WebGPURenderer: Add ReadbackBuffer as parameter

[sunag]

Fixes #33281

Description

Add ReadbackBuffer as a parameter; this should help share the GPU buffer between attributes.

Function signature

Single function signature.

async getArrayBufferAsync( attribute, readbackBuffer, offset, size ) : ArrayBuffer

Simple usage

The same readback buffer will be used for all subsequent requests if you use the simple method await renderer.getArrayBufferAsync(attribute); you can use attribute.dispose() to discard the readback buffer.

const arrayBuffer = await renderer.getArrayBufferAsync( attribute );

Obtain multiple data from the same readback asynchronously

To obtain fractions of the same buffer in parallel, it will be necessary to use instances of ReadbackBuffer. If the dev does not use them, they will receive an alert with instructions.

// start

let buffer1, buffer2;

buffer1 = new THREE.ReadbackBuffer( 8 );
buffer2 = new THREE.ReadbackBuffer( 8 );

// update cycle

const p1 = renderer.getArrayBufferAsync( attribute, buffer1, 0, 8 );
const p2 = renderer.getArrayBufferAsync( attribute, buffer2, 8, 8 );

const [ array1, array2 ] = await Promise.all( [ p1, p2 ] );

// end

buffer1.dispose();
buffer2.dispose();

Note: It will only appear if it uses the same ReadBuffer concurrently.

Notes

Based on previous feedback, I am using slice() to clone the ArrayBuffer and then discarding the mapped one; this also allowed me to remove the need for the ReadbackBuffer.release() method, making the API simpler.

/cc @gkjohnson

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	360.57 85.58	360.57 85.58	+0 B +0 B
WebGPU	635.48 176.41	635.98 176.68	+493 B +267 B
WebGPU Nodes	633.6 176.11	634.09 176.38	+493 B +267 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	492.95 120.2	492.95 120.2	+0 B +0 B
WebGPU	707.66 191.31	708.16 191.58	+496 B +272 B
WebGPU Nodes	656.88 178.57	657.38 178.84	+496 B +269 B

[sunag]

Closing in favor of #33322