feat(TileLayer): Add overdraw prop

[felixpalmer]

Background

The extent prop in TileLayer controls whether tiles are fetched & drawn when the viewport zoom is below minZoom, but there is no mechanism to control this for zooms above maxZoom.

Change List

• Add overdraw prop (default true to maintain current behavior)
• When overdraw = false Tileset2D doesn't load any tiles in viewport
• Update website example to demonstrate how these props interact

[felixpalmer]

Good name? overzoom?

[coveralls]

coverage: 91.011% (-0.001%) from 91.012%
when pulling 41e46ba on felix/tile-layer-overdraw
into cad5eeb on master.

[Pessimistress]

It has always been a point of confusion because minZoom and maxZoom sounds symmetrical, but they work differently. There are two behaviors - visibility and fetching - that the users may want to control in underzoom/overzoom. I personally think we should have four props for each of these.

[felixpalmer]

@Pessimistress so would you be in favour of:

• minZoom: min zoom level at which tiles are fetched
• maxZoom: max zoom level at which tiles are fetched
• minDisplay: min zoom level at which tiles are displayed
• maxDisplay: max zoom level at which tiles are displayed
• extent: clipping region for tile fetches

minDisplay & maxDisplay are new, while the other keep the current behavior. We then don't need overdraw at all

[chrisgervang]

How about naming the new props:

• visibleMinZoom: min zoom level at which tiles are visible
• visibleMaxZoom: max zoom level at which tiles are visible

Along the same lines as the visible prop for layers and reads naturally ("visible at min zoom")

[ibgreen]

No big objections other as long as we put in some effort on the prop naming, to make this as orthogonal, expandable and intuitive as we can.

FWIW

• I have sometimes wanted a minZoom/maxZoom prop (or visibleMinZoom, visibleMaxZoom or ...) prop on all layers.
• One use case is that as one zooms in one can change between a more aggregated view (perhaps a point layer) and then a detailed layer (e.g. a HexagonLayer) as one gets close, but there are other use cases as well.
• I expect this can be done with the layerFilter mechanism but that is a bit clunky (centralized and non-declarative).

Just mill for the grist if we are ideating about such props.