From b5a5dfc34a2befef0cc2f09fce12d833c4bba901 Mon Sep 17 00:00:00 2001
From: Quincy Morgan <quincy.morgan@icloud.com>
Date: Fri, 22 Nov 2019 12:14:20 -0500
Subject: [PATCH] Don't list non-global imagery sources at low zooms (close
 #7062) Always show the currently selected background in the list (close
 #7061)

---
 modules/renderer/background.js | 16 ++++++++++++++--
 modules/ui/background.js       |  2 +-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/modules/renderer/background.js b/modules/renderer/background.js
index 0bbaf5a25..ce7416e7b 100644
--- a/modules/renderer/background.js
+++ b/modules/renderer/background.js
@@ -212,15 +212,27 @@ export function rendererBackground(context) {
     };
 
 
-    background.sources = function(extent) {
+    background.sources = function(extent, zoom, alwaysIncludeSelected) {
         if (!data.imagery || !data.imagery.query) return [];   // called before init()?
 
         var matchIDs = {};
         var matchImagery = data.imagery.query.bbox(extent.rectangle(), true) || [];
         matchImagery.forEach(function(d) { matchIDs[d.id] = true; });
 
+        var currentSource = baseLayer.source();
+
         return _backgroundSources.filter(function(source) {
-            return matchIDs[source.id] || !source.polygon;   // no polygon = worldwide
+            // optionally always include the selected source
+            if (alwaysIncludeSelected && currentSource === source) return true;
+
+            // always show sources with worldwide coverage
+            if (!source.polygon) return true;
+
+            // optionally don't include non-worldwide sources at low zooms
+            if (zoom && zoom < 6) return false;
+
+            // don't include sources outside the extent
+            return matchIDs[source.id];
         });
     };
 
diff --git a/modules/ui/background.js b/modules/ui/background.js
index e8ada1956..6a15fb0ff 100644
--- a/modules/ui/background.js
+++ b/modules/ui/background.js
@@ -121,7 +121,7 @@ export function uiBackground(context) {
 
     function drawListItems(layerList, type, change, filter) {
         var sources = context.background()
-            .sources(context.map().extent())
+            .sources(context.map().extent(), context.map().zoom(), true)
             .filter(filter);
 
         var layerLinks = layerList.selectAll('li')