It look super arbitrary that we write the height and width to the heap and shift is 0 bits. You are right, it is the new helper code from the
vtkWebAssemblyRenderWindowInteractor.js.
That library code is an implementation detail in VTK. This is how it communicates the size available for rendering to VTK. In the event handler in C++, we decode the contents of the returned pointer into width and height.
Also, would it be a good idea to expose to JavaScript,
vtkInitializeCanvasElementand use this for creating additional canvases and perhapsvtkGetParentElementBoundingRectSizefor resizing canvases when resizing a canvas.
Hmm, those two are already javascript functions and could be accessible on the wasm instance. Can you try searching the generated JS for those?