Explore using Framebuffers

[kylebarron]

I think an initial pass to render to a framebuffer might be more performant for spectral indices, or especially complex things like Landsat level 3 products.

I think that the existing one-pass architecture re-renders every frame, so it must re-compute the spectral index every frame. For something like level 3 products, that's almost certainly too compute-intensive.

It would seem like framebuffers could make this performant, because the index only needs to be computed once. The input data is static and not changing. Then pass the index to the render pass, which only needs the index + colormap, which can be substituted on the fly. Just applying the colormap to the index should be really fast to do on the fly and while panning.