JosephCottam
Aggregate-Zoom panel
Implement aggregate-based zooming so zoom can be done without accessing the base glyphs.
Zoom is complicated. If point-based implantations are used, then zoom can be done with the same rollup as is used in merging partial results from glyph-parallel rendering. However, this is not semantically valid for anything with extent (lines or shapes). For example: Make a checkerboard with 2x2 squares. If using a "count" aggregator for the base resolution, each filled position gets a value of 1. Now zoom out so each square is 1x1. If done with rollup aggregation, each aggregate will get the value 4, but if simply re-rendered the value would be 1. The plotting implantation (point, line, area) matter to the aggregation used to zoom.
Ideas to achieve zoom (merits unknown): A) Introduce an aggregator method for each major implantation type. B) Introduce a new top-level type "Rollup" to handle zoom (similar to an aggregator)
There may be no general-purpose exact solution...in which case Aggregate-Zoom is really Approximate zoom.
Consider a checkerboard of 5 2x2 squares rendered to the screen. As indicated above, if they have extent then simple summation is not valid for zoom-out. Max works for a small step in a checkerboard, but once items start to overlap it ceases too. For example, zoom out until the whole checkerboard fits into one pixel and Max/Min/Avg don't work either (the correct answer is to have the value 5 on the pixel, but Max/Min/Avg give 1, and sum gives 20). Without identity of the items, the correct answer can't be determined.
HOWEVER, the bounds of the correct answer can be determined, so the aggregate zoom is not worthless. It just needs to communicate that its an approximation and to please be patient while the exact answer is fetched.
Incidentally, transfer actually takes a long time as grids get larger (20s or so on a 5Kx5K grid). Roll-up zoom probably does to...
That makes me think! Roll-up zoom is a transfer function...Especially with the ItemWise specialization made separate, it might even fit nicely...