Multiple DPI Tracking for ScreenWin

ui/gfx/win/rect_util.cc

Index: ui/gfx/win/rect_util.cc
diff --git a/ui/gfx/win/rect_util.cc b/ui/gfx/win/rect_util.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0ff294d5b3e5b24b7fde0af5754e1d41533c0df2
--- /dev/null
+++ b/ui/gfx/win/rect_util.cc
@@ -0,0 +1,240 @@
+// Copyright 2016 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/gfx/win/rect_util.h"
+
+#include <algorithm>
+
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/safe_integer_conversions.h"
+#include "ui/gfx/geometry/size.h"
+#include "ui/gfx/geometry/vector2d.h"
+#include "ui/gfx/range/range.h"
+
+namespace {
+
+enum class RelativePosition {
+  BOTTOM = 0,
+  LEFT = 1,
+  TOP = 2,
+  RIGHT = 3,
+};
+
+gfx::Rect CoordinateRotateRectangle90(const gfx::Rect& rect) {
+  return gfx::Rect(rect.y(), -rect.x() - rect.width(),
+                   rect.height(), rect.width());
+}
+
+gfx::Rect CoordinateRotateRectangle180(const gfx::Rect& rect) {
+  return gfx::Rect(-rect.x() - rect.width(), -rect.y() -rect.height(),
+                   rect.width(), rect.height());
+}
+
+gfx::Rect CoordinateRotateRectangle270(const gfx::Rect& rect) {
+  return gfx::Rect(-rect.y() - rect.height(), rect.x(),
+                   rect.height(), rect.width());
+}
+
+gfx::Rect CoordinateReflectRectangleYAxis(const gfx::Rect& rect) {
+  return gfx::Rect(-rect.x() - rect.width(), rect.y(),
+                   rect.width(), rect.height());
+}
+
+gfx::Rect CanonicalizeRelativePosition(const gfx::Rect& rect,
+                                       RelativePosition relative_position) {
+  switch (relative_position) {
+    case RelativePosition::LEFT:
+      return CoordinateRotateRectangle90(rect);
+    case RelativePosition::TOP:
+      return CoordinateRotateRectangle180(rect);
+    case RelativePosition::RIGHT:
+      return CoordinateRotateRectangle270(rect);
+  }
+  return rect;
+}
+
+gfx::Rect CanonicalizeTouchingEdge(const gfx::Rect& rect,
+                                   gfx::win::RectEdge edge) {
+  switch (edge) {
+    case gfx::win::RectEdge::LEFT:
+      return CoordinateRotateRectangle90(rect);

[sky, 2016/02/17 17:28:48]

Can you elaborate on why we need the rotation?

[robliao, 2016/02/18 00:34:38]

The rotation allows us to take advantage of the rotational symmetry of
positioning a rectangle along an edge.

This avoids the need to consider cases for positioning on the right edge (need
to move the unscaled rectangle y location), top edge (need to move the unscaled
rectangle x location and position the bottom edge to match the top edge of the
reference rectangle), and left edge (need to move the unscaled y location and
position the right edge at the left edge of the reference rectangle).

All of these positions can be canonicalized to the same one, so the workflow
is...

[Rotational Transform - Canonicalize to desired orientation]
[Perform Scaling Calculations]
[Revert the Rotational Transform if necessary]

