[core, ios, android, qt] Observe style layer mutations rather than requiring SDKs to use Map::update

This paves the way for updates to filter and layout properties to trigger a source reload, without each SDK having to participate in the implementation.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/mbgl/style/layer_observer.hpp b/src/mbgl/style/layer_observer.hpp
new file mode 100644
index 0000000000..1d3d1aef46
--- /dev/null
+++ b/src/mbgl/style/layer_observer.hpp
@@ -0,0 +1,18 @@
+#pragma once
+
+namespace mbgl {
+namespace style {
+
+class Layer;
+
+class LayerObserver {
+public:
+    virtual ~LayerObserver() = default;
+
+    virtual void onLayerFilterChanged(Layer&) {}
+    virtual void onLayerPaintPropertyChanged(Layer&) {}
+    virtual void onLayerLayoutPropertyChanged(Layer&) {}
+};
+
+} // namespace style
+} // namespace mbgl