Don't permanently crossfade fill patterns.

js: 00e11591106dae7eb02eff0328364d8ec03fdaa5

3 files changed, 43 insertions, 3 deletions

diff --git a/src/mbgl/renderer/painter.cpp b/src/mbgl/renderer/painter.cpp
index 0c17d52b5d..f4b6b80e2e 100644
--- a/src/mbgl/renderer/painter.cpp
+++ b/src/mbgl/renderer/painter.cpp
@@ -232,7 +232,7 @@ void Painter::render(const Style& style, const std::set<util::ptr<StyleSource>>&
 
     drawClippingMasks(sources);
 
-    frameHistory.record(time, state.getNormalizedZoom());
+    recordZoom(time, state.getNormalizedZoom());
 
     // Actually render the layers
     if (debug::renderTree) { std::cout << "{" << std::endl; indent++; }
@@ -459,3 +459,26 @@ mat4 Painter::translatedMatrix(const mat4& matrix, const std::array<float, 2> &t
         return vtxMatrix;
     }
 }
+
+void Painter::recordZoom(const timestamp time, const float zoom) {
+    frameHistory.record(time, zoom);
+
+    if (lastZoom < 0) {
+        // first frame ever
+        lastIntegerZoom = std::floor(zoom);
+        lastZoom = zoom;
+    }
+
+    // check whether an integer zoom level was passed since the last frame
+    // and if yes, record it with the time. Used for transitioning patterns.
+    if (std::floor(lastZoom) < std::floor(zoom)) {
+        lastIntegerZoom = std::floor(zoom);
+        lastIntegerZoomTime = time;
+
+    } else if (std::floor(lastZoom) > std::floor(zoom)) {
+        lastIntegerZoom = std::floor(zoom) + 1;
+        lastIntegerZoomTime = time;
+    }
+
+    lastZoom = zoom;
+}
diff --git a/src/mbgl/renderer/painter.hpp b/src/mbgl/renderer/painter.hpp
index 4d4876a6f1..5a42070200 100644
--- a/src/mbgl/renderer/painter.hpp
+++ b/src/mbgl/renderer/painter.hpp
@@ -139,6 +139,7 @@ private:
     mat4 translatedMatrix(const mat4& matrix, const std::array<float, 2> &translation, const Tile::ID &id, TranslateAnchorType anchor);
 
     void prepareTile(const Tile& tile);
+    void recordZoom(const timestamp time, const float zoom);
 
     template <typename BucketProperties, typename StyleProperties>
     void renderSDF(SymbolBucket &bucket,
@@ -191,6 +192,10 @@ private:
     RenderPass pass = RenderPass::Opaque;
     const float strata_epsilon = 1.0f / (1 << 16);
 
+    int lastIntegerZoom;
+    timestamp lastIntegerZoomTime = 0;
+    float lastZoom = -1;
+
 public:
     FrameHistory frameHistory;
 
diff --git a/src/mbgl/renderer/painter_fill.cpp b/src/mbgl/renderer/painter_fill.cpp
index 324dacfcd5..5e8f46d340 100644
--- a/src/mbgl/renderer/painter_fill.cpp
+++ b/src/mbgl/renderer/painter_fill.cpp
@@ -60,8 +60,20 @@ void Painter::renderFill(FillBucket& bucket, util::ptr<StyleLayer> layer_desc, c
         // Image fill.
         if (pass == RenderPass::Translucent) {
             const SpriteAtlasPosition pos = spriteAtlas.getPosition(properties.image, true);
-            const float mix = std::fmod(float(state.getZoom()), 1.0f);
-            const float factor = 8.0 / std::pow(2, state.getIntegerZoom() - id.z);
+            float factor = 8.0 / std::pow(2, state.getIntegerZoom() - id.z);
+
+            float mix;
+            float duration = 300 * 1_millisecond;
+            const float fraction = std::fmod(float(state.getZoom()), 1.0f);
+            float t = std::min((util::now() - lastIntegerZoomTime) / duration, 1.0f);
+            if (state.getZoom() > lastIntegerZoom) {
+                // zooming in
+                mix = fraction + (1.0f - fraction) * t;
+                factor *= 2.0;
+            } else {
+                // zooming out
+                mix = fraction - fraction * t;
+            }
 
             mat3 patternMatrix;
             matrix::identity(patternMatrix);