Understanding Buffer Attribute Resizing in Three.js

The error you're encountering is related to a fundamental limitation in Three.js's implementation of WebGL buffer attributes. Let me clarify some key points about this issue:

The Limitation

The error message is quite explicit: Three.js does not support resizing buffer attributes once they've been created. This is primarily due to how Three.js manages WebGL buffers internally for performance reasons.

WebGL vs. Three.js Implementation

While WebGL does allow you to bind new buffers to attribute locations (as mentioned in the WebGL2 Attributes resource you referenced), Three.js adds an abstraction layer on top of WebGL that enforces certain constraints for performance and memory management.

Possible Solutions

Since you can't resize existing buffer attributes in Three.js, here are some approaches to consider:

1. Create a new geometry: The most straightforward approach is to create a new geometry with the desired buffer size when you need to change it.

2. Pre-allocate larger buffers: If you know the maximum size your buffer might need to grow to, you can pre-allocate a buffer of that size and only use a portion of it initially.

3. Use dynamic buffers with fixed size: Set up your buffer with dynamic: true and update portions of it without changing its size:

JAVASCRIPTCopied
const geometry = new THREE.BufferGeometry();
const positionAttribute = new THREE.BufferAttribute(new Float32Array(maxSize), 3);
positionAttribute.usage = THREE.DynamicDrawUsage;
geometry.setAttribute('position', positionAttribute);

// Later, to update:
positionAttribute.updateRange.offset = 0;
positionAttribute.updateRange.count = newDataSize;
positionAttribute.needsUpdate = true;

4. Replace the entire attribute: While you can't resize the buffer, you can replace it entirely with a new one of a different size:

JAVASCRIPTCopied
// Create a new buffer with different size
const newArray = new Float32Array(newSize);
// Copy data if needed...

// Replace the old buffer
geometry.setAttribute('position', new THREE.BufferAttribute(newArray, 3));

Regarding Pull Requests

This limitation is partly by design in Three.js for performance reasons. While it might be technically possible to implement buffer resizing, it would likely involve significant changes to the internal buffer management system and could introduce performance issues.

If you're interested in contributing a pull request, I'd recommend first discussing the idea on the Three.js GitHub repository to get feedback from the maintainers about whether such a change would be welcome and what approach might be best.

Conclusion

The most reliable approach is to either pre-allocate buffers of sufficient size or create new geometries when you need to change buffer sizes. While WebGL does allow rebinding buffers, Three.js's abstraction layer currently doesn't support dynamic resizing of buffer attributes for performance and stability reasons.

Understanding Buffer Attribute Resizing in Three.js

The error you're encountering is related to a fundamental limitation in Three.js's implementation of WebGL buffer attributes. Let me address your questions:

The Limitation

The error message indicates that Three.js doesn't support resizing buffer attributes once they've been created. This is primarily a design decision in Three.js rather than a strict WebGL limitation.

WebGL Buffer Management

In WebGL, you can indeed create new buffers and bind them to attribute locations, but this requires specific handling. WebGL itself doesn't support directly resizing buffers without creating new ones and copying data.

Potential Workarounds

1. Creating a New Geometry

The most straightforward approach is to create a new geometry with the desired buffer size:

JAVASCRIPTCopied
// Create a new geometry with the new data
const newGeometry = new THREE.BufferGeometry();
newGeometry.setAttribute('position', new THREE.BufferAttribute(newPositionArray, 3));
// Copy other attributes as needed
mesh.geometry = newGeometry;
// Dispose of the old geometry
oldGeometry.dispose();

2. Pre-allocating Larger Buffers

If you anticipate needing to resize, you can pre-allocate larger buffers than initially needed:

JAVASCRIPTCopied
// Allocate a buffer larger than initially needed
const maxVertices = 10000; // Maximum number of vertices you might need
const positions = new Float32Array(maxVertices * 3);
const positionAttribute = new THREE.BufferAttribute(positions, 3);
positionAttribute.setUsage(THREE.DynamicDrawUsage);
geometry.setAttribute('position', positionAttribute);

// Later, update only the portion you need
positionAttribute.count = actualVertexCount; // Only use this many vertices

3. Using Dynamic Buffers

For frequently changing data, set the buffer usage to dynamic:

JAVASCRIPTCopied
const attribute = new THREE.BufferAttribute(array, itemSize);
attribute.setUsage(THREE.DynamicDrawUsage);

Regarding Your Specific Approach

Trying to replace the buffer by setting:

JAVASCRIPTCopied
bufferAttribute.array = new Float32Array();
bufferAttribute.needsUpdate = true;

This won't work as expected in Three.js because the renderer keeps track of the original buffer size and doesn't support changing it. The internal WebGLAttributes class that manages these buffers enforces this restriction.

Conclusion

The limitation is partly due to WebGL's nature (which doesn't support true buffer resizing) and partly due to Three.js's implementation decisions. For now, the best approaches are:

1. Create new geometries when you need different sizes
2. Pre-allocate buffers with maximum expected size
3. Use multiple geometries with different buffer sizes as needed

A pull request to support buffer resizing would likely require significant changes to Three.js's internal buffer management system, and would need to address performance and memory management concerns.