fix getMarkersAverage edge case with small arrays

src/mol-geo/geometry/_spec/marker.spec.ts

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2021 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ *
+ * @author Alexander Rose <alexander.rose@weirdbyte.de>
+ */
+
+import { getMarkersAverage } from '../marker-data';
+
+describe('marker-data', () => {
+    it('getMarkersAverage', () => {
+        expect(getMarkersAverage(new Uint8Array([0, 0, 0, 0]), 3)).toBe(0);
+        expect(getMarkersAverage(new Uint8Array([0, 0, 1, 0]), 3)).toBe(1 / 3);
+        expect(getMarkersAverage(new Uint8Array([0, 0, 0, 0]), 4)).toBe(0);
+        expect(getMarkersAverage(new Uint8Array([0, 0, 1, 0]), 4)).toBe(1 / 4);
+    });
+});

src/mol-geo/geometry/marker-data.ts

@@ -47,12 +47,19 @@ export function getMarkersAverage(array: Uint8Array, count: number): number {
     const backStart = 4 * viewEnd;
 
     let sum = 0;
-    for (let i = 0; i < viewEnd; ++i) {
-        const v = view[i];
-        sum += MarkerCountLut[v & 0xFFFF] + MarkerCountLut[v >> 16];
-    }
-    for (let i = backStart; i < count; ++i) {
-        sum += array[i] && 1;
+    if (viewEnd < 0) {
+        // avoid edge cases with small arrays
+        for (let i = 0; i < count; ++i) {
+            sum += array[i] && 1;
+        }
+    } else {
+        for (let i = 0; i < viewEnd; ++i) {
+            const v = view[i];
+            sum += MarkerCountLut[v & 0xFFFF] + MarkerCountLut[v >> 16];
+        }
+        for (let i = backStart; i < count; ++i) {
+            sum += array[i] && 1;
+        }
     }
     return sum / count;
 }