public void snapshot (Callback<SnapshotResult, Void> callback, SnapshotParameters params, WritableImage image)

Takes a snapshot of this node at the next frame and calls the specified callback method when the image is ready. CSS and layout processing will be done for the node, and any of its children, prior to rendering it. The entire destination image is cleared to the fill Paint specified by the SnapshotParameters. This node is then rendered to the image. If the viewport specified by the SnapshotParameters is null, the upper-left pixel of the boundsInParent of this node, after first applying the transform specified by the SnapshotParameters, is mapped to the upper-left pixel (0,0) in the image. If a non-null viewport is specified, the upper-left pixel of the viewport is mapped to upper-left pixel (0,0) in the image. In both cases, this mapping to (0,0) of the image is done with an integer translation. The portion of the node that is outside of the rendered image will be clipped by the image.

This is an asynchronous call, which means that other events or animation might be processed before the node is rendered. If any such events modify the node, or any of its children, that modification will be reflected in the rendered image (just like it will also be reflected in the frame rendered to the Stage, if this node is part of a live scene graph).

When taking a snapshot of a node that is being animated, either explicitly by the application or implicitly (such as chart animation), the snapshot will be rendered based on the state of the scene graph at the moment the snapshot is taken and will not reflect any subsequent animation changes.

NOTE: In order for CSS and layout to function correctly, the node must be part of a Scene (the Scene may be attached to a Stage, but need not be).

Parameters:
callback    a class whose call method will be called when the image is ready. The SnapshotResult that is passed into the call method of the callback will contain the rendered image, the source node that was rendered, and a copy of the SnapshotParameters. The callback parameter must not be null.
params    the snapshot parameters containing attributes that will control the rendering. If the SnapshotParameters object is null, then the Scene's attributes will be used if this node is part of a scene, or default attributes will be used if this node is not part of a scene.
image    the writable image that will be used to hold the rendered node. It may be null in which case a new WritableImage will be constructed. The new image is constructed using integer width and height values that are derived either from the transformed bounds of this Node or from the size of the viewport as specified in the SnapShotParameters. These integer values are chosen such that the image will wholly contain the bounds of this Node or the specified viewport. If the image is non-null, the node will be rendered into the existing image. In this case, the width and height of the image determine the area that is rendered instead of the width and height of the bounds or viewport.

Exceptions:
IllegalStateException    if this method is called on a thread other than the JavaFX Application Thread.
NullPointerException    if the callback parameter is null.

Since:  JavaFX 2.2