duplicate point on cmd+d (#1831)

src/actions/actionDuplicateSelection.tsx

@@ -8,10 +8,47 @@ import { ToolButton } from "../components/ToolButton";
 import { clone } from "../components/icons";
 import { t } from "../i18n";
 import { getShortcutKey } from "../utils";
+import { LinearElementEditor } from "../element/linearElementEditor";
+import { mutateElement } from "../element/mutateElement";
 
 export const actionDuplicateSelection = register({
   name: "duplicateSelection",
   perform: (elements, appState) => {
+    // duplicate point if selected while editing multi-point element
+    if (appState.editingLinearElement) {
+      const { activePointIndex, elementId } = appState.editingLinearElement;
+      const element = LinearElementEditor.getElement(elementId);
+      if (!element || activePointIndex === null) {
+        return false;
+      }
+      const { points } = element;
+      const selectedPoint = points[activePointIndex];
+      const nextPoint = points[activePointIndex + 1];
+      mutateElement(element, {
+        points: [
+          ...points.slice(0, activePointIndex + 1),
+          nextPoint
+            ? [
+                (selectedPoint[0] + nextPoint[0]) / 2,
+                (selectedPoint[1] + nextPoint[1]) / 2,
+              ]
+            : [selectedPoint[0] + 30, selectedPoint[1] + 30],
+          ...points.slice(activePointIndex + 1),
+        ],
+      });
+      return {
+        appState: {
+          ...appState,
+          editingLinearElement: {
+            ...appState.editingLinearElement,
+            activePointIndex: activePointIndex + 1,
+          },
+        },
+        elements,
+        commitToHistory: true,
+      };
+    }
+
     const groupIdMap = new Map();
     return {
       appState,

src/actions/types.ts

@@ -2,12 +2,15 @@ import React from "react";
 import { ExcalidrawElement } from "../element/types";
 import { AppState } from "../types";
 
-export type ActionResult = {
-  elements?: readonly ExcalidrawElement[] | null;
-  appState?: AppState | null;
-  commitToHistory: boolean;
-  syncHistory?: boolean;
-};
+/** if false, the action should be prevented */
+export type ActionResult =
+  | {
+      elements?: readonly ExcalidrawElement[] | null;
+      appState?: AppState | null;
+      commitToHistory: boolean;
+      syncHistory?: boolean;
+    }
+  | false;
 
 type ActionFn = (
   elements: readonly ExcalidrawElement[],