Allow to define draw function in hpainer

[linev]

Add possibility to set draw function in hpainter

Provide demo for node.js

[danielch02]

First of all, thank you for implementing this functionality.
Please correct me if I’m wrong, but in cases where we switch between the JSROOT environment and our 3D environment, we could first store the original/default draw function and then, when toggling between the 2D and 3D environments, swap between the default draw function and our custom one accordingly. Is that correct? If so, that should be more than sufficient for our needs, and we’ll be able to achieve the functionality from our design.

[linev]

In the example I show how original draw function is called from custom one.
So you can freely define that happens in the draw.

The only special case is TTree::Draw() - there original draw first perform TTree scan and then create plots.
But this is special task and one can discuss it later.

[danielch02]

Right, understood — since we don’t need to handle special case like the TTree scan, it should work perfectly for our needs. Thanks for the clarification!