Implemented smooth scrolling using xinput2 in X11.

chrome/browser/ui/views/frame/browser_root_view.cc

Index: chrome/browser/ui/views/frame/browser_root_view.cc
diff --git a/chrome/browser/ui/views/frame/browser_root_view.cc b/chrome/browser/ui/views/frame/browser_root_view.cc
index 8eaba179f86a695221aa7829c3ef50b382a47018..9057a6df1492c6830fbc7c2714bd98d5438ffaab 100644
--- a/chrome/browser/ui/views/frame/browser_root_view.cc
+++ b/chrome/browser/ui/views/frame/browser_root_view.cc
@@ -28,7 +28,9 @@ BrowserRootView::BrowserRootView(BrowserView* browser_view,
                                  views::Widget* widget)
     : views::internal::RootView(widget),
       browser_view_(browser_view),
-      forwarding_to_tab_strip_(false) { }
+      forwarding_to_tab_strip_(false),
+      scroll_amount_x_(0),
+      scroll_amount_y_(0) {}
 
 bool BrowserRootView::GetDropFormats(
       int* formats,
@@ -130,19 +132,39 @@ bool BrowserRootView::OnMouseWheel(const ui::MouseWheelEvent& event) {
     if (tabstrip()->Contains(hit_view) ||
         hittest == HTCAPTION ||
         hittest == HTTOP) {
-      int scroll_offset = abs(event.y_offset()) > abs(event.x_offset()) ?
-          event.y_offset() : event.x_offset();
+      scroll_amount_x_ += event.x_offset();
+      scroll_amount_y_ += event.y_offset();
+      int scroll_offset = abs(scroll_amount_y_) > abs(scroll_amount_x_)
+                              ? scroll_amount_y_
+                              : scroll_amount_x_;
+
+      // Number of integer scroll events that have passed
+      int whole_scroll_offset = round((double)scroll_offset /
+                                      (double)ui::MouseWheelEvent::kWheelDelta);
+
+      if (whole_scroll_offset != 0) {
+        // Re-adjust back towards 0
+        if (abs(scroll_amount_y_) > abs(scroll_amount_x_)) {
+          scroll_amount_y_ -=
+              whole_scroll_offset * ui::MouseWheelEvent::kWheelDelta;
+        } else {
+          scroll_amount_x_ -=
+              whole_scroll_offset * ui::MouseWheelEvent::kWheelDelta;
+        }
+      }
+
       Browser* browser = browser_view_->browser();
       TabStripModel* model = browser->tab_strip_model();
       // Switch to the next tab only if not at the end of the tab-strip.
-      if (scroll_offset < 0 && model->active_index() + 1 < model->count()) {
+      if (whole_scroll_offset < 0 &&
+          model->active_index() + 1 < model->count()) {
         chrome::SelectNextTab(browser);
         return true;
       }
 
       // Switch to the previous tab only if not at the beginning of the
       // tab-strip.
-      if (scroll_offset > 0 && model->active_index() > 0) {
+      if (whole_scroll_offset > 0 && model->active_index() > 0) {
         chrome::SelectPreviousTab(browser);
         return true;
       }

[sadrul, 2016/01/04 18:51:21]

Is this code equivalent to:

  scroll_amount_x_ += ...;
  scroll_amount_y_ += ...;
  int scroll_offset = ...;

  scroll_amount_x_ %= kWheelDelta;
  scroll_amount_y_ %= kWheelDelta;

  Browser* browser = ...;
  TabStripModel* model = ...;
  bool switch_next = scroll_offset <= -kWheelDelta;
  bool switch_prev = scroll_offset >= kWheelDelta;
  if (switch_next && mode->active_index() + 1 < model->count()) {
    chrome::SelectNextTab(browser);
    return true;
  } else if (switch_prev && model->active_index() > 0) {
    chrome::SelectPreviousTab(browser);
    return true;
  }

? Because I think that's much easier to understand.

[Will Shackleton, 2016/01/04 21:07:41]

Unfortunately the modulo operator doesn't give the correct behaviour; from a
quick glance around the sign of a%b where a is negative is implementation
defined, and secondly by using round we actually change tab half way through a
traditional scroll event; for example, for a mouse with a high resolution
scrollwheel that still has quantised "clicks" (such as the Performance MX mouse)
one would expect the tab to change halfway through the scroll, not right at the
beginning.

I can certainly clean up the if statement a bit.

@@ -151,6 +173,13 @@ bool BrowserRootView::OnMouseWheel(const ui::MouseWheelEvent& event) {
   return RootView::OnMouseWheel(event);
 }
 
+void BrowserRootView::OnMouseExited(const ui::MouseEvent& event) {
+  // Reset such that the tab switch always occurs halfway through a smooth
+  // scroll
+  scroll_amount_x_ = 0;
+  scroll_amount_y_ = 0;
+}
+
 void BrowserRootView::OnEventProcessingStarted(ui::Event* event) {
   if (event->IsGestureEvent()) {
     ui::GestureEvent* gesture_event = event->AsGestureEvent();