ozone: Add low pressure filter for touchscreen

To prevent poor quality touches on hana, add a filter for low pressure
touches, such as those generated by a pencil.  Finger presses are above
the chosen threshold and aren't affected.  If a contact ever exceeds the
presure threshold, all remaining events for that contact are sent.

CQ-DEPEND=CL:1093584
BUG=b:69232663
TEST=manual testing on hana with pressure filter enabled

Change-Id: Ic2d56eb656e318ee46744ef37f6055d8573a2261
Reviewed-on: https://chromium-review.googlesource.com/1096126Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Commit-Queue: Sean O'Brien <seobrien@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569415}

chrome/browser/chromeos/login/chrome_restart_request.cc

@@ -134,6 +134,7 @@ void DeriveCommandLine(const GURL& start_url,
     ::switches::kGpuRasterizationMSAASampleCount,
     ::switches::kGpuStartupDialog,
     ::switches::kGpuSandboxStartEarly,
+    ::switches::kLowPressureTouchFiltering,
     ::switches::kNumRasterThreads,
     ::switches::kPpapiFlashArgs,
     ::switches::kPpapiFlashPath,

ui/events/event_switches.cc

@@ -39,6 +39,10 @@ const char kTouchCalibration[] = "touch-calibration";
 
 // Tells Chrome to do edge touch filtering. Useful for convertible tablet.
 const char kEdgeTouchFiltering[] = "edge-touch-filtering";
+
+// Tells Chrome to do filter out low pressure touches, as from a pencil. Should
+// only be used if the driver level filtering is insufficient.
+const char kLowPressureTouchFiltering[] = "low-pressure-touch-filtering";
 #endif
 
 }  // namespace switches

ui/events/event_switches.h

@@ -23,6 +23,7 @@ EVENTS_BASE_EXPORT extern const char kPenDevices[];
 EVENTS_BASE_EXPORT extern const char kExtraTouchNoiseFiltering[];
 EVENTS_BASE_EXPORT extern const char kTouchCalibration[];
 EVENTS_BASE_EXPORT extern const char kEdgeTouchFiltering[];
+EVENTS_BASE_EXPORT extern const char kLowPressureTouchFiltering[];
 #endif
 
 }  // namespace switches

ui/events/ozone/BUILD.gn

@@ -117,6 +117,8 @@ if (use_ozone) {
       "evdev/touch_filter/far_apart_taps_touch_noise_filter.h",
       "evdev/touch_filter/horizontally_aligned_touch_noise_filter.cc",
       "evdev/touch_filter/horizontally_aligned_touch_noise_filter.h",
+      "evdev/touch_filter/low_pressure_filter.cc",
+      "evdev/touch_filter/low_pressure_filter.h",
       "evdev/touch_filter/single_position_touch_noise_filter.cc",
       "evdev/touch_filter/single_position_touch_noise_filter.h",
       "evdev/touch_filter/touch_filter.h",

ui/events/ozone/evdev/touch_filter/false_touch_finder.cc

@@ -12,6 +12,7 @@
 #include "ui/events/ozone/evdev/touch_filter/edge_touch_filter.h"
 #include "ui/events/ozone/evdev/touch_filter/far_apart_taps_touch_noise_filter.h"
 #include "ui/events/ozone/evdev/touch_filter/horizontally_aligned_touch_noise_filter.h"
+#include "ui/events/ozone/evdev/touch_filter/low_pressure_filter.h"
 #include "ui/events/ozone/evdev/touch_filter/single_position_touch_noise_filter.h"
 #include "ui/events/ozone/evdev/touch_filter/touch_filter.h"
 
@@ -25,9 +26,13 @@ std::unique_ptr<FalseTouchFinder> FalseTouchFinder::Create(
       switches::kExtraTouchNoiseFiltering);
   bool edge_filtering = base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEdgeTouchFiltering);
-  if (noise_filtering || edge_filtering) {
-    return base::WrapUnique(new FalseTouchFinder(
-        noise_filtering, edge_filtering, touchscreen_size));
+  bool low_pressure_filtering =
+      base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kLowPressureTouchFiltering);
+  if (noise_filtering || edge_filtering || low_pressure_filtering) {
+    return base::WrapUnique(
+        new FalseTouchFinder(noise_filtering, edge_filtering,
+                             low_pressure_filtering, touchscreen_size));
   }
   return nullptr;
 }
@@ -62,6 +67,7 @@ bool FalseTouchFinder::SlotShouldDelay(size_t slot) const {
 
