Updated docs #5231

src/gameobjects/graphics/Graphics.js

@@ -1448,6 +1448,10 @@ var Graphics = new Class({
      * If `key` is a Canvas it will draw the texture to that canvas context. Note that it will NOT
      * automatically upload it to the GPU in WebGL mode.
      *
+     * Please understand that the texture is created via the Canvas API of the browser, therefore some
+     * Graphics features, such as `fillGradientStyle`, will not appear on the resulting texture,
+     * as they're unsupported by the Canvas API.
+     *
      * @method Phaser.GameObjects.Graphics#generateTexture
      * @since 3.0.0
      *