3 files changed, 32 insertions, 13 deletions

diff --git a/src/client/views/InkControlPtHandles.tsx b/src/client/views/InkControlPtHandles.tsx
index df803ba31..a91e74c44 100644
--- a/src/client/views/InkControlPtHandles.tsx
+++ b/src/client/views/InkControlPtHandles.tsx
@@ -102,7 +102,7 @@ export class InkControlPtHandles extends React.Component<InkControlProps> {
     @action
     onDelete = (e: KeyboardEvent) => {
         if (["-", "Backspace", "Delete"].includes(e.key)) {
-            InkStrokeProperties.Instance?.deletePoints(this.props.inkView);
+            InkStrokeProperties.Instance?.deletePoints(this.props.inkView, e.shiftKey);
             e.stopPropagation();
         }
     }
diff --git a/src/client/views/InkStrokeProperties.ts b/src/client/views/InkStrokeProperties.ts
index 8ad4864f9..4808bbc77 100644
--- a/src/client/views/InkStrokeProperties.ts
+++ b/src/client/views/InkStrokeProperties.ts
@@ -1,16 +1,18 @@
 import { Bezier } from "bezier-js";
 import { action, observable, reaction } from "mobx";
-import { Doc, Opt, DocListCast } from "../../fields/Doc";
+import { Doc, NumListCast, Opt } from "../../fields/Doc";
 import { InkData, InkField, InkTool, PointData } from "../../fields/InkField";
 import { List } from "../../fields/List";
 import { listSpec } from "../../fields/Schema";
 import { Cast, NumCast } from "../../fields/Types";
+import { Point } from "../../pen-gestures/ndollar";
 import { DocumentType } from "../documents/DocumentTypes";
+import { FitOneCurve } from "../util/bezierFit";
 import { CurrentUserUtils } from "../util/CurrentUserUtils";
+import { DocumentManager } from "../util/DocumentManager";
 import { undoBatch } from "../util/UndoManager";
 import { InkingStroke } from "./InkingStroke";
 import { DocumentView } from "./nodes/DocumentView";
-import { DocumentManager } from "../util/DocumentManager";
 
 export class InkStrokeProperties {
     static Instance: InkStrokeProperties | undefined;
@@ -139,18 +141,35 @@ export class InkStrokeProperties {
      */
     @undoBatch
     @action
-    deletePoints = (inkView: DocumentView) => this.applyFunction(inkView, (view: DocumentView, ink: InkData) => {
+    deletePoints = (inkView: DocumentView, preserve: boolean) => this.applyFunction(inkView, (view: DocumentView, ink: InkData) => {
         const doc = view.rootDoc;
-        const newPoints: { X: number, Y: number }[] = [];
-        const toRemove = Math.floor((this._currentPoint + 2) / 4);
-        const last = this._currentPoint === ink.length - 1;
-        for (let i = 0; i < ink.length; i++) {
-            if (Math.floor((i + 2) / 4) !== toRemove && (toRemove !== 0 || i > 3)) {
-                newPoints.push({ X: ink[i].X, Y: ink[i].Y });
+        const newPoints = ink.slice();
+        const brokenIndices = NumListCast(doc.brokenInkIndices);
+        if (preserve || this._currentPoint === 0 || this._currentPoint === ink.length - 1 || brokenIndices.includes(this._currentPoint)) {
+            newPoints.splice(this._currentPoint === 0 ? 0 : this._currentPoint === ink.length - 1 ? this._currentPoint - 3 : this._currentPoint - 2, 4);
+        } else {
+            const start = this._currentPoint === 0 ? 0 : this._currentPoint - 4;
+            const splicedPoints = ink.slice(start, start + (this._currentPoint === 0 || this._currentPoint === ink.length - 1 ? 4 : 8));
+            var samples: Point[] = [];
+            var startDir = { x: 0, y: 0 };
+            var endDir = { x: 0, y: 0 };
+            for (var i = 0; i < splicedPoints.length / 4; i++) {
+                var bez = new Bezier(splicedPoints.slice(i * 4, i * 4 + 4).map(p => ({ x: p.X, y: p.Y })));
+                if (i === 0) startDir = bez.derivative(0);
+                if (i === splicedPoints.length / 4 - 1) endDir = bez.derivative(1);
+                for (var t = 0; t < (i === splicedPoints.length / 4 - 1 ? 1 + 1e-7 : 1); t += 0.05) {
+                    var pt = bez.compute(t);
+                    samples.push(new Point(pt.x, pt.y));
+                }
+            }
+            const { finalCtrls, error } = FitOneCurve(samples, { X: startDir.x, Y: startDir.y }, { X: endDir.x, Y: endDir.y });
+            if (error < 100) {
+                newPoints.splice(this._currentPoint - 4, 8, ...finalCtrls);
+            } else {
+                newPoints.splice(this._currentPoint - 2, 4);
             }
         }
-        doc.brokenInkIndices = new List(Cast(doc.brokenInkIndices, listSpec("number"), []).map(control => control >= toRemove * 4 ? control - 4 : control));
-        if (last) newPoints.splice(newPoints.length - 3, 2);
+        doc.brokenInkIndices = new List(brokenIndices.map(control => control >= this._currentPoint ? control - 4 : control));
         this._currentPoint = -1;
         return newPoints.length < 4 ? undefined : newPoints;
     }, true)
diff --git a/src/client/views/InkingStroke.tsx b/src/client/views/InkingStroke.tsx
index ecc82a580..8ff080f81 100644
--- a/src/client/views/InkingStroke.tsx
+++ b/src/client/views/InkingStroke.tsx
@@ -132,7 +132,7 @@ export class InkingStroke extends ViewBoxBaseComponent<FieldViewProps, InkDocume
                     } else if (isEditing) {
                         this._nearestT && this._nearestSeg !== undefined && InkStrokeProperties.Instance?.addPoints(this.props.docViewPath().lastElement(), this._nearestT, this._nearestSeg, this.inkScaledData().inkData.slice());
                     }
-                }), isEditing, isEditing, () => wasSelected && InkStrokeProperties.Instance && (InkStrokeProperties.Instance._currentPoint = -1));
+                }), isEditing, isEditing, action(() => wasSelected && InkStrokeProperties.Instance && (InkStrokeProperties.Instance._currentPoint = -1)));
         }
     }