o Implemented the missingTilesDepth feature (issue #73), which tries to take mis…

…sing tiles from lower zoom levels

@@ -27,7 +27,6 @@
 
 #import "RMAbstractWebMapSource.h"
 #import "RMTileCache.h"
-#import "RMTileImage.h"
 
 @implementation RMAbstractWebMapSource
 
@@ -148,9 +147,6 @@
         [[NSNotificationCenter defaultCenter] postNotificationName:RMTileRetrieved object:[NSNumber numberWithUnsignedLongLong:RMTileKey(tile)]];
     });
 
-    if (!image)
-        return [RMTileImage errorTile];
-
     return image;
 }
 

@@ -10,6 +10,7 @@
 
 #import "RMMapView.h"
 #import "RMTileSource.h"
+#import "RMTileImage.h"
 
 @interface RMMapOverlayView ()
 
@@ -132,6 +133,50 @@
         UIGraphicsPushContext(context);
 
         UIImage *tileImage = [[mapView tileSource] imageForTile:RMTileMake(x, y, zoom) inCache:[mapView tileCache]];
+
+        if ( ! tileImage)
+        {
+            if (mapView.missingTilesDepth == 0)
+            {
+                tileImage = [RMTileImage errorTile];
+            }
+            else
+            {
+                NSUInteger currentTileDepth = 1, currentZoom = zoom - currentTileDepth;
+
+                // tries to return lower zoom level tiles if a tile cannot be found
+                while ( !tileImage && currentZoom >= mapView.tileSource.minZoom && currentTileDepth <= mapView.missingTilesDepth)
+                {
+                    float nextX = x / powf(2.0, (float)currentTileDepth),
+                          nextY = y / powf(2.0, (float)currentTileDepth);
+                    float nextTileX = floor(nextX),
+                          nextTileY = floor(nextY);
+
+                    tileImage = [[mapView tileSource] imageForTile:RMTileMake((int)nextTileX, (int)nextTileY, currentZoom) inCache:[mapView tileCache]];
+
+                    if (tileImage)
+                    {
+                        // crop
+                        float cropSize = 1.0 / powf(2.0, (float)currentTileDepth);
+
+                        CGRect cropBounds = CGRectMake(tileImage.size.width * (nextX - nextTileX),
+                                                       tileImage.size.height * (nextY - nextTileY),
+                                                       tileImage.size.width * cropSize,
+                                                       tileImage.size.height * cropSize);
+
+                        CGImageRef imageRef = CGImageCreateWithImageInRect([tileImage CGImage], cropBounds);
+                        tileImage = [UIImage imageWithCGImage:imageRef];
+                        CGImageRelease(imageRef);
+
+                        break;
+                    }
+
+                    currentTileDepth++;
+                    currentZoom = zoom - currentTileDepth;
+                }
+            }
+        }
+
         [tileImage drawInRect:rect];
 
         UIGraphicsPopContext();

@@ -69,12 +69,9 @@ typedef enum {
 {
     id <RMMapViewDelegate> delegate;
 
-    /// projection objects to convert from latitude/longitude to meters,
-    /// from projected meters to tile coordinates
     RMProjection *projection;
     RMFractalTileProjection *mercatorToTileProjection;
 
-    /// subview for the background image displayed while tiles are loading. Set its contents by providing your own "loading.png".
     UIView *backgroundView;
     RMMapScrollView *mapScrollView;
     RMMapTiledLayerView *tiledLayerView;
@@ -92,10 +89,10 @@ typedef enum {
     id <RMTileSource> tileSource;
     RMTileCache *tileCache; // Generic tile cache
 
-    /// minimum and maximum zoom number allowed for the view. #minZoom and #maxZoom must be within the limits of #tileSource but can be stricter; they are clamped to tilesource limits if needed.
     float minZoom, maxZoom, zoom;
     float screenScale;
 
+    NSUInteger missingTilesDepth;
     NSUInteger boundingMask;
 }
 
@@ -117,27 +114,34 @@ typedef enum {
 @property (nonatomic, readonly) double scaledMetersPerPixel;
 @property (nonatomic, readonly) double scaleDenominator; /// The denominator in a cartographic scale like 1/24000, 1/50000, 1/2000000.
 @property (nonatomic, readonly) float screenScale;
-@property (nonatomic, assign)   NSUInteger boundingMask;
 
 @property (nonatomic, assign)   BOOL adjustTilesForRetinaDisplay;
 @property (nonatomic, readonly) float adjustedZoomForRetinaDisplay; // takes adjustTilesForRetinaDisplay and screen scale into account
 
-@property (nonatomic, assign) float zoom; /// zoom level is clamped to range (minZoom, maxZoom)
+/// minimum and maximum zoom number allowed for the view. #minZoom and #maxZoom must be within the limits of #tileSource but can be stricter; they are clamped to tilesource limits (minZoom, maxZoom) if needed.
+@property (nonatomic, assign) float zoom;
 @property (nonatomic, assign) float minZoom;
 @property (nonatomic, assign) float maxZoom;
 
+/// take missing tiles from lower zoom levels, up to #missingTilesDepth zoom levels (defaults to 0, which disables this feature)
+@property (nonatomic, assign) NSUInteger missingTilesDepth;
+
+@property (nonatomic, assign)   NSUInteger boundingMask;
+
 @property (nonatomic, retain) RMQuadTree *quadTree;
 @property (nonatomic, assign) BOOL enableClustering;
 @property (nonatomic, assign) BOOL positionClusterMarkersAtTheGravityCenter;
 @property (nonatomic, assign) CGSize clusterMarkerSize;
 @property (nonatomic, assign) CGSize clusterAreaSize;
 
+/// projection objects to convert from latitude/longitude to meters, from projected meters to tile coordinates
 @property (nonatomic, readonly) RMProjection *projection;
 @property (nonatomic, readonly) id <RMMercatorToTileProjection> mercatorToTileProjection;
 
 @property (nonatomic, retain) id <RMTileSource> tileSource;
 @property (nonatomic, retain) RMTileCache *tileCache;
 
+/// subview for the background image displayed while tiles are loading.
 @property (nonatomic, retain) UIView *backgroundView;
 
 #pragma mark -

@@ -117,6 +117,7 @@
 @synthesize quadTree;
 @synthesize enableClustering, positionClusterMarkersAtTheGravityCenter, clusterMarkerSize, clusterAreaSize;
 @synthesize adjustTilesForRetinaDisplay;
+@synthesize missingTilesDepth;
 
 #pragma mark -
 #pragma mark Initialization
@@ -144,6 +145,7 @@
 
     boundingMask = RMMapMinWidthBound;
     adjustTilesForRetinaDisplay = NO;
+    missingTilesDepth = 0;
 
     annotations = [NSMutableSet new];
     visibleAnnotations = [NSMutableSet new];