Preview generator: generating a preview by layer number

preview_generator/parts/rows.js

@@ -1,4 +1,5 @@
 const HALVES_GAP = 5
+const NUMBER_OF_ROWS = 8
 
 const row = (keys, start, gapOffset) => [
   {x: start},
@@ -15,13 +16,22 @@ const row4 = (keys, rowIndex) => ({
   5: row(keys, 4, 0),
   6: row(keys, 6, -4),
   7: row(keys, 6, -4),
-}[rowIndex % 8])
+}[rowIndex % NUMBER_OF_ROWS])
 
 const buildRow = (keys, rowIndex) => ({
   12: row12(keys),
   4: row4(keys, rowIndex)
 }[keys.length] || ['Oh no...'])
 
+const layerRange = layerIndex =>
+  layerIndex === -1
+    ? []
+    : Array(2)
+      .fill(layerIndex)
+      .map((x, i) => x + i)
+      .map(x => x * NUMBER_OF_ROWS)
+
 module.exports = {
+  layerRange,
   buildRow
 }