[core] use stale styles

This adds support for using cached styles that are stale. They're treated like changing styles; when the refreshed style changed compared to the one we've already had, we're swapping out the entire style, which might cause a slight flicker.

2 files changed, 9 insertions, 9 deletions

diff --git a/src/mbgl/map/map_context.cpp b/src/mbgl/map/map_context.cpp
index 6f12e968bd..eb17e20aea 100644
--- a/src/mbgl/map/map_context.cpp
+++ b/src/mbgl/map/map_context.cpp
@@ -105,12 +105,6 @@ void MapContext::setStyleURL(const std::string& url) {
 
     FileSource* fs = util::ThreadContext::getFileSource();
     styleRequest = fs->request({ Resource::Kind::Style, styleURL }, [this, base](Response res) {
-        if (res.stale) {
-            // Only handle fresh responses.
-            return;
-        }
-        styleRequest = nullptr;
-
         if (res.error) {
             if (res.error->reason == Response::Error::Reason::NotFound &&
                 util::mapbox::isMapboxURL(styleURL)) {
@@ -120,9 +114,11 @@ void MapContext::setStyleURL(const std::string& url) {
                 data.loading = false;
             }
         } else {
-            loadStyleJSON(*res.data, base);
+            // We got a new stylesheet; only update when it's different from the previous one.
+            if (styleJSON != *res.data) {
+                loadStyleJSON(*res.data, base);
+            }
         }
-
     });
 }
 
@@ -132,7 +128,7 @@ void MapContext::setStyleJSON(const std::string& json, const std::string& base)
     }
 
     styleURL.clear();
-    styleJSON = json;
+    styleJSON.clear();
 
     style = std::make_unique<Style>(data);
 
@@ -144,6 +140,7 @@ void MapContext::loadStyleJSON(const std::string& json, const std::string& base)
 
     style->setJSON(json, base);
     style->setObserver(this);
+    styleJSON = json;
 
     // force style cascade, causing all pending transitions to complete.
     style->cascade();
diff --git a/src/mbgl/style/style.cpp b/src/mbgl/style/style.cpp
index fbca01311b..f64bdfc921 100644
--- a/src/mbgl/style/style.cpp
+++ b/src/mbgl/style/style.cpp
@@ -43,6 +43,9 @@ Style::Style(MapData& data_)
 }
 
 void Style::setJSON(const std::string& json, const std::string&) {
+    sources.clear();
+    layers.clear();
+
     rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> doc;
     doc.Parse<0>((const char *const)json.c_str());
     if (doc.HasParseError()) {