Improve detection of one click when using a stylus

We can interpret a quick mouse down/up events (e.g. less than 250
milliseconds) as a simple click if the mouse doesn't move too much in
the middle of both events (e.g. a tiny rectangle of 7x7 pixels).

Some discussion about this: https://community.aseprite.org/t/12491/10

src/app/ui/editor/drawing_state.cpp

@@ -36,6 +36,9 @@
 #include "app/ui/main_window.h"
 #include "app/ui/timeline/timeline.h"
 
+#include <algorithm>
+#include <cmath>
+#include <cstdlib>
 #include <cstring>
 
 namespace app {
@@ -104,6 +107,9 @@ void DrawingState::initToolLoop(Editor* editor,
 
   m_velocity.reset();
   m_lastPointer = pointer;
+  m_mouseDownPos = msg->position();
+  m_mouseDownTime = base::current_tick();
+
   m_toolLoopManager->prepareLoop(pointer);
   m_toolLoopManager->pressButton(pointer);
 
@@ -193,7 +199,7 @@ bool DrawingState::onMouseUp(Editor* editor, MouseMessage* msg)
   // one click).
   if (!m_toolLoop->getInk()->isSelection() ||
       m_toolLoop->getController()->isOnePoint() ||
-      m_mouseMoveReceived ||
+      !canInterpretMouseMovementAsJustOneClick() ||
       // In case of double-click (to select tiles) we don't want to
       // deselect if the mouse is not moved. In this case the tile
       // will be selected anyway even if the mouse is not moved.
@@ -253,6 +259,9 @@ bool DrawingState::onMouseMove(Editor* editor, MouseMessage* msg)
   // (used in the Rectangular Marquee to deselect when we just do a
   // simple click without moving the mouse).
   m_mouseMoveReceived = true;
+  gfx::Point delta = (msg->position() - m_mouseDownPos);
+  m_mouseMaxDelta.x = std::max(m_mouseMaxDelta.x, std::abs(delta.x));
+  m_mouseMaxDelta.y = std::max(m_mouseMaxDelta.y, std::abs(delta.y));
 
   // Use DelayedMouseMove for tools like line, rectangle, etc. (that
   // use the only the last mouse position) to filter out rapid mouse
@@ -358,6 +367,18 @@ void DrawingState::handleMouseMovement()
   m_toolLoopManager->movement(m_lastPointer);
 }
 
+bool DrawingState::canInterpretMouseMovementAsJustOneClick()
+{
+  // If the user clicked (pressed and released the mouse button) in
+  // less than 250 milliseconds in "the same place" (inside a 7 pixels
+  // rectangle actually, to detect stylus shake).
+  return
+    !m_mouseMoveReceived ||
+    (m_mouseMaxDelta.x < 4 &&
+     m_mouseMaxDelta.y < 4 &&
+     (base::current_tick() - m_mouseDownTime < 250));
+}
+
 bool DrawingState::canExecuteCommands()
 {
   // Returning true here means that the user can trigger commands with

src/app/ui/editor/drawing_state.h

@@ -13,6 +13,7 @@
 #include "app/tools/velocity.h"
 #include "app/ui/editor/delayed_mouse_move.h"
 #include "app/ui/editor/standby_state.h"
+#include "base/time.h"
 #include "obs/connection.h"
 #include <memory>
 
@@ -58,6 +59,7 @@ namespace app {
 
   private:
     void handleMouseMovement();
+    bool canInterpretMouseMovementAsJustOneClick();
     bool canExecuteCommands();
     void onBeforeCommandExecution(CommandExecutionEvent& ev);
     void destroyLoopIfCanceled(Editor* editor);
@@ -77,10 +79,13 @@ namespace app {
     // Tool-loop manager
     std::unique_ptr<tools::ToolLoopManager> m_toolLoopManager;
 
-    // True if at least we've received a onMouseMove(). It's used to
+    // These fields are used to detect a selection tool cancelation
-    // cancel selection tool (deselect) when the user click (press and
+    // (deselect command) when the user just click (press and release
-    // release the mouse button in the same location).
+    // the mouse button in the "same location" approximately).
     bool m_mouseMoveReceived;
+    gfx::Point m_mouseMaxDelta;
+    gfx::Point m_mouseDownPos;
+    base::tick_t m_mouseDownTime;
 
     // Stores the last mouse pointer, used to re-use the latest mouse
     // button when onScrollChange() event is received.