handle wrapX without calculating excess meridians

avoid calculating more meridians or longer parallels than necessary when viewport extent includes a wrapped world

src/ol/layer/Graticule.js

@@ -717,6 +717,22 @@ class Graticule extends VectorLayer {
       return;
     }
 
+    let wrapX = false;
+    const projectionExtent = this.projection_.getExtent();
+    const worldWidth = getWidth(projectionExtent);
+    if (this.getSource().getWrapX() && this.projection_.canWrapX() && !containsExtent(projectionExtent, extent)) {
+      if (getWidth(extent) >= worldWidth) {
+        extent[0] = projectionExtent[0];
+        extent[2] = projectionExtent[2];
+      } else {
+        const worldsAway = Math.floor((center[0] - projectionExtent[0]) / worldWidth);
+        center[0] -= (worldsAway * worldWidth);
+        extent[0] -= (worldsAway * worldWidth);
+        extent[2] -= (worldsAway * worldWidth);
+        wrapX = true;
+      }
+    }
+
     // Constrain the center to fit into the extent available to the graticule
 
     const validCenterP = [
@@ -740,44 +756,56 @@ class Graticule extends VectorLayer {
 
     // Limit the extent to fit into the extent available to the graticule
 
-    const validExtentP = [
+    let validExtentP = extent;
+    if (!wrapX) {
+      validExtentP = [
         clamp(extent[0], this.minX_, this.maxX_),
         clamp(extent[1], this.minY_, this.maxY_),
         clamp(extent[2], this.minX_, this.maxX_),
         clamp(extent[3], this.minY_, this.maxY_)
       ];
+    }
 
     // Transform the extent to get the lon lat ranges for the edges of the extent
 
     const validExtent = applyTransform(validExtentP, this.toLonLatTransform_, undefined, 8);
 
+    let maxLat = validExtent[3];
+    let maxLon = validExtent[2];
+    let minLat = validExtent[1];
+    let minLon = validExtent[0];
+
+    if (!wrapX) {
+
       // Check if extremities of the world extent lie inside the extent
       // (for example the pole in a polar projection)
       // and extend the extent as appropriate
 
       if (containsCoordinate(validExtentP, this.bottomLeft_)) {
-      validExtent[0] = this.minLon_;
+        minLon = this.minLon_;
-      validExtent[1] = this.minLat_;
+        minLat = this.minLat_;
       }
       if (containsCoordinate(validExtentP, this.bottomRight_)) {
-      validExtent[2] = this.maxLon_;
+        maxLon = this.maxLon_;
-      validExtent[1] = this.minLat_;
+        minLat = this.minLat_;
       }
       if (containsCoordinate(validExtentP, this.topLeft_)) {
-      validExtent[0] = this.minLon_;
+        minLon = this.minLon_;
-      validExtent[3] = this.maxLat_;
+        maxLat = this.maxLat_;
       }
       if (containsCoordinate(validExtentP, this.topRight_)) {
-      validExtent[2] = this.maxLon_;
+        maxLon = this.maxLon_;
-      validExtent[3] = this.maxLat_;
+        maxLat = this.maxLat_;
       }
 
       // The transformed center may also extend the lon lat ranges used for rendering
 
-    const maxLat = clamp(validExtent[3], centerLat, this.maxLat_);
+      maxLat = clamp(maxLat, centerLat, this.maxLat_);
-    const maxLon = clamp(validExtent[2], centerLon, this.maxLon_);
+      maxLon = clamp(maxLon, centerLon, this.maxLon_);
-    const minLat = clamp(validExtent[1], this.minLat_, centerLat);
+      minLat = clamp(minLat, this.minLat_, centerLat);
-    const minLon = clamp(validExtent[0], this.minLon_, centerLon);
+      minLon = clamp(minLon, this.minLon_, centerLon);
+
+    }
 
     // Create meridians
 
@@ -787,18 +815,30 @@ class Graticule extends VectorLayer {
     idx = this.addMeridian_(lon, minLat, maxLat, squaredTolerance, extent, 0);
 
     cnt = 0;
+    if (wrapX) {
+      while ((lon -= interval) >= minLon && cnt++ < maxLines) {
+        idx = this.addMeridian_(lon, minLat, maxLat, squaredTolerance, extent, idx);
+      }
+    } else {
       while (lon != this.minLon_ && cnt++ < maxLines) {
         lon = Math.max(lon - interval, this.minLon_);
         idx = this.addMeridian_(lon, minLat, maxLat, squaredTolerance, extent, idx);
       }
+    }
 
     lon = clamp(centerLon, this.minLon_, this.maxLon_);
 
     cnt = 0;
+    if (wrapX) {
+      while ((lon += interval) <= maxLon && cnt++ < maxLines) {
+        idx = this.addMeridian_(lon, minLat, maxLat, squaredTolerance, extent, idx);
+      }
+    } else {
       while (lon != this.maxLon_ && cnt++ < maxLines) {
         lon = Math.min(lon + interval, this.maxLon_);
         idx = this.addMeridian_(lon, minLat, maxLat, squaredTolerance, extent, idx);
       }
+    }
 
     this.meridians_.length = idx;
     if (this.meridiansLabels_) {