More SymbolLayer properties + sourceLayerIdentifier support + zoom levels + local image support

[hactar]

Sorry for conglomerate of different changes - these were missing features we needed for a testflight release.

• Added multiple properties to the SymbolLayer so one can set more of the text attributes that were missing.
• Added support for specifying zoom levels. It works, but there was some zoom level code already, so please verify that what I added is as intended.
• Added support for dynamic images on the SymbolLayer. It is similar to the code you had, but uses "keyPath" instead of "attribute" to access the feature property.
• Added sourceLayerIdentifier (https://maplibre.org/maplibre-native/ios/latest/documentation/maplibre/mlnvectorstylelayer/sourcelayeridentifier), needed to be able to access a specific source layer combined with MLNSource.

Here is a screenshot from our app, using all these features (notice the text, halos, dynamic images created locally from sf symbols, etc - all this is loaded from a source in the style json):

Tests do not pass, I will update the PR once #41 is merged.

[hactar]

Please review if this how you picture its usage, as I see other zoom level code in this spm already, but didn't find a way to access it from the MapView view builder.

[ianthetechie]

@Archdoog on our review call: "I think he is on to something fantastic" 😂 We definitely missed exposing this idiomatically in the high-level StyleLayerDefinition!

Capturing another random thought: it might make sense to split this file up since it's now got a bunch of random crap in it :) Especially for things like modifiers which might not be as obvious/discoverable. (Can do this later.)

[hactar]

I made these two public, because this allows devs to make their own extensions for the SymbolStyleLayer. For example, we created a helper extension for ourselves like this, but needed these properties exposed to do so:

public extension SymbolStyleLayer {

    func iconImage(mappings: [AnyHashable: UIImage], default defaultImage: UIImage) -> Self {
        return modified(self) { it in

            let expression1 = NSExpression(forKeyPath: "ios_category_icon_name")
            let expression2 = NSExpression(forKeyPath: "ios_category_icon_color")

            // Create an NSExpression that concatenates the two key paths
            let attributeExpression = expression1.mgl_appending(expression2)
            let mappingExpressions = mappings.mapValues { image in
                NSExpression(forConstantValue: image.sha256())
            }
            let mappingDictionary = NSDictionary(dictionary: mappingExpressions)
            let defaultExpression = NSExpression(forConstantValue: defaultImage.sha256())

            // swiftlint:disable force_cast
            it.iconImageName = NSExpression(
                forMLNMatchingKey: attributeExpression,
                in: mappingDictionary as! [NSExpression: NSExpression],
                default: defaultExpression
            )
            // swiftlint:enable force_cast
            it.iconImages = mappings.values + [defaultImage]
        }
    }

}

[ianthetechie]

That makes sense. Thanks for the detailed example clarifying the use case!

[ianthetechie]

This is awesome; thanks as always!

Final bit of feedback: could you implement the example that shows dynamic icon selection? There's a first pass which is currently commented out at the bottom of Examples/Layers.swift.

[ianthetechie]

@Archdoog on our review call: "I think he is on to something fantastic" 😂 We definitely missed exposing this idiomatically in the high-level StyleLayerDefinition!

Capturing another random thought: it might make sense to split this file up since it's now got a bunch of random crap in it :) Especially for things like modifiers which might not be as obvious/discoverable. (Can do this later.)

[ianthetechie]

That makes sense. Thanks for the detailed example clarifying the use case!

[hactar]

So I tried adding the example to the the example layers file, but for some reason it crashes in the Preview here (and only here). If I create an app project and add the same code, there is no crash and the code works both in preview mode and in the app.

I have no idea why this may be, I'm blaming it on the package not being a real app, but I have no proof for this. I have attached a screenshot of this working, as well as a demo app to this comment. Maybe someone else knows whats going on, or else we just don't provide an un-commented in example...

MapLibreDSLThing.zip

[ianthetechie]

🤯 whoa! What on earth?? Previews are weird, yeah, but.... okay. That's interesting. That also probably explains why, after trying several different things a few weeks ago, I never got anything that worked for image matching! I was only ever testing in the previews.

I'll take a look, but I believe that means this is probably mergeable as-is and we'll have to raise an issue upstream after collecting some more details on the crash.