Add an option to scale the tile size.

In ractice, only MVT is interested in this, but because
of how the paint area is set up it needed to be more
generic.

src/extension/vectortiles/src/main/java/org/geoserver/wms/mapbox/MapBoxTileBuilderFactory.java

@@ -33,4 +33,32 @@ public String getMimeType() {
     public MapBoxTileBuilder newBuilder(Rectangle screenSize, ReferencedEnvelope mapArea) {
         return new MapBoxTileBuilder(screenSize, mapArea);
     }
+
+    /**
+     * For Mapbox tiles, since they are rendered in screen/tile space, oversampling produces more
+     * consistent results when zooming. See this question here:
+     *
+     * <p>https://github.com/mapbox/vector-tiles/issues/45
+     *
+     * @return
+     */
+    @Override
+    public boolean shouldOversampleScale() {
+        return true;
+    }
+
+    /**
+     * Use 16x oversampling to match actual Mapbox tile extent, which is 4096 for 900913 tiles
+     *
+     * @return
+     */
+    @Override
+    public int getOversampleX() {
+        return 16;
+    }
+
+    @Override
+    public int getOversampleY() {
+        return 16;
+    }
 }

src/extension/vectortiles/src/main/java/org/geoserver/wms/vector/VectorTileBuilderFactory.java

@@ -26,4 +26,26 @@ public interface VectorTileBuilderFactory {
      * @param mapArea The extent of the tile in target CRS coordinates
      */
     VectorTileBuilder newBuilder(Rectangle screenSize, ReferencedEnvelope mapArea);
+
+    /**
+     * Whether tiles from this builder should be "oversampled", that is, "rendered" at a higher
+     * resolution than the tile resolution. The motivation for this is Mapbox vector tiles, which
+     * are rendered in screen space per tile and have inconsistent behavior while zooming at lower
+     * resolutions.
+     *
+     * @return whether this builder requires oversampling. defaults to false.
+     */
+    default boolean shouldOversampleScale() {
+        return false;
+    }
+
+    /** @return the horizontal oversampling factor. default is 1, no oversampling */
+    default int getOversampleX() {
+        return 1;
+    }
+
+    /** @return the vertical oversampling factor. default is 1, no oversampling */
+    default int getOversampleY() {
+        return 1;
+    }
 }

src/extension/vectortiles/src/main/java/org/geoserver/wms/vector/VectorTileMapOutputFormat.java

@@ -94,12 +94,16 @@ public WebMap produceMap(final WMSMapContent mapContent) throws ServiceException
         checkArgument(mapContent.getMapWidth() > 0);
         checkArgument(mapContent.getMapHeight() > 0);
 
-        // mapContent.setMapWidth(5 * mapContent.getMapWidth());
-        // mapContent.setMapHeight(5 * mapContent.getMapHeight());
-
         final ReferencedEnvelope renderingArea = mapContent.getRenderingArea();
-        final Rectangle paintArea =
-                new Rectangle(mapContent.getMapWidth(), mapContent.getMapHeight());
+        int mapWidth = mapContent.getMapWidth();
+        int mapHeight = mapContent.getMapHeight();
+        Rectangle paintArea = new Rectangle(mapWidth, mapHeight);
+        if (this.tileBuilderFactory.shouldOversampleScale()) {
+            paintArea =
+                    new Rectangle(
+                            this.tileBuilderFactory.getOversampleX() * mapWidth,
+                            this.tileBuilderFactory.getOversampleY() * mapHeight);
+        }
 
         VectorTileBuilder vectorTileBuilder;
         vectorTileBuilder = this.tileBuilderFactory.newBuilder(paintArea, renderingArea);

src/extension/vectortiles/src/test/java/org/geoserver/wms/vector/VectorTilesIntegrationTest.java

@@ -80,10 +80,9 @@ public void checkSimpleMVT(String mimeType) throws Exception {
         byte[] responseBytes = response.getContentAsByteArray();
         VectorTileDecoder decoder = new VectorTileDecoder();
         List<VectorTileDecoder.Feature> featuresList = decoder.decode(responseBytes).asList();
-        // MapBox encoder skips too small geometries
-        assertEquals(3, featuresList.size());
+        assertEquals(5, featuresList.size());
         assertEquals(
-                2,
+                3,
                 featuresList
                         .stream()
                         .filter(f -> "Route 5".equals(f.getAttributes().get("NAME")))
@@ -94,6 +93,7 @@ public void checkSimpleMVT(String mimeType) throws Exception {
                         .stream()
                         .filter(f -> "Main Street".equals(f.getAttributes().get("NAME")))
                         .count());
+        assertEquals("Extent should be 12288", 12288, featuresList.get(0).getExtent());
     }
 
     @Test