Resolving three.js Raycast Issues: A Guide to Asynchronous Challenges

Uncovering the mystery behind asynchronous raycasting in `three.js` and how to ensure accurate ray origin determination for your 3D applications.
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This video is based on the question https://stackoverflow.com/q/77343629/ asked by the user 'munHunger' ( https://stackoverflow.com/u/3566441/ ) and on the answer https://stackoverflow.com/a/77344059/ provided by the user 'Mugen87' ( https://stackoverflow.com/u/5250847/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Asynchronous Raycasting in three.js

If you are a developer working with three.js for 3D graphics, you might encounter a peculiar problem where the raycast origin is incorrectly set to (0, 0, 0) after updating the camera’s properties. This issue arises when trying to determine intersections with geometry in 3D space. Let's break down this problem and explore a solution to ensure that the raycasting function behaves as expected.

The Problem

You have a piece of code that updates some properties on a three.js perspective camera, followed by a call to raycast into the scene. However, upon executing the raycast right after the camera property updates, it seems to yield an incorrect origin for the raycast.

Example Code Snippet

To illustrate the issue, consider the following JavaScript code:

[[See Video to Reveal this Text or Code Snippet]]

In your case, the raycaster's results differ significantly based on when it is called—immediately versus after a delay.

Investigating the Cause

The main issue lies within the synchronization between the camera's properties and the raycaster's calculations. Specifically, the line:

[[See Video to Reveal this Text or Code Snippet]]

overwrites the internal ray's origin. If the camera's world matrix hasn't been updated before this function call, the ray will be cast from the origin (0,0,0) instead of the correctly updated camera position.

The Solution

Step 1: Update the Camera's World Matrix

Before calling setFromCamera(), ensure that the camera's world matrix is updated with the following line of code:

[[See Video to Reveal this Text or Code Snippet]]

This will ensure that the raycaster uses the latest camera position for its ray calculations.

Step 2: Reuse the Raycaster Instance

Creating a new instance of Raycaster every time you call the cast() method can lead to unnecessary overhead. Instead, consider creating a single instance of the raycaster and reusing it throughout your application. For example:

[[See Video to Reveal this Text or Code Snippet]]

For your coordinates, maintain a single object to hold these values as well.

Refined Raycasting Snippet

Here’s an improved version of your raycasting code block:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

The quirks of asynchronous programming in three.js can be puzzling, especially when working with raycasting. By ensuring that the camera's world matrix is updated before raycasting and reusing a single raycaster instance, you can achieve accurate ray origin calculations and effective intersection checks. This not only solves the immediate problem but also enhances performance in your 3D applications.

Experiment with the adjustments discussed here and optimize your raycasting functionality in three.js!

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