feat: add s-pen button erasing

lib/components/canvas/canvas_gesture_detector.dart

@@ -23,6 +23,7 @@ class CanvasGestureDetector extends StatefulWidget {
     required this.onDrawUpdate,
     required this.onDrawEnd,
     required this.onPressureChanged,
+    required this.onStylusButtonChanged,
 
     required this.undo,
     required this.redo,
@@ -45,6 +46,7 @@ class CanvasGestureDetector extends StatefulWidget {
   /// Called when the pressure of the stylus changes,
   /// pressure is negative if stylus button is pressed
   final ValueChanged<double?> onPressureChanged;
+  final ValueChanged<bool> onStylusButtonChanged;
 
   final VoidCallback undo;
   final VoidCallback redo;
@@ -202,15 +204,26 @@ class _CanvasGestureDetectorState extends State<CanvasGestureDetector> {
 
   void _listenerPointerEvent(PointerEvent event) {
     double? pressure;
+    bool stylusButtonPressed = false;
+
     if (event.kind == PointerDeviceKind.stylus) {
       pressure = event.pressure;
+      stylusButtonPressed = event.buttons == kPrimaryStylusButton;
     } else if (event.kind == PointerDeviceKind.invertedStylus) {
-      pressure = -event.pressure;
+      pressure = event.pressure;
+      stylusButtonPressed = true; // treat eraser as stylus button
     } else if (Platform.isLinux && event.pressureMin != event.pressureMax) {
       // if min == max, then the device isn't pressure sensitive
       pressure = event.pressure;
     }
+
     widget.onPressureChanged(pressure);
+    widget.onStylusButtonChanged(stylusButtonPressed);
+  }
+
+  void _listenerPointerUpEvent(PointerEvent event) {
+    widget.onPressureChanged(null);
+    widget.onStylusButtonChanged(false);
   }
 
   @override
@@ -222,6 +235,7 @@ class _CanvasGestureDetectorState extends State<CanvasGestureDetector> {
         Listener(
           onPointerDown: _listenerPointerEvent,
           onPointerMove: _listenerPointerEvent,
+          onPointerUp: _listenerPointerUpEvent,
           child: GestureDetector(
             onSecondaryTapUp: (TapUpDetails details) => widget.undo(),
             onTertiaryTapUp: (TapUpDetails details) => widget.redo(),

lib/components/toolbar/toolbar.dart

@@ -131,11 +131,7 @@ class _ToolbarState extends State<Toolbar> {
 
   void toggleEraser() {
     toolOptionsType = ToolOptions.hide;
-    if (widget.currentTool is Eraser) {
-      widget.setTool(Pen.currentPen);
-    } else {
-      widget.setTool(Eraser());
-    }
+    widget.setTool(Eraser()); // this toggles eraser
   }
   void toggleColorOptions() {
     setState(() {

lib/pages/editor/editor.dart

@@ -127,6 +127,11 @@ class EditorState extends State<Editor> {
   /// Whether the platform can rasterize a pdf
   bool canRasterPdf = true;
 
+  /// The tool that was used before switching to the eraser.
+  Tool? tmpTool;
+  /// If the stylus button is pressed.
+  bool stylusButtonPressed = false;
+
   @override
   void initState() {
     DynamicMaterialApp.addFullscreenListener(_setState);
@@ -466,8 +471,6 @@ class EditorState extends State<Editor> {
 
   int? dragPageIndex;
   double? currentPressure;
-  /// if [pressureWasNegative], switch back to pen when pressure becomes positive again
-  bool pressureWasNegative = false;
   bool isDrawGesture(ScaleStartDetails details) {
     if (coreInfo.readOnly) return false;
 
@@ -626,11 +629,6 @@ class EditorState extends State<Editor> {
       }
     });
     autosaveAfterDelay();
-
-    if (pressureWasNegative) {
-      pressureWasNegative = false;
-      currentTool = Pen.currentPen;
-    }
   }
   void onInteractionEnd(ScaleEndDetails details) {
     // reset after 1ms to keep track of the same gesture only
@@ -639,13 +637,27 @@ class EditorState extends State<Editor> {
       lastSeenPointerCount = 0;
     });
   }
-  void onPressureChanged(double? pressure) {
-    currentPressure = pressure == 0.0 ? null : pressure;
-    if (currentPressure == null) return;
 
-    if (currentPressure! < 0) {
-      pressureWasNegative = true;
+  void onPressureChanged(double? pressure) {
+    currentPressure = pressure == 0 ? null : pressure;
+  }
+  void onStylusButtonChanged(bool buttonPressed) {
+    stylusButtonPressed = buttonPressed;
+
+    if (buttonPressed) {
+      if (currentTool is Eraser) return;
+      tmpTool = currentTool;
+      if (currentTool is Pen && dragPageIndex != null) {
+        // if the pen is currently drawing, end the stroke
+        (currentTool as Pen).onDragEnd();
+      }
       currentTool = Eraser();
+      setState(() {});
+    } else {
+      if (tmpTool == null) return;
+      currentTool = tmpTool!;
+      tmpTool = null;
+      setState(() {});
     }
   }
 
@@ -1107,6 +1119,7 @@ class EditorState extends State<Editor> {
       onDrawStart: onDrawStart,
       onDrawUpdate: onDrawUpdate,
       onDrawEnd: onDrawEnd,
+      onStylusButtonChanged: onStylusButtonChanged,
       onPressureChanged: onPressureChanged,
 
       undo: undo,
@@ -1189,6 +1202,18 @@ class EditorState extends State<Editor> {
 
           setTool: (tool) {
             setState(() {
+              if (tool is Eraser) {
+                // setTool(Eraser) is called to toggle eraser
+                if (currentTool is Eraser && tmpTool != null) {
+                  // switch to previous tool
+                  tool = tmpTool!;
+                  tmpTool = null;
+                } else {
+                  // store previous tool to restore it later
+                  tmpTool = currentTool;
+                }
+              }
+
               currentTool = tool;
 
               if (currentTool is Highlighter) {