Discard attribute typed arrays for buffered geometries that are not modified after initial rendering (#9512)

* add setDiscardBuffer method to BufferGeometry

* added discard support to BufferAttribute

* add mechanism for discard of BufferAttribute TypedArrays

* use more elegant method for creating dummy typed array.

* fix typo

* Update BufferGeometry.js

fix brain fade

* rework to use callbacks (phase 1)

* rework part 2

* remove build file

* support setting onUploadCallback from Geometry

* remove repeated calculation from renderer

* remove now redundant getter

* remove geoemtry interface

* document discard mechanism.

* merge fixes

* restore return.this

* drop unneeded call()

* rename discard() method to disposeArray()

docs/api/core/BufferAttribute.html

@@ -54,6 +54,11 @@
 		A version number, incremented every time the needsUpdate property is set to true.
 		</div>
 
+		<h3>[property:Function onUploadCallback]</h3>
+		<div>
+		A callback function that is executed after the Renderer has transfered the attribute array data to the GPU.
+		The callback is executed with a single parameter "name", the name of the buffer attribute, and "this" set to the BufferAttribute object.
+		</div>
 
 		<h2>Methods</h2>
 
@@ -108,6 +113,12 @@
 		Copies this attribute.
 		</div>
 
+		<h3>[method:null disposeArray]() </h3>
+		<div>
+		Discards the typed array containing the attribute data. This can be executed after the data has been transfered to the GPU to allow the memory to be reclaimed.
+		For use where the attribute will not be changed after the discard method is called.
+		</div>
+
 		<h2>Source</h2>
 
 		[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]

src/core/BufferAttribute.js

@@ -27,6 +27,7 @@ function BufferAttribute( array, itemSize, normalized ) {
 	this.updateRange = { offset: 0, count: - 1 };
 
 	this.version = 0;
+	this.onUploadCallback = null;
 
 }
 
@@ -323,6 +324,14 @@ BufferAttribute.prototype = {
 
 		return new this.constructor().copy( this );
 
+	},
+
+	disposeArray: function () {
+
+		var oldArray = this.array;
+
+		this.array = new oldArray.constructor( 1 ); // create dummy minimal length TypedArray
+
 	}
 
 };

src/renderers/webgl/WebGLObjects.js

@@ -34,7 +34,7 @@ function WebGLObjects( gl, properties, info ) {
 
 		for ( var name in attributes ) {
 
-			updateAttribute( attributes[ name ], gl.ARRAY_BUFFER );
+			updateAttribute( attributes[ name ], gl.ARRAY_BUFFER, name );
 
 		}
 
@@ -58,7 +58,7 @@ function WebGLObjects( gl, properties, info ) {
 
 	}
 
-	function updateAttribute( attribute, bufferType ) {
+	function updateAttribute( attribute, bufferType, name ) {
 
 		var data = ( attribute.isInterleavedBufferAttribute ) ? attribute.data : attribute;
 
@@ -66,7 +66,7 @@ function WebGLObjects( gl, properties, info ) {
 
 		if ( attributeProperties.__webglBuffer === undefined ) {
 
-			createBuffer( attributeProperties, data, bufferType );
+			createBuffer( attributeProperties, data, bufferType, name );
 
 		} else if ( attributeProperties.version !== data.version ) {
 
@@ -76,7 +76,7 @@ function WebGLObjects( gl, properties, info ) {
 
 	}
 
-	function createBuffer( attributeProperties, data, bufferType ) {
+	function createBuffer( attributeProperties, data, bufferType, name ) {
 
 		attributeProperties.__webglBuffer = gl.createBuffer();
 		gl.bindBuffer( bufferType, attributeProperties.__webglBuffer );
@@ -126,6 +126,12 @@ function WebGLObjects( gl, properties, info ) {
 		attributeProperties.type = type;
 		attributeProperties.version = data.version;
 
+		if ( data.onUploadCallback ) {
+
+			data.onUploadCallback( name );
+
+		}
+
 	}
 
 	function updateBuffer( attributeProperties, data, bufferType ) {