Make MouseInputEvent only consider one pressed button - discard any B…

…UTTON_PRESS while the first button is not released

src/core/gui/inputdevices/MouseInputHandler.cpp

@@ -34,7 +34,12 @@ auto MouseInputHandler::handleImpl(InputEvent const& event) -> bool {
      */
     // Trigger start of action when pen/mouse is pressed
     if (event.type == BUTTON_PRESS_EVENT) {
-        this->actionStart(event);
+        if (pressedButton == BUTTON_NONE || !inputRunning) {
+            pressedButton = event.button;
+            this->actionStart(event);
+        } else if (event.button == pressedButton) {
+            g_warning("MouseInputHandler: Double BUTTON_PRESS_EVENT on button %u", event.button);
+        }
         return true;
     }
 
@@ -67,13 +72,17 @@ auto MouseInputHandler::handleImpl(InputEvent const& event) -> bool {
 
     // Trigger end of action if mouse button is released
     if (event.type == BUTTON_RELEASE_EVENT) {
-        this->actionEnd(event);
+        if (event.button == pressedButton) {
+            pressedButton = BUTTON_NONE;
+            this->actionEnd(event);
+        }
         return true;
     }
 
     // If we loose our Grab on the device end the current action
     if (event.type == GRAB_BROKEN_EVENT && this->deviceClassPressed) {
         // TODO(fabian): We may need to update pressed state manually here
+        pressedButton = BUTTON_NONE;
         this->actionEnd(event);
         return true;
     }

src/core/gui/inputdevices/MouseInputHandler.h

@@ -11,6 +11,8 @@
 
 #pragma once
 
+#include <glib.h>  // for guint
+
 #include "PenInputHandler.h"  // for PenInputHandler
 
 class InputContext;
@@ -41,4 +43,9 @@ class MouseInputHandler: public PenInputHandler {
      */
     bool changeTool(InputEvent const& event) override;
     void onBlock() override;
+
+private:
+    // see button member in https://docs.gtk.org/gdk3/struct.EventButton.html
+    static constexpr guint BUTTON_NONE = 0;
+    guint pressedButton = BUTTON_NONE;
 };