Add blank, branching renderers

app/src/tiles/renderers/blankRenderer.ts

@@ -0,0 +1,21 @@
+import { Image } from "mapnik";
+import sharp from 'sharp';
+
+import { TileParams, TileRenderer } from "../types";
+
+class BlankRenderer implements TileRenderer {
+    getTile(tileParams: TileParams): Promise<Image> {
+        return sharp({
+            create: {
+                width: 1,
+                height: 1,
+                channels: 4,
+                background: { r: 0, g: 0, b: 0, alpha: 0 }
+            }
+        }).png().toBuffer();
+    }
+}
+
+export {
+    BlankRenderer
+};

app/src/tiles/renderers/branchingRenderer.ts

@@ -0,0 +1,23 @@
+import { Image } from "mapnik";
+
+import { TileParams, TileRenderer } from "../types";
+
+class BranchingRenderer {
+    constructor(
+        public branchTestFn: (tileParams: TileParams) => boolean,
+        public trueResultTileRenderer: TileRenderer,
+        public falseResultTileRenderer: TileRenderer
+    ) {}
+
+    getTile(tileParams: TileParams, dataParams: any): Promise<Image> {
+        if(this.branchTestFn(tileParams)) {
+            return this.trueResultTileRenderer.getTile(tileParams, dataParams);
+        } else {
+            return this.falseResultTileRenderer.getTile(tileParams, dataParams);
+        }
+    }
+}
+
+export {
+    BranchingRenderer
+};