Fix touch scaling for high dpi windows.

ui/base/win/hwnd_subclass.cc

Index: ui/base/win/hwnd_subclass.cc
diff --git a/ui/base/win/hwnd_subclass.cc b/ui/base/win/hwnd_subclass.cc
index 94ab44cf7034af1bf261bfa4be874614f3357baa..c8102a2060dcfbdc1cb1e8f3685203014d473531 100644
--- a/ui/base/win/hwnd_subclass.cc
+++ b/ui/base/win/hwnd_subclass.cc
@@ -9,6 +9,7 @@
 #include "base/logging.h"
 #include "base/memory/scoped_vector.h"
 #include "base/memory/singleton.h"
+#include "ui/base/win/dpi.h"
 #include "ui/base/win/hwnd_util.h"
 
 namespace {
@@ -119,6 +120,25 @@ LRESULT HWNDSubclass::OnWndProc(HWND hwnd,
                                 UINT message,
                                 WPARAM w_param,
                                 LPARAM l_param) {
+
+  // Touch messages are always passed in screen coordinates. If the OS is
+  // scaled, but the app is not DPI aware, then then WM_TOUCH might be
+  // intended for a different window.
+  if (message == WM_TOUCH) {
+    TOUCHINPUT point;
+
+    if (GetTouchInputInfo((HTOUCHINPUT)l_param, 1,
+                                     &point, sizeof(TOUCHINPUT))) {

[Ryan Sleevi, 2013/03/05 18:32:56]

style: indentation
BUG: GetTouchInputInfo is only available on Win7+. You need to
GetProcAdress-wrap this function

+      POINT touch_location = {
+          TOUCH_COORD_TO_PIXEL(point.x) / ui::win::GetDPIScaleFromRegistry(),
+          TOUCH_COORD_TO_PIXEL(point.y) / ui::win::GetDPIScaleFromRegistry()};
+      HWND actual_target = WindowFromPoint(touch_location);
+      if (actual_target != hwnd) {
+        return SendMessage(actual_target, message, w_param, l_param);
+      }
+    }
+  }
+
   for (std::vector<HWNDMessageFilter*>::iterator it = filters_.begin();
       it != filters_.end(); ++it) {
     LRESULT l_result = 0;