three.js setup for animation
// CSS code snippet
// Styles for HTML elements
<script src="https://threejs.org/build/three.min.js"></script>
While this method offers smoother animations, there may be occasional issues like skipped updates or duplicate frames. To address these concerns, you can dynamically calculate the frame rate during rendering and adjust the step sizes accordingly, although this may impact performance.
Handling Key Input for Directional Changes
With the animation and rendering processes decoupled, you'll need to introduce a flag to indicate the current action based on key inputs. The key press event will set this flag, which the update function will use to determine the appropriate action:
// JavaScript code snippet
// Handling key input and setting action flags