Understanding Collisions and Physics with Babylon.js and Oimo.js

This article explores the fundamentals of collision detection, physics, and bounding boxes within the Babylon.js WebGL engine, enhanced by the Oimo.js physics engine. We'll build a demo showcasing these concepts.

Babylon.js Espilit Physics demo with Oimo.js (Replace https://www.php.cn/link/e1dd47cc816ac88ccd8100451384c97a with the actual link)

This demo, viewable in WebGL-capable browsers (like Chrome, Firefox, Safari, and Edge), lets you navigate a 3D scene using FPS-style controls. Press "s" to launch spheres, "b" for boxes, and click objects to apply impulse forces.

Key Concepts:

• Colliders Simplify Calculations: Instead of complex mesh collision detection, simpler invisible geometries (colliders) significantly reduce CPU load.
• Collision vs. Physics Engines: Babylon.js handles basic collisions (e.g., camera movement), while Oimo.js enables dynamic simulations with forces and realistic movement.
• Physics for Realism: Enabling physics and gravity in Babylon.js allows for realistic object interactions like bouncing and collisions.
• Interactive Mesh Manipulation: Picking support lets users interact with objects by clicking and applying forces.
• Debugging Tools: Babylon.js's debugging tools visualize scene elements and adjust physics parameters.

Collision Detection Explained:

Collision detection, as defined by Wikipedia, is the computational process of identifying intersections between objects. This is crucial in games and simulations. The complexity of this detection is a key consideration. Testing collisions between detailed meshes is computationally expensive, especially in JavaScript.

To manage this, we use colliders.

Colliders:

Colliders are simple, invisible geometries (like bounding boxes or spheres) that represent meshes for collision detection. This simplifies calculations, improving performance. The choice of collider (box, sphere, capsule, or mesh) depends on the mesh's shape. The Espilit demo uses bounding boxes, as illustrated below:

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This image shows a yellow deck (the mesh) and its bounding box collider.

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This shows the semitransparent red bounding boxes in the Espilit scene.

Loading the Scene:

You can load the Espilit scene using one of these methods:

1. Download from GitHub: Download the scene from the project's GitHub repository and follow the instructions in the Microsoft Virtual Academy (MVA) course (Replace with actual link) on loading .babylon scenes.
2. Visual Studio Solution: Download the pre-built Visual Studio solution.

Enabling Physics with Oimo.js:

To add physics, use the following code:

scene.enablePhysics(new BABYLON.Vector3(0, -10, 0), new BABYLON.OimoJSPlugin());

This sets gravity and specifies Oimo.js as the physics engine. Then, iterate through meshes with checkCollisions enabled but not visible, activating their physics properties:

for (var i = 1; i < scene.meshes.length; i++) {
    if (scene.meshes[i].checkCollisions && scene.meshes[i].isVisible === false) {
        scene.meshes[i].setPhysicsState(BABYLON.PhysicsEngine.BoxImpostor, { mass: 0, friction: 0.5, restitution: 0.7 });
        meshesColliderList.push(scene.meshes[i]);
    }
}

Creating Physics Objects:

The code below adds spheres and boxes with physics properties:

// ... (Material creation code) ...

function addListeners() {
    // ... (Key press event handlers) ...
}

Adding Picking Support:

To enable clicking on objects to apply forces:

canvas.addEventListener("mousedown", function (evt) {
    // ... (Picking and impulse application code) ...
});

Displaying Bounding Boxes (Debugging):

A debug UI (shown below) allows toggling collider visibility and physics properties. The code for this UI is omitted for brevity.

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Conclusion:

This tutorial provides a foundation for understanding and implementing collision detection and physics in Babylon.js using Oimo.js. The provided demo and code snippets offer practical examples. Further exploration of the Babylon.js and Oimo.js documentation is encouraged. (Include links to relevant documentation)

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