Fix range of gamepad axis values on Windows

Previously was being normalized via division by 32767, but the range is documented to be -32768..32767 so we need to bias to not exceed -1..1 and get the full range.

Also inspected the Linux code expecting a similar bug, but the range there is documented to be -32767..32767 so simple division suffices.

R=rsleevi
BUG=119791


Review URL: http://codereview.chromium.org/9838078

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@128773 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 7 insertions, 5 deletions

diff --git a/content/browser/gamepad/platform_data_fetcher_win.cc b/content/browser/gamepad/platform_data_fetcher_win.cc
index 8c30264..ce07b5f 100644
--- a/content/browser/gamepad/platform_data_fetcher_win.cc
+++ b/content/browser/gamepad/platform_data_fetcher_win.cc
@@ -33,7 +33,9 @@ static const BYTE kDeviceSubTypeDrumKit = 8;
 static const BYTE kDeviceSubTypeGuitarBass = 11;
 static const BYTE kDeviceSubTypeArcadePad = 19;
 
-const float kMaxWinAxisValue = 32767.0;
+float NormalizeAxis(SHORT value) {
+  return ((value + 32768.f) / 32767.5f) - 1.f;
+}
 
 const WebUChar* const GamepadSubTypeName(BYTE sub_type) {
   switch (sub_type) {
@@ -162,10 +164,10 @@ void GamepadPlatformDataFetcherWin::GetGamepadData(WebGamepads* pads,
 #undef ADD
       pad.axesLength = 0;
       // XInput are +up/+right, -down/-left, we want -up/-left.
-      pad.axes[pad.axesLength++] = state.Gamepad.sThumbLX / kMaxWinAxisValue;
-      pad.axes[pad.axesLength++] = -state.Gamepad.sThumbLY / kMaxWinAxisValue;
-      pad.axes[pad.axesLength++] = state.Gamepad.sThumbRX / kMaxWinAxisValue;
-      pad.axes[pad.axesLength++] = -state.Gamepad.sThumbRY / kMaxWinAxisValue;
+      pad.axes[pad.axesLength++] = NormalizeAxis(state.Gamepad.sThumbLX);
+      pad.axes[pad.axesLength++] = -NormalizeAxis(state.Gamepad.sThumbLY);
+      pad.axes[pad.axesLength++] = NormalizeAxis(state.Gamepad.sThumbRX);
+      pad.axes[pad.axesLength++] = -NormalizeAxis(state.Gamepad.sThumbRY);
     } else {
       pad.connected = false;
     }