BufferGeometry dynamic attribute update strategy in Three.js r152

Dynamic Attribute Update Strategy

For attributes modified every frame in Three.js r152, set the usage hint to THREE.DynamicDrawUsage. This signals the WebGL driver that the data will be changed frequently, allowing the driver to place the buffer in memory optimized for write-heavy workloads.

Partial Buffer Updates

You cannot manually call gl.bufferSubData while relying on the Three.js renderer's internal state management without risking synchronization conflicts. Instead, Three.js provides a built-in mechanism for partial updates via the updateRange property. To update only a portion of a BufferAttribute:

1. Modify the specific elements within the attribute.array.
2. Set attribute.updateRange.offset to the starting index of the change.
3. Set attribute.updateRange.count to the number of elements to be updated.
4. Set attribute.needsUpdate = true.

When updateRange is defined, the renderer uses gl.bufferSubData internally to upload only the specified slice, reducing CPU-to-GPU bandwidth overhead.

Performance Guarantees and Assumptions

Setting usage to THREE.DynamicDrawUsage does not guarantee a specific performance gain across all platforms. WebGL usage hints are suggestions to the driver; some mobile GPU drivers ignore these hints entirely, while desktop drivers may use them to choose between system RAM and VRAM allocation.

Assumptions: This strategy assumes the total size of the BufferAttribute remains constant. Changing the length of the underlying TypedArray requires recreating the attribute and the associated GPU buffer, which is a heavy operation.

Verification

To verify that partial updates are functioning, you can use a WebGL debugger (such as Spector.js) to inspect the bufferSubData calls. You should see the upload size match your updateRange.count rather than the full length of the array.

Diagnostic Detail Needed: Are you updating a contiguous block of vertices, or are the changes scattered randomly across the buffer? (Scattered updates may render updateRange ineffective, as the range would span the entire buffer).