Binding a framebuffer sets the viewport size

Author: photonstorm

src/renderer/webgl/WebGLRenderer.js

@@ -1018,20 +1018,29 @@ var WebGLRenderer = new Class({
      * @method Phaser.Renderer.WebGL.WebGLRenderer#setFramebuffer
      * @since 3.0.0
      *
-     * @param {WebGLFramebuffer} framebuffer - The framebuffer that needs to be bound
+     * @param {WebGLFramebuffer} framebuffer - The framebuffer that needs to be bound.
      *
      * @return {Phaser.Renderer.WebGL.WebGLRenderer} This WebGL Renderer.
      */
     setFramebuffer: function (framebuffer)
     {
         var gl = this.gl;
 
+        var width = this.width;
+        var height = this.height;
+
         if (framebuffer !== this.currentFramebuffer)
         {
-            this.flush();
+            if (framebuffer && framebuffer.renderTexture)
+            {
+                width = framebuffer.renderTexture.width;
+                height = framebuffer.renderTexture.height;
+            }
 
             gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
 
+            gl.viewport(0, 0, width, height);
+
             this.currentFramebuffer = framebuffer;
         }