Implement disambiguation popup

content/renderer/disambiguation_popup_helper.cc

+// Copyright (c) 2012 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 "content/renderer/disambiguation_popup_helper.h"
+
+#include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebRect.h"
+
+using WebKit::WebRect;
+using WebKit::WebVector;
+
+namespace {
+
+// The amount of padding to add to the disambiguation popup to show
+// content around the possible elements, adding some context.
+const int kDisambiguationPopupPadding = 8;
+
+// Constants used for fitting the disambiguation popup inside the bounds of
+// the view. Note that there are mirror constants in PopupZoomer.java.
+const int kDisambiguationPopupBoundsMargin = 25;
+
+// The smallest allowable touch target used for disambiguation popup.
+// This value is used to determine the minimum amount we need to scale to
+// make all targets touchable.
+const int kDisambiguationPopupMinimumTouchSize = 40;
+const float kDisambiguationPopupMaxScale = 5.0;
+const float kDisambiguationPopupMinScale = 2.0;
+
+// Compute the scaling factor to ensure the smallest touch candidate reaches
+// a certain clickable size after zooming
+float FindOptimalScaleFactor(const WebVector<WebRect>& target_rects) {
+  using std::min;
+  using std::max;
+  if (!target_rects.size()) // shall never reach
+    return kDisambiguationPopupMinScale;
+  int smallest_target = min(target_rects[0].width, target_rects[0].height);
+  for (size_t i = 1; i < target_rects.size(); i++) {
+    smallest_target = min(smallest_target, target_rects[i].width);
+    smallest_target = min(smallest_target, target_rects[i].height);
+  }
+  smallest_target = max(smallest_target, 1);
+  return min(kDisambiguationPopupMaxScale, max(kDisambiguationPopupMinScale,
+      static_cast<float>(kDisambiguationPopupMinimumTouchSize)
+          / smallest_target));
+}
+
+void TrimEdges(int *e1, int *e2, int max_combined) {
+  if (*e1 + *e2 <= max_combined)
+    return;
+
+  if (std::min(*e1, *e2) * 2 >= max_combined)
+    *e1 = *e2 = max_combined / 2;
+  else if (*e1 > *e2)
+    *e1 = max_combined - *e2;
+  else
+    *e2 = max_combined - *e1;
+}
+
+// Ensure the disambiguation popup fits inside the screen,
+// clip the edges farthest to the touch point if needed.
+gfx::Rect CropZoomArea(const gfx::Rect& zoom_rect,
+                       const gfx::Size& viewport_size,
+                       const gfx::Point& touch_point,
+                       float scale) {
+    gfx::Size max_size = viewport_size;
+    max_size.Enlarge(-2 * kDisambiguationPopupBoundsMargin,
+                     -2 * kDisambiguationPopupBoundsMargin);
+    max_size = max_size.Scale(1.0 / scale);
+
+    int left = touch_point.x() - zoom_rect.x();
+    int right = zoom_rect.right() - touch_point.x();
+    int top = touch_point.y() - zoom_rect.y();
+    int bottom = zoom_rect.bottom() - touch_point.y();
+    TrimEdges(&left, &right, max_size.width());
+    TrimEdges(&top, &bottom, max_size.height());
+
+    return gfx::Rect(touch_point.x() - left,
+                     touch_point.y() - top,
+                     left + right,
+                     top + bottom);
+}
+
+} // unnamed namespace
+
+float DisambiguationPopupHelper::ComputeZoomAreaAndScaleFactor(

[darin (slow to review), 2012/10/08 21:03:46]

There's enough code in here that I think you could write some good unit tests.

[trchen, 2012/10/11 23:54:05]

Added 3 simple test cases. However all it does is to make sure the output values
have basic sanity, as the behavior is pretty much implementation defined.

+    const gfx::Rect& tap_rect,
+    const WebVector<WebRect>& target_rects,
+    const gfx::Size& viewport_size,
+    gfx::Rect* zoom_rect) {
+  *zoom_rect = tap_rect;
+  for (size_t i = 0; i < target_rects.size(); i++)
+    *zoom_rect = zoom_rect->Union(gfx::Rect(target_rects[i]));
+  zoom_rect->Inset(-kDisambiguationPopupPadding, -kDisambiguationPopupPadding);
+  *zoom_rect = zoom_rect->Intersect(gfx::Rect(viewport_size));
+
+  float scale = FindOptimalScaleFactor(target_rects);
+  *zoom_rect = CropZoomArea(
+      *zoom_rect, viewport_size, tap_rect.CenterPoint(), scale);
+
+  return scale;
+}
+