Duffer Derek

function WebGLAttributes( gl ) {

	const buffers = new WeakMap();

	function createBuffer( attribute, bufferType ) {

		const array = attribute.array;
		const usage = attribute.usage;
		const size = array.byteLength;

		const buffer = gl.createBuffer();

		gl.bindBuffer( bufferType, buffer );
		gl.bufferData( bufferType, array, usage );

		attribute.onUploadCallback();

		let type;

		if ( array instanceof Float32Array ) {

			type = gl.FLOAT;

		} else if ( array instanceof Uint16Array ) {

			if ( attribute.isFloat16BufferAttribute ) {

				type = gl.HALF_FLOAT;

			} else {

				type = gl.UNSIGNED_SHORT;

			}

		} else if ( array instanceof Int16Array ) {

			type = gl.SHORT;

		} else if ( array instanceof Uint32Array ) {

			type = gl.UNSIGNED_INT;

		} else if ( array instanceof Int32Array ) {

			type = gl.INT;

		} else if ( array instanceof Int8Array ) {

			type = gl.BYTE;

		} else if ( array instanceof Uint8Array ) {

			type = gl.UNSIGNED_BYTE;

		} else if ( array instanceof Uint8ClampedArray ) {

			type = gl.UNSIGNED_BYTE;

		} else {

			throw new Error( 'THREE.WebGLAttributes: Unsupported buffer data format: ' + array );

		}

		return {
			buffer: buffer,
			type: type,
			bytesPerElement: array.BYTES_PER_ELEMENT,
			version: attribute.version,
			size: size
		};

	}

	function updateBuffer( buffer, attribute, bufferType ) {

		const array = attribute.array;
		const updateRanges = attribute.updateRanges;

		gl.bindBuffer( bufferType, buffer );

		if ( updateRanges.length === 0 ) {

			// Not using update ranges
			gl.bufferSubData( bufferType, 0, array );

		} else {

			// Before applying update ranges, we merge any adjacent / overlapping
			// ranges to reduce load on `gl.bufferSubData`. Empirically, this has led
			// to performance improvements for applications which make heavy use of
			// update ranges. Likely due to GPU command overhead.
			//
			// Note that to reduce garbage collection between frames, we merge the
			// update ranges in-place. This is safe because this method will clear the
			// update ranges once updated.

			updateRanges.sort( ( a, b ) => a.start - b.start );

			// To merge the update ranges in-place, we work from left to right in the
			// existing updateRanges array, merging ranges. This may result in a final
			// array which is smaller than the original. This index tracks the last
			// index representing a merged range, any data after this index can be
			// trimmed once the merge algorithm is completed.
			let mergeIndex = 0;

			for ( let i = 1; i < updateRanges.length; i ++ ) {

				const previousRange = updateRanges[ mergeIndex ];
				const range = updateRanges[ i ];

				// We add one here to merge adjacent ranges. This is safe because ranges
				// operate over positive integers.
				if ( range.start <= previousRange.start + previousRange.count + 1 ) {

					previousRange.count = Math.max(
						previousRange.count,
						range.start + range.count - previousRange.start
					);

				} else {

					++ mergeIndex;
					updateRanges[ mergeIndex ] = range;

				}

			}

			// Trim the array to only contain the merged ranges.
			updateRanges.length = mergeIndex + 1;

			for ( let i = 0, l = updateRanges.length; i < l; i ++ ) {

				const range = updateRanges[ i ];

				gl.bufferSubData( bufferType, range.start * array.BYTES_PER_ELEMENT,
					array, range.start, range.count );

			}

			attribute.clearUpdateRanges();

		}

		attribute.onUploadCallback();

	}

	//

	function get( attribute ) {

		if ( attribute.isInterleavedBufferAttribute ) attribute = attribute.data;

		return buffers.get( attribute );

	}

	function remove( attribute ) {

		if ( attribute.isInterleavedBufferAttribute ) attribute = attribute.data;

		const data = buffers.get( attribute );

		if ( data ) {

			gl.deleteBuffer( data.buffer );

			buffers.delete( attribute );

		}

	}

	function update( attribute, bufferType ) {

		if ( attribute.isInterleavedBufferAttribute ) attribute = attribute.data;

		if ( attribute.isGLBufferAttribute ) {

			const cached = buffers.get( attribute );

			if ( ! cached || cached.version < attribute.version ) {

				buffers.set( attribute, {
					buffer: attribute.buffer,
					type: attribute.type,
					bytesPerElement: attribute.elementSize,
					version: attribute.version
				} );

			}

			return;

		}

		const data = buffers.get( attribute );

		if ( data === undefined ) {

			buffers.set( attribute, createBuffer( attribute, bufferType ) );

		} else if ( data.version < attribute.version ) {

			if ( data.size !== attribute.array.byteLength ) {

				throw new Error( 'THREE.WebGLAttributes: The size of the buffer attribute\'s array buffer does not match the original size. Resizing buffer attributes is not supported.' );

			}

			updateBuffer( data.buffer, attribute, bufferType );

			data.version = attribute.version;

		}

	}

	return {

		get: get,
		remove: remove,
		update: update

	};

}


export { WebGLAttributes };