Questions about property- and property-zoom functions

davidtheclark commented 7 years ago

I'm trying to build a first-draft UI for these in Studio and ran into a few questions. I didn't find answers in the style spec docs, so I'm thinking that maybe when I have answers I'll try to add them to the docs:

Is there a minimum number of stops for property- or property-zoom functions? (Or zoom functions for that matter. I know in Studio we're enforcing a minimum of two, but does the spec require that?)
How do you set a fallback property value? I suppose with any interpolatable property you could interpolate every necessary value as long as you have two stops to create a function with (^^). But for non-interpolatable properties, you'd be in a pickle. For example, let's say your reference field is a string field like name, and you don’t provide a stop for every possible value: how can you control what happens when name does not match a stop? I want "Mexico" to be red, "Canada" to be purple, and everything else to be pink.
In the style-spec JSON itself, does property-function: true mean both property-function and property-zoom-function, or do no properties have property-zoom-function support yet?

davidtheclark commented 7 years ago

cc @mapbox/appbox

jfirebaugh commented 7 years ago

Is there a minimum number of stops for property- or property-zoom functions?

The minimum is 1. This is enforced by the validator.

How do you set a fallback property value?

I filed #582 related to this, and #480 is also related.

Does property-function: true mean both property-function and property-zoom-function

Yes. Note that you can't really rely on this property for anything meaningful because it indicates which properties could conceivably someday support data-driven functions, not which ones actually do. I think we should probably remove it in favor of sdk-support['data-driven styling'].

davidtheclark commented 7 years ago

I think we should probably remove it in favor of sdk-support['data-driven styling']

If 'data-driven styling' is supported, then, it will favor both types of functions, right?

jfirebaugh commented 7 years ago

Correct.

mapbox / mapbox-gl-style-spec

Questions about property- and property-zoom functions #586