Get parents from FAMS in case they're not married

src/ancestor-chart.ts

@@ -80,11 +80,7 @@ export class AncestorChart<IndiT extends Indi, FamT extends Fam>
       if (!fam) {
         continue;
       }
-      const [father, mother] =
-        entry.family!.id === this.options.startFam &&
-        this.options.swapStartSpouses
-          ? [fam.getMother(), fam.getFather()]
-          : [fam.getFather(), fam.getMother()];
+      const [father, mother] = this.getParents(fam, entry);
       if (!father && !mother) {
         continue;
       }
@@ -134,4 +130,29 @@ export class AncestorChart<IndiT extends Indi, FamT extends Fam>
     this.util.updateSvgDimensions(info);
     return Object.assign(info, { animationPromise });
   }
+
+  private getParents(fam: Fam, entry: TreeNode) {
+    let [father, mother] = [fam.getFather(), fam.getMother()];
+    if(!father && !mother) {
+      // get indis whose FAMS contains this family
+      const res: any[] = Array.from((this.options.data as any).indis.entries())
+          .filter((e: any[]) => e[1]?.json?.fams && e[1].json.fams.includes(entry.family?.id));
+      const getFromRes = function(pRes: any, sex: "M" | "F") {
+        const r = pRes.find((e: any) => e[1].json.sex === sex);
+        return r.length === 2
+            ? r[1].json?.id || null
+            : null;
+      }
+      father = getFromRes(res, "M");
+      mother = getFromRes(res, "F");
+    }
+
+    if(this.options.swapStartSpouses) {
+      const pivot = father;
+      father = mother;
+      mother = pivot;
+    }
+
+    return [father || null, mother || null];
+  }
 }

tests/ancestor-chart.spec.ts

@@ -56,10 +56,36 @@ describe('Ancestor chart', () => {
     const data = new JsonDataProvider(json);
     const chart = new AncestorChart({
       data,
-      startFam: 'F1',
+      startFam: json.fams[0].id,
       renderer: new FakeRenderer(),
       svgSelector: 'svg',
     });
     chart.render();
   });
+
+  it('should work with FAM values only', () => {
+    // I1+I2
+    //   F1
+    //   |
+    //   I3
+    const json: JsonGedcomData = {
+      fams: [
+        {id: 'F1', children: []},
+      ],
+      indis: [
+        {id: 'I1', fams: ['F1'], sex: "M"},
+        {id: 'I2', fams: ['F1'], sex: "F"},
+        {id: 'I3', famc: 'F1', sex: "F"},
+      ],
+    };
+    const data = new JsonDataProvider(json);
+    const chart = new AncestorChart({
+      data,
+      startFam: json.fams[0].id,
+      renderer: new FakeRenderer(),
+      svgSelector: 'svg',
+    });
+    chart.render();
+  });
+
 });