WebGLRenderer.readRenderTargetPixels: add parameter to select active cube face...

WebGLRenderer.readRenderTargetPixels: add parameter to select active cube face from WebGLRenderTargetCube

docs/api/en/renderers/WebGLRenderer.html

@@ -394,11 +394,11 @@
 		<h3>[method:null resetGLState]( )</h3>
 		<p>Reset the GL state to default. Called internally if the WebGL context is lost.</p>
 
-		<h3>[method:null readRenderTargetPixels]( [param:WebGLRenderTarget renderTarget], [param:Float x], [param:Float y], [param:Float width], [param:Float height], [param:TypedArray buffer] )</h3>
+		<h3>[method:null readRenderTargetPixels]( [param:WebGLRenderTarget renderTarget], [param:Float x], [param:Float y], [param:Float width], [param:Float height], [param:TypedArray buffer], [param:Integer activeCubeFaceIndex] )</h3>
 		<p>buffer - Uint8Array is the only destination type supported in all cases, other types are renderTarget and platform dependent. See [link:https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.12 WebGL spec] for details.</p>
 		<p>Reads the pixel data from the renderTarget into the buffer you pass in. This is a wrapper around [link:https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/readPixels WebGLRenderingContext.readPixels]().</p>
-		<p>See the [example:webgl_interactive_cubes_gpu interactive / cubes / gpu] example.
-		</p>
+		<p>See the [example:webgl_interactive_cubes_gpu interactive / cubes / gpu] example.</p>
+		<p>For reading out a [page:WebGLRenderTargetCube WebGLRenderTargetCube] use the optional parameter activeCubeFaceIndex to determine which face should be read.</p>
 
 
 		<h3>[method:null render]( [param:Scene scene], [param:Camera camera] )</h3>

src/renderers/WebGLRenderer.d.ts

@@ -379,7 +379,8 @@ export class WebGLRenderer implements Renderer {
     y: number,
     width: number,
     height: number,
-    buffer: any
+    buffer: any,
+    activeCubeFaceIndex?: number
   ): void;
 
   /**

src/renderers/WebGLRenderer.js

@@ -2501,7 +2501,7 @@ function WebGLRenderer( parameters ) {
 
 	};
 
-	this.readRenderTargetPixels = function ( renderTarget, x, y, width, height, buffer ) {
+	this.readRenderTargetPixels = function ( renderTarget, x, y, width, height, buffer, activeCubeFaceIndex ) {
 
 		if ( ! ( renderTarget && renderTarget.isWebGLRenderTarget ) ) {
 
@@ -2512,6 +2512,12 @@ function WebGLRenderer( parameters ) {
 
 		var framebuffer = properties.get( renderTarget ).__webglFramebuffer;
 
+		if ( activeCubeFaceIndex != undefined ) {
+
+			framebuffer = framebuffer[ activeCubeFaceIndex ];
+
+		}
+
 		if ( framebuffer ) {
 
 			var restore = false;