ozone: evdev: Fix tilt calculation for tablets

ui/events/ozone/evdev/tablet_event_converter_evdev.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/ozone/evdev/tablet_event_converter_evdev.h"
 
 #include <errno.h>
 #include <linux/input.h>
 
 #include "base/message_loop/message_loop.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/events/event.h"
 #include "ui/events/ozone/evdev/device_event_dispatcher_evdev.h"
 
 namespace ui {
 
+namespace {
+
+// Convert tilt from [min, min + num_values) to [-90deg, +90deg)
+float ScaleTilt(int value, int min_value, int num_values) {
+  return 180.f * (value - min_value) / num_values - 90.f;
+}
+
+}  // namespace
+
 TabletEventConverterEvdev::TabletEventConverterEvdev(
     int fd,
     base::FilePath path,
     int id,
     CursorDelegateEvdev* cursor,
     const EventDeviceInfo& info,
     DeviceEventDispatcherEvdev* dispatcher)
     : EventConverterEvdev(fd,
                           path,
                           id,
                           info.device_type(),
                           info.name(),
                           info.vendor_id(),
                           info.product_id()),
       cursor_(cursor),
       dispatcher_(dispatcher) {
   x_abs_min_ = info.GetAbsMinimum(ABS_X);
   x_abs_range_ = info.GetAbsMaximum(ABS_X) - x_abs_min_ + 1;
   y_abs_min_ = info.GetAbsMinimum(ABS_Y);
   y_abs_range_ = info.GetAbsMaximum(ABS_Y) - y_abs_min_ + 1;
-
-  tilt_x_max_ = info.GetAbsMaximum(ABS_TILT_X);
-  tilt_y_max_ = info.GetAbsMaximum(ABS_TILT_Y);
+  tilt_x_min_ = info.GetAbsMinimum(ABS_TILT_X);
+  tilt_y_min_ = info.GetAbsMinimum(ABS_TILT_Y);
+  tilt_x_range_ = info.GetAbsMaximum(ABS_TILT_X) - tilt_x_min_ + 1;

[mustaq, 2015/11/19 15:26:35]

Have a quick question, didn't see it until CQing, sorry.

Does GetAbsMaximum() return the max possible raw "value" from device, or one off
from that? Because, intuitively, range = max-min, and thus the angle is +90 when
the "value" == max:
  180 * (max-min)/(max-min) - 90

+  tilt_y_range_ = info.GetAbsMaximum(ABS_TILT_Y) - tilt_y_min_ + 1;
   pressure_max_ = info.GetAbsMaximum(ABS_PRESSURE);
 }
 
 TabletEventConverterEvdev::~TabletEventConverterEvdev() {
 }
 
 void TabletEventConverterEvdev::OnFileCanReadWithoutBlocking(int fd) {
   TRACE_EVENT1("evdev",
                "TabletEventConverterEvdev::OnFileCanReadWithoutBlocking", "fd",
                fd);
@@ skipping 59 matching lines @@
   switch (input.code) {
     case ABS_X:
       x_abs_location_ = input.value;
       abs_value_dirty_ = true;
       break;
     case ABS_Y:
       y_abs_location_ = input.value;
       abs_value_dirty_ = true;
       break;
     case ABS_TILT_X:
-      tilt_x_ = (90.0f * input.value) / tilt_x_max_;
+      tilt_x_ = ScaleTilt(input.value, tilt_x_min_, tilt_x_range_);
       abs_value_dirty_ = true;
       break;
     case ABS_TILT_Y:
-      tilt_y_ = (90.0f * input.value) / tilt_y_max_;
+      tilt_y_ = ScaleTilt(input.value, tilt_y_min_, tilt_y_range_);
       abs_value_dirty_ = true;
       break;
     case ABS_PRESSURE:
       pressure_ = (float)input.value / pressure_max_;
       abs_value_dirty_ = true;
       break;
   }
 }
 
 void TabletEventConverterEvdev::UpdateCursor() {
@@ skipping 60 matching lines @@
       input_device_.id, cursor_->GetLocation(),
       PointerDetails(EventPointerType::POINTER_TYPE_PEN,
                      /* radius_x */ 0.0f, /* radius_y */ 0.0f, pressure_,
                      tilt_x_, tilt_y_),
       TimeDeltaFromInputEvent(input)));
 
   abs_value_dirty_ = false;
 }
 
 }  // namespace ui