use the global animationTime instead of querying our own time

this reduces the amount of std::chrono::steady_clock::now() calls

src/mbgl/renderer/frame_history.cpp

@@ -3,7 +3,7 @@
 using namespace mbgl;
 
 // Record frame history that will be used to calculate fading params
-void FrameHistory::record(const TimePoint& now, float zoom) {
+void FrameHistory::record(const TimePoint now, float zoom) {
     // first frame ever
     if (history.empty()) {
         history.emplace_back(FrameSnapshot{TimePoint::min(), zoom});
@@ -47,15 +47,13 @@ bool FrameHistory::needsAnimation(const Duration& duration) const {
     return false;
 }
 
-FadeProperties FrameHistory::getFadeProperties(const Duration& duration) {
-    const TimePoint currentTime = Clock::now();
-
+FadeProperties FrameHistory::getFadeProperties(const TimePoint now, const Duration& duration) {
     // Remove frames until only one is outside the duration, or until there are only three
-    while (history.size() > 3 && history[1].now + duration < currentTime) {
+    while (history.size() > 3 && history[1].now + duration < now) {
         history.pop_front();
     }
 
-    if (history[1].now + duration < currentTime) {
+    if (history[1].now + duration < now) {
         history[0].z = history[1].z;
     }
 
@@ -74,7 +72,7 @@ FadeProperties FrameHistory::getFadeProperties(const Duration& duration) {
 
     // At end of a zoom when the zoom stops changing continue pretending to zoom at that speed
     // bump is how much farther it would have been if it had continued zooming at the same rate
-    float bump = std::chrono::duration<float>(currentTime - lastFrame.now) / duration * fadedist;
+    float bump = std::chrono::duration<float>(now - lastFrame.now) / duration * fadedist;
 
     return FadeProperties {
         fadedist,

src/mbgl/renderer/frame_history.hpp

@@ -11,7 +11,7 @@
 namespace mbgl {
 
 struct FrameSnapshot {
-    explicit inline FrameSnapshot(const TimePoint& now_, float z_) : now(now_), z(z_) {}
+    explicit inline FrameSnapshot(TimePoint now_, float z_) : now(now_), z(z_) {}
     const TimePoint now;
     float z;
 };
@@ -26,10 +26,10 @@ struct FadeProperties {
 class FrameHistory {
 public:
     // Record frame history that will be used to calculate fading params
-    void record(const TimePoint& now, float zoom);
+    void record(TimePoint now, float zoom);
 
     bool needsAnimation(const Duration& duration) const;
-    FadeProperties getFadeProperties(const Duration& duration);
+    FadeProperties getFadeProperties(TimePoint now, const Duration& duration);
 
 public:
     std::deque<FrameSnapshot> history;

src/mbgl/renderer/painter_symbol.cpp

@@ -53,7 +53,7 @@ void Painter::renderSDF(SymbolBucket &bucket,
 
     sdfShader.u_zoom = (state.getNormalizedZoom() - zoomAdjust) * 10; // current zoom level
 
-    FadeProperties f = frameHistory.getFadeProperties(data.getDefaultFadeDuration());
+    FadeProperties f = frameHistory.getFadeProperties(data.getAnimationTime(), data.getDefaultFadeDuration());
     sdfShader.u_fadedist = f.fadedist * 10;
     sdfShader.u_minfadezoom = std::floor(f.minfadezoom * 10);
     sdfShader.u_maxfadezoom = std::floor(f.maxfadezoom * 10);