Creating a 2D Drawing Interface on a Plane in Three.js

To create a focused 2D drawing environment on a specific plane within your 3D scene, you can use clipping planes to hide elements before or behind your selected plane. Here's how to approach this:

Using Clipping Planes

Three.js provides a way to define clipping planes that will cut away parts of your scene. You can use this feature to create the illusion of a 2D environment by clipping everything except your target plane.

JAVASCRIPTCopied
// Define your plane based on the selected axis
const plane = new THREE.Plane(new THREE.Vector3(normalX, normalY, normalZ), distance);

// Create a renderer with clipping planes enabled
const renderer = new THREE.WebGLRenderer({ antialias: true });
renderer.localClippingEnabled = true;

// Set the clipping planes for your scene
// You'll need two planes with opposite normals to create a thin slice
const planeBack = plane.clone();
const planeFront = plane.clone();
planeFront.negate(); // Flip the normal to point in the opposite direction
planeFront.constant += 0.01; // Small offset to create a thin slice

// Apply the clipping planes to your renderer
renderer.clippingPlanes = [planeFront, planeBack];

Camera Setup

For the camera, you'll want to position it to look directly at the plane:

JAVASCRIPTCopied
// Use an OrthographicCamera for a true 2D feel
const camera = new THREE.OrthographicCamera(
    width / -2, width / 2,
    height / 2, height / -2,
    0.1, 1000
);

// Position the camera to look at the plane
// Assuming plane normal is normalized
camera.position.copy(plane.normal).multiplyScalar(10); // Some distance away
camera.lookAt(plane.normal.clone().multiplyScalar(-plane.constant));

// Adjust the up vector based on your needs
camera.up.set(0, 1, 0); // This might need adjustment based on plane orientation

Visualizing the Plane (Optional)

You might want to visualize the plane during development:

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const helper = new THREE.PlaneHelper(plane, 1, 0xffff00);
scene.add(helper);

Additional Considerations

1. You may need to transform mouse coordinates to the plane's coordinate system for drawing.
2. Consider using OrthographicCamera instead of PerspectiveCamera for a true 2D feel.
3. You might need to adjust the camera's up vector depending on the orientation of your plane.

This approach should give you a clean 2D drawing environment while maintaining your 3D scene structure. The clipping planes will effectively hide everything except the thin slice containing your drawing plane.