 FalseTouchFinder::FalseTouchFinder(bool noise_filtering,
                                    bool edge_filtering,
+                                   bool low_pressure_filtering,
                                    gfx::Size touchscreen_size)
     : last_noise_time_(ui::EventTimeForNow()) {
   if (noise_filtering) {
@@ -75,6 +81,9 @@ FalseTouchFinder::FalseTouchFinder(bool noise_filtering,
     delay_filters_.push_back(
         std::make_unique<EdgeTouchFilter>(touchscreen_size));
   }
+  if (low_pressure_filtering) {
+    delay_filters_.push_back(std::make_unique<LowPressureFilter>());
+  }
 }
 
 void FalseTouchFinder::RecordUMA(bool had_noise, base::TimeTicks time) {

ui/events/ozone/evdev/touch_filter/false_touch_finder.h

@@ -45,6 +45,7 @@ class EVENTS_OZONE_EVDEV_EXPORT FalseTouchFinder {
  private:
   FalseTouchFinder(bool touch_noise_filtering,
                    bool edge_filtering,
+                   bool low_pressure_filtering,
                    gfx::Size touchscreen_size);
 
   // Records how frequently noisy touches occur to UMA.

ui/events/ozone/evdev/touch_filter/low_pressure_filter.cc

+// Copyright 2017 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/touch_filter/low_pressure_filter.h"
+
+#include <stddef.h>
+
+#include <cmath>
+
+#include "base/macros.h"
+
+namespace ui {
+
+namespace {
+
+const float kMinPressure = 0.19;
+
+}  // namespace
+
+LowPressureFilter::LowPressureFilter() {}
+LowPressureFilter::~LowPressureFilter() {}
+
+void LowPressureFilter::Filter(
+    const std::vector<InProgressTouchEvdev>& touches,
+    base::TimeTicks time,
+    std::bitset<kNumTouchEvdevSlots>* slots_should_delay) {
+  for (const InProgressTouchEvdev& touch : touches) {
+    size_t slot = touch.slot;
+
+    if (!touch.touching && !touch.was_touching)
+      continue;  // Only look at slots with active touches.
+
+    if (!touch.was_touching)
+      slots_filtered_.set(slot, true);  // Start tracking a new touch.
+
+    if (touch.pressure >= kMinPressure)
+      slots_filtered_.set(slot, false);  // Release touches above threshold.
+  }
+
+  (*slots_should_delay) |= slots_filtered_;
+}
+
+}  // namespace ui

ui/events/ozone/evdev/touch_filter/low_pressure_filter.h

+// Copyright 2017 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.
+
+#ifndef UI_EVENTS_OZONE_EVDEV_TOUCH_FILTER_LOW_PRESSURE_FILTER_H_
+#define UI_EVENTS_OZONE_EVDEV_TOUCH_FILTER_LOW_PRESSURE_FILTER_H_
+
+#include "base/macros.h"
+#include "base/time/time.h"
+#include "ui/events/event_utils.h"
+#include "ui/events/ozone/evdev/touch_filter/touch_filter.h"
+
+namespace ui {
+
+class LowPressureFilter : public TouchFilter {
+ public:
+  LowPressureFilter();
+  ~LowPressureFilter() override;
+
+  // TouchFilter:
+  void Filter(const std::vector<InProgressTouchEvdev>& touches,
+              base::TimeTicks time,
+              std::bitset<kNumTouchEvdevSlots>* slots_should_delay) override;
+
+ private:
+  std::bitset<kNumTouchEvdevSlots> slots_filtered_;
+
+  DISALLOW_COPY_AND_ASSIGN(LowPressureFilter);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_OZONE_EVDEV_TOUCH_FILTER_LOW_PRESSURE_FILTER_H_