Remove unfinished polygon when undoing and redoing in IO mode (#3759)

* make removeUnfinishedPolygon return whether a polygon was removed

* treat removing an unfinished polygon as a discrete undo step

* has to be handled when redoing as well, but not as a discrete step

ts/routes/image-occlusion/tools/tool-polygon.ts

@@ -235,7 +235,15 @@ export const modifiedPolygon = (canvas: fabric.Canvas, polygon: fabric.Polygon):
     canvas.add(polygon1);
 };
 
-export const removeUnfinishedPolygon = (canvas: fabric.Canvas): void => {
+/**
+ * Removes the currently unfinished polygon, if any, and reset internal state
+ * @returns whether or not such a polygon was removed and state was reset
+ */
+export const removeUnfinishedPolygon = (canvas: fabric.Canvas): boolean => {
+    if (!activeShape) {
+        // generatePolygon should've already removed points/lines and reset state
+        return false;
+    }
     canvas.remove(activeShape).remove(activeLine);
     pointsList.forEach((point) => {
         canvas.remove(point);
@@ -249,4 +257,5 @@ export const removeUnfinishedPolygon = (canvas: fabric.Canvas): void => {
     pointsList = [];
     drawMode = false;
     canvas.selection = true;
+    return true;
 };

ts/routes/image-occlusion/tools/tool-undo-redo.ts

@@ -9,6 +9,7 @@ import { mdiRedo, mdiUndo } from "$lib/components/icons";
 
 import { saveNeededStore } from "../store";
 import { redoKeyCombination, undoKeyCombination } from "./shortcuts";
+import { removeUnfinishedPolygon } from "./tool-polygon";
 
 /**
  * Undo redo for rectangle and ellipse handled here,
@@ -126,6 +127,10 @@ class UndoStack {
     }
 
     undo(): void {
+        if (this.canvas && removeUnfinishedPolygon(this.canvas)) {
+            // treat removing the unfinished polygon as an undo step
+            return;
+        }
         if (this.canUndo()) {
             this.index--;
             this.updateState();
@@ -134,6 +139,10 @@ class UndoStack {
     }
 
     redo(): void {
+        if (this.canvas) {
+            // when redoing, removing an unfinished polygon doesn't make sense as a discrete step
+            removeUnfinishedPolygon(this.canvas);
+        }
         if (this.canRedo()) {
             this.index++;
             this.updateState();