Add new option to zoom sliding two fingers on OS X trackpad

It was requested here:
http://steamcommunity.com/app/431730/discussions/2/357286663677659387/

data/pref.xml

@@ -97,6 +97,7 @@
     </section>
     <section id="editor" text="Editor">
       <option id="zoom_with_wheel" type="bool" default="true" migrate="Options.ZoomWithMouseWheel" />
+      <option id="zoom_with_slide" type="bool" default="false" />
       <option id="zoom_from_center_with_wheel" type="bool" default="false" />
       <option id="zoom_from_center_with_keys" type="bool" default="false" />
       <option id="show_scrollbars" type="bool" default="true" migrate="Options.ShowScrollbars" />

data/widgets/options.xml

@@ -59,6 +59,7 @@
         <vbox id="section_editor">
           <separator text="Editor" horizontal="true" />
           <check text="Zoom with scroll wheel" id="wheel_zoom" />
+          <check text="Zoom sliding two fingers up or down" id="slide_zoom" />
           <check text="Zoom from center with scroll wheel" id="zoom_from_center_with_wheel" />
           <check text="Zoom from center with keys" id="zoom_from_center_with_keys" />
           <check text="Show scroll-bars in sprite editor" id="show_scrollbars" tooltip="Show scroll-bars in all sprite editors." />

src/app/commands/cmd_options.cpp

@@ -153,6 +153,13 @@ public:
     // Zoom with Scroll Wheel
     wheelZoom()->setSelected(m_pref.editor.zoomWithWheel());
 
+    // Zoom sliding two fingers
+#if __APPLE__
+    slideZoom()->setSelected(m_pref.editor.zoomWithSlide());
+#else
+    slideZoom()->setVisible(false);
+#endif
+
     // Checked background size
     checkedBgSize()->addItem("16x16");
     checkedBgSize()->addItem("8x8");
@@ -214,6 +221,9 @@ public:
     m_pref.editor.zoomFromCenterWithKeys(zoomFromCenterWithKeys()->isSelected());
     m_pref.editor.showScrollbars(showScrollbars()->isSelected());
     m_pref.editor.zoomWithWheel(wheelZoom()->isSelected());
+#if __APPLE__
+    m_pref.editor.zoomWithSlide(slideZoom()->isSelected());
+#endif
     m_pref.editor.rightClickMode(static_cast<app::gen::RightClickMode>(rightClickBehavior()->getSelectedItemIndex()));
     m_pref.editor.cursorColor(m_cursorColor->getColor());
     m_pref.editor.brushPreview(static_cast<app::gen::BrushPreview>(brushPreview()->getSelectedItemIndex()));

src/app/ui/editor/state_with_wheel_behavior.cpp

@@ -36,7 +36,8 @@ enum WHEEL_ACTION { WHEEL_NONE,
 
 bool StateWithWheelBehavior::onMouseWheel(Editor* editor, MouseMessage* msg)
 {
-  double dz = msg->wheelDelta().x + msg->wheelDelta().y;
+  gfx::Point delta = msg->wheelDelta();
+  double dz = delta.x + delta.y;
   WHEEL_ACTION wheelAction = WHEEL_NONE;
   bool scrollBigSteps = false;
 
@@ -50,21 +51,40 @@ bool StateWithWheelBehavior::onMouseWheel(Editor* editor, MouseMessage* msg)
   // Normal behavior: mouse wheel zooms If the message is from a
   // precise wheel i.e. a trackpad/touch-like device, we scroll by
   // default.
-  else if (Preferences::instance().editor.zoomWithWheel() &&
-           !msg->preciseWheel()) {
+  else if (Preferences::instance().editor.zoomWithWheel() && !msg->preciseWheel()) {
     if (msg->ctrlPressed())
       wheelAction = WHEEL_FRAME;
-    else if (msg->wheelDelta().x != 0 || msg->shiftPressed())
+    else if (delta.x != 0 || msg->shiftPressed())
       wheelAction = WHEEL_HSCROLL;
     else
       wheelAction = WHEEL_ZOOM;
   }
+  // Zoom sliding two fingers
+  else if (Preferences::instance().editor.zoomWithSlide() && msg->preciseWheel()) {
+    if (msg->ctrlPressed())
+      wheelAction = WHEEL_FRAME;
+    else if (std::abs(delta.x) > std::abs(delta.y)) {
+      delta.y = 0;
+      dz = delta.x;
+      wheelAction = WHEEL_HSCROLL;
+    }
+    else if (msg->shiftPressed()) {
+      delta.x = 0;
+      dz = delta.y;
+      wheelAction = WHEEL_VSCROLL;
+    }
+    else {
+      delta.x = 0;
+      dz = delta.y;
+      wheelAction = WHEEL_ZOOM;
+    }
+  }
   // For laptops, it's convenient to that Ctrl+wheel zoom (because
   // it's the "pinch" gesture).
   else {
     if (msg->ctrlPressed())
       wheelAction = WHEEL_ZOOM;
-    else if (msg->wheelDelta().x != 0 || msg->shiftPressed())
+    else if (delta.x != 0 || msg->shiftPressed())
       wheelAction = WHEEL_HSCROLL;
     else
       wheelAction = WHEEL_VSCROLL;
@@ -131,12 +151,8 @@ bool StateWithWheelBehavior::onMouseWheel(Editor* editor, MouseMessage* msg)
     case WHEEL_VSCROLL: {
       View* view = View::getView(editor);
       gfx::Point scroll = view->viewScroll();
-      gfx::Point delta(0, 0);
 
-      if (msg->preciseWheel()) {
-        delta = msg->wheelDelta();
-      }
-      else {
+      if (!msg->preciseWheel()) {
         gfx::Rect vp = view->viewportBounds();
 
         if (wheelAction == WHEEL_HSCROLL) {