ImageOverlayPlugin: Improvements

[gkjohnson]

Performance & Preload

• Add an asynchronous option for tile splitting to avoid framerate hiccups. Either add to a priority queue or perform one iteration per frame.
• Instead of blocking on image loading we should display the best loaded parent tiles until the necessary ones are ready. Or cascade the parent tile loads downward.
• Afford a more intelligent selection of tile mapping layer to tiles (Allow higher zoom level overlay than "master" tileset tile's using ImageOverlayPlugin #1278)
  • Can compute some implicit geometric error for the tiles.
  • Calculate target overlay resolution based on the size of the bounds of the tile and associated image tile resolution rather than using a fixed 256x dimension texture.

Quality

• Add option for fading images in after they've loaded
• Add option for not showing a new layer until all images are loaded
• Add a custom priority queue function to ensure most relevant tiles are loaded ASAP
  • Load images for "visible", "in frustum" and "used" tiles first.
• Consider drawing lower-res versions of tiles if high-res versions aren't present to enable more dynamic updates? Ideally we could update child tiles when parent LoDs load but this is more complex.
  • Could be done in the "onTileVisible" callback such that if the data isn't loaded yet we can draw the next best complete data set.
• Add preload for tile when using planar projection. Requires projecting the bounds into the tiled image space.
• Add support for frustum transform frames
  • eg when projecting a high res camera view
• TileSplitting: Detect if using quantized mesh and switch to QuantizedMesh clipper, instead?
• TileSplitting: Add support for mesh ranges, multi material.

Other

• Allow for mipmap generation option?