Provide a useful default style

[tschaub]

Currently, the ol.feature.defaultFeatureStyleFunction results in nothing being rendered. I think we'll end up with fewer confused users if we either require a styleFunction to be provided, or provide a useful default.

[bartvde]

I agree this makes sense, and will lead to less confusion

[twpayne]

The following comment uses stroke styles as an example, but it equally applies to fill styles, text styles, and the various combinations of the presence or otherwise of each type of style.

With no default stroke style, there are two states.

1. The user supplied a stroke styles, so use it for rendering.
2. The user did not supply a stroke style, so don't render strokes.

With a default stroke style, there are three states:

1. The user supplied a style, so use it for rendering.
2. The user did not supply a stroke style, so don't render strokes.
3. The user did not supply a stroke style, so render strokes using the default stroke style.
   Distinguishing between states (2) and (3) may require some careful coding.

In an early prototype version, we used an ol.style.Stroke to indicate a stroke style set by the user, null to indicate that no stroke should be drawn, and undefined to indicate that the default stroke style should be used. However, this code proved tricky to write and we abandoned it for the simpler two-state model of stroke/no stroke.

[tschaub]

Understood. That would be an issue if we were trying to provide default symbolizers. I was talking about providing a default style function. See my default-style branch for a quick example. Basically, if the user provides anything, use it. If not, render something anyway.

[twpayne]

OK, that makes sense. But why you no use BADA55 color ?

[tschaub]

🤘

[tschaub]

Clearly a subjective thing, but I think this is a suitable default style (this is the GeoJSON example without all the style cruft).

I'm inclined to clean up our examples to be more single purpose. For example, the GeoJSON example would use the default style (and wouldn't use ol.geom.Circle), we'd have dedicated examples showing the use of the style option with and without a function, etc.

Comments?

[twpayne]

+1 from me. The GeoJSON example started as a test bed for all the different geometry types in GeoJSON, but as evolved into a base example where different geometry types are needed for demonstration/testing (e.g. the modify features example is based on it). So, there's a lot of cruft in there that can - as you say - be removed.

[elemoine]

+1 from me as well.

[bartvde]

I'd be interested to see what this looks like on a satellite type of base map but +1 from me as well

[tonio]

👍

[tschaub]

I'd be interested to see what this looks like on a satellite type of base map but +1 from me as well

It looks pretty close to the existing vector layer example.

We can continue tweaking this style - not critical to have it perfect right now, more important to have a place where the default is specified. In particular, I think we might want to have wider strokes for line geometries (and narrower for polygon), but this can be changed later.