Tidy up object count handling

src/drawables/drawable-descriptor.ts

@@ -47,6 +47,15 @@ export interface DrawableDescriptor {
     isInverted?: boolean;
   };
 
+  /**
+   * Calculating the number of objects to be drawn is done using the following pseudo-formula:
+   *
+   * objectCountScaler * propertyUniformMapping[0].length
+   *
+   * By default, its value is 1
+   */
+  objectCountScaler?: number;
+
   /**
    * Number of possible drawables around each tile.
    *