Fix touch scaling for high dpi windows.

Touch events in windows are always expressed in screen coordinates, even if
the target app is not dpi-aware. This patch determines the dpi scale used
by the OS, and re-scales touch events accordingly. 

In some cases the touch events are sent to the wrong window. This is detected
and corrected.

BUG=175542


Review URL: https://chromiumcodereview.appspot.com/12317157

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@185474 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 55 insertions, 0 deletions

diff --git a/ui/base/win/dpi.cc b/ui/base/win/dpi.cc
index ecfb3e7..222b61f 100644
--- a/ui/base/win/dpi.cc
+++ b/ui/base/win/dpi.cc
@@ -7,6 +7,7 @@
 #include <windows.h>
 
 #include "base/win/scoped_hdc.h"
+#include "base/win/registry.h"
 #include "ui/gfx/display.h"
 #include "ui/gfx/point_conversions.h"
 #include "ui/gfx/rect_conversions.h"
@@ -27,6 +28,16 @@ float GetDeviceScaleFactorImpl() {
 #endif
 }
 
+BOOL IsProcessDPIAwareWrapper() {
+  typedef BOOL(WINAPI *IsProcessDPIAwarePtr)(VOID);
+  IsProcessDPIAwarePtr is_process_dpi_aware_func =
+      reinterpret_cast<IsProcessDPIAwarePtr>(
+          GetProcAddress(GetModuleHandleA("user32.dll"), "IsProcessDPIAware"));
+  if (is_process_dpi_aware_func)
+    return is_process_dpi_aware_func();
+  return FALSE;
+}
+
 }  // namespace
 
 namespace ui {
@@ -100,6 +111,28 @@ gfx::Size DIPToScreenSize(const gfx::Size& dip_size) {
   return gfx::ToFlooredSize(gfx::ScaleSize(dip_size, GetDeviceScaleFactor()));
 }
 
+double GetDPIScaleFromRegistry() {
+  static double scale = -1.0;
+  if (scale == -1.0) {
+    double result = 1.0;
+    if (!IsProcessDPIAwareWrapper()) {
+      //HKEY_CURRENT_USER\Control Panel\Desktop\WindowMetrics\AppliedDPI
+      base::win::RegKey key(HKEY_CURRENT_USER,
+                            L"Control Panel\\Desktop\\WindowMetrics",
+                            KEY_QUERY_VALUE);
+
+      if (key.Valid()) {
+        DWORD value = 0;
+        if (key.ReadValueDW(L"AppliedDPI", &value) == ERROR_SUCCESS) {
+          result = ((double)value) / kDefaultDPIX;
+        }
+      }
+    }
+    scale = result;
+  }
+  return scale;
+}
+
 }  // namespace win
 
 }  // namespace ui
diff --git a/ui/base/win/dpi.h b/ui/base/win/dpi.h
index 99252c7..a33e0ab 100644
--- a/ui/base/win/dpi.h
+++ b/ui/base/win/dpi.h
@@ -38,6 +38,8 @@ UI_EXPORT gfx::Size ScreenToDIPSize(const gfx::Size& size_in_pixels);
 
 UI_EXPORT gfx::Size DIPToScreenSize(const gfx::Size& dip_size);
 
+UI_EXPORT double GetDPIScaleFromRegistry();
+
 }  // namespace win
 
 }  // namespace ui
diff --git a/ui/base/win/hwnd_subclass.cc b/ui/base/win/hwnd_subclass.cc
index 94ab44c..c8102a2 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))) {
+      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;