Mapsforge: at large query zoom levels enlarge clip buffer, fixes #231

docs/Changelog.md

@@ -5,6 +5,7 @@
 - Mapsforge themes compatibility [#100](https://github.com/mapsforge/vtm/issues/100)
 - Render themes: line symbol [#124](https://github.com/mapsforge/vtm/issues/124)
 - Render themes: stroke dash array [#131](https://github.com/mapsforge/vtm/issues/131)
+- Mapsforge fix artifacts for zoom > 17 [#231](https://github.com/mapsforge/vtm/issues/231)
 - vtm-theme-comparator module [#387](https://github.com/mapsforge/vtm/issues/387)
 - Many other minor improvements and bug fixes
 - [Solved issues](https://github.com/mapsforge/vtm/issues?q=is%3Aclosed+milestone%3A0.9.0)

vtm/src/org/oscim/tiling/source/mapfile/MapDatabase.java

@@ -372,8 +372,12 @@ public class MapDatabase implements ITileDataSource {
 
         //log.debug(numCols + "/" + numRows + " " + mCurrentCol + " " + mCurrentRow);
 
-        // Buffer based on dpi
-        int buffer = (int) (16 * CanvasAdapter.dpi / CanvasAdapter.DEFAULT_DPI + 0.5f);
+        // At large query zoom levels use enlarged buffer
+        int buffer;
+        if (queryParameters.queryZoomLevel > MapFileTileSource.MAX_ZOOM_LEVEL)
+            buffer = Tile.SIZE / 2;
+        else
+            buffer = (int) (16 * CanvasAdapter.dpi / CanvasAdapter.DEFAULT_DPI + 0.5f);
 
         xmin = -buffer;
         ymin = -buffer;