fixes #110: properly query local tile sources

@@ -12,6 +12,8 @@
 #import "RMTileSource.h"
 #import "RMTileImage.h"
 #import "RMTileCache.h"
+#import "RMMBTilesSource.h"
+#import "RMDBMapSource.h"
 
 @implementation RMMapTiledLayerView
 {
@@ -118,20 +120,31 @@
 
         if (zoom >= _tileSource.minZoom && zoom <= _tileSource.maxZoom)
         {
-            tileImage = [[_mapView tileCache] cachedImage:RMTileMake(x, y, zoom) withCacheKey:[_tileSource uniqueTilecacheKey]];
-
-            if ( ! tileImage)
+            if ([_tileSource isKindOfClass:[RMMBTilesSource class]] || [_tileSource isKindOfClass:[RMDBMapSource class]])
+            {
+                // for local tiles, query the source directly since trivial blocking
+                //
+                tileImage = [_tileSource imageForTile:RMTileMake(x, y, zoom) inCache:[_mapView tileCache]];
+            }
+            else
             {
-                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void)
+                // for non-local tiles, consult cache directly first, else fetch asynchronously
+                //
+                tileImage = [[_mapView tileCache] cachedImage:RMTileMake(x, y, zoom) withCacheKey:[_tileSource uniqueTilecacheKey]];
+
+                if ( ! tileImage)
                 {
-                    if ([_tileSource imageForTile:RMTileMake(x, y, zoom) inCache:[_mapView tileCache]])
+                    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void)
                     {
-                        dispatch_async(dispatch_get_main_queue(), ^(void)
+                        if ([_tileSource imageForTile:RMTileMake(x, y, zoom) inCache:[_mapView tileCache]])
                         {
-                            [self.layer setNeedsDisplay];
-                        });
-                    }
-                });
+                            dispatch_async(dispatch_get_main_queue(), ^(void)
+                            {
+                                [self.layer setNeedsDisplay];
+                            });
+                        }
+                    });
+                }
             }
         }