Port Chromium OS touch noise filtering to Chromium

ui/events/ozone/evdev/touch_noise/far_apart_taps_touch_noise_filter.cc

+// Copyright 2015 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_noise/far_apart_taps_touch_noise_filter.h"
+
+#include <cmath>
+
+#include "base/logging.h"
+#include "base/strings/stringprintf.h"
+
+namespace ui {
+
+namespace {
+
+// Minimum squared distance between taps to be considered far apart.
+const int kMinDistance2 = 1500 * 1500;
+
+// Max time between taps considered.
+const int kMaxTapDeltaMs = 30;
+
+// Maximum squared movement of a touch to still be considered a tap.
+const int kMaxTapMovement2 = 20 * 20;
+
+// Returns the squared distance between (|x1|, |y1|) and (|x2|, |y2|).
+int Distance2(int x1, int y1, int x2, int y2) {
+  int offset_x = x2 - x1;
+  int offset_y = y2 - y1;
+  return offset_x * offset_x + offset_y * offset_y;
+}
+
+}  // namespace
+
+void FarApartTapsTouchNoiseFilter::Filter(
+    const std::vector<InProgressTouchEvdev>& touches,
+    base::TimeDelta time,
+    std::bitset<kNumTouchEvdevSlots>* slots_with_noise) {
+  // Remove old taps.
+  base::TimeDelta tap_cutoff =
+      time - base::TimeDelta::FromMilliseconds(kMaxTapDeltaMs);
+  for (size_t i = 0; i < arraysize(tracked_taps_); ++i) {
+    if (tracked_taps_[i].start < tap_cutoff)
+      tracked_taps_[i].Invalidate();
+  }
+
+  for (const InProgressTouchEvdev& touch : touches) {
+    // Only look at slots with active touches.
+    if (!touch.touching && !touch.was_touching)
+      continue;
+
+    size_t slot = touch.slot;
+    if (!touch.was_touching) {
+      // Track new finger info.
+      tracked_taps_[slot] = Tap(time, touch.x, touch.y);
+    } else if (tracked_taps_[slot].is_valid()) {
+      // Check if this finger has moved too far to be considered a tap.
+      if (kMaxTapMovement2 < Distance2(touch.x, touch.y, tracked_taps_[slot].x,
+                                       tracked_taps_[slot].y)) {
+        tracked_taps_[slot].Invalidate();
+      }
+    }
+
+    if (tracked_taps_[slot].is_valid()) {
+      // Check distance from other tracked taps.
+      int min_distance2 = -1;
+      for (size_t i = 0; i < arraysize(tracked_taps_); ++i) {
+        if (i == slot || !tracked_taps_[i].is_valid())
+          continue;
+
+        int dist2 =
+            Distance2(tracked_taps_[i].x, tracked_taps_[i].y, touch.x, touch.y);
+        if (min_distance2 < 0 || dist2 < min_distance2)
+          min_distance2 = dist2;
+      }
+
+      if (min_distance2 > kMinDistance2) {
+        // The other finger should see this one on its next frame and also
+        // get canceled.
+        VLOG(2) << base::StringPrintf(
+            "Cancel tracking id %d %.0fpx from other current taps.",
+            touch.tracking_id, sqrt(min_distance2));
+        slots_with_noise->set(slot);
+      }
+    }
+
+    if (!touch.touching)
+      tracked_taps_[slot].Invalidate();
+  }
+}
+
+}  // namespace ui