+    case gfx::win::RectEdge::TOP:
+      // Helps prefer left and top alignment.
+      return CoordinateReflectRectangleYAxis(
+          CoordinateRotateRectangle180(rect));
+    case gfx::win::RectEdge::RIGHT:
+      // Helps prefer left and top alignment.
+      return CoordinateReflectRectangleYAxis(
+          CoordinateRotateRectangle270(rect));
+  }
+  return rect;
+}
+
+// Inverse of CanonicalizeTouchingEdge.
+gfx::Rect RevertToOriginalEdge(const gfx::Rect& rect, gfx::win::RectEdge edge) {
+  switch (edge) {
+    case gfx::win::RectEdge::LEFT:
+      return CoordinateRotateRectangle270(rect);
+    case gfx::win::RectEdge::TOP:
+      return CoordinateRotateRectangle180(
+          CoordinateReflectRectangleYAxis(rect));
+    case gfx::win::RectEdge::RIGHT:
+      return CoordinateRotateRectangle90(
+          CoordinateReflectRectangleYAxis(rect));
+  }
+  return rect;
+}
+
+bool InRange(int target, int lower_bound, int upper_bound) {
+  return lower_bound <= target && target <= upper_bound;
+}
+
+// Scales |val| within |old_min| and |old_max| to |new_min| and |new_max|.
+int ScaleValue(int new_min, int new_max, int old_min, int old_max, int val) {
+  int old_delta = old_max - old_min;
+  if (old_delta == 0) {
+    DCHECK_EQ(new_min, new_max);
+    return new_min;
+  }
+  float percent =
+      static_cast<float>(val - old_min) / static_cast<float>(old_delta);
+  return new_min + gfx::ToFlooredInt(percent * (float)(new_max - new_min));
+}
+
+RelativePosition RectRelativePosition(const gfx::Rect& ref,
+                                      const gfx::Rect& test) {
+  if (ref.bottom() <= test.y())
+    return RelativePosition::BOTTOM;
+  else if (test.right() <= ref.x())
+    return RelativePosition::LEFT;
+  else if (test.bottom() <= ref.y())
+    return RelativePosition::TOP;
+
+  return RelativePosition::RIGHT;
+}
+
+}  // namespace
+
+namespace gfx {
+namespace win {
+
+RectEdge FindTouchingRectEdge(const gfx::Rect& ref, const gfx::Rect& test) {

[sky, 2016/02/17 04:40:28]

Add description, in particular who the return value is relative to.

[robliao, 2016/02/18 00:34:39]

Done for RectRelativePosition. The header contains this info:
// Returns |ref|'s RectEdge touching |test|.

+  int max_x = std::max(ref.x(), test.x());

[sky, 2016/02/17 17:28:48]

This functions seems more complex than it needs to be. Why not something like:

if (ref.right() == test.x())
  return RIGHT;
if (ref.x() == test.right())
  return LEFT;
if (ref.y() == test.bottom())
  return TOP;
if (ref.bottom() == test.y())
  return BOTTOM;
return NONE;

?
It's entirely possible I have the left/right backwards.As I said, I'm not sure
which rect the direction is relative to.

[robliao, 2016/02/18 00:34:39]

We need to do the intersection test because a rectangle may satisfy some of the
conditions in the suggested code snippet and still not touch. For example,
consider two rectangles REF and TEST:

x-values
0123456789
+---+
|REF|
+---+

    +----+
    |TEST|
    +----+

REF.right() == 4 == TEST.x()
The code snippet above would say that REF's right edge touches TEST when it
should return NONE.

The edge orientation is documented in the header file:
// Returns |ref|'s RectEdge touching |test|.

+  int max_y = std::max(ref.y(), test.y());
+  int min_right = std::min(ref.right(), test.right());
+  int min_bottom = std::min(ref.bottom(), test.bottom());
+  if (max_x == min_right && max_y == min_bottom) {
+    // Corner touching.
+    if (ref.bottom() == max_y)
+      return RectEdge::BOTTOM;
+    else if (ref.x() == max_x)
+      return RectEdge::LEFT;
+
+    return RectEdge::TOP;
+  } else if (max_x == min_right) {

[sky, 2016/02/17 04:40:28]

nit: no else after return.

[robliao, 2016/02/18 00:34:39]

Done.

+    // Vertical edge touching.
+    return ref.x() == max_x ? RectEdge::LEFT : RectEdge::RIGHT;
+  } else if (max_y == min_bottom) {
+    // Horizontal edge touching.
+    return ref.y() == max_y ? RectEdge::TOP : RectEdge::BOTTOM;
+  }
+  return RectEdge::NONE;
+}
+
+// Writing code that specifically deals with scaling each rect is tedious and
+// error prone. Instead, this function transforms the positions of the
+// two rects so that |ref_scaled_rect| is always on top of |ref_original_rect|,
+// calculates the scaled and positioned target rect, and then reverses the
+// transforms. As a result, the position logic can be written in terms of the
+// bottom of the |ref_original_rect| instead of the bottom, left, top, and
+// right.
+gfx::Rect ScaleAndPositionRect(gfx::Rect ref_scaled_rect,
+                               gfx::Rect ref_original_rect,
+                               gfx::Rect target_rect,
+                               float target_scale_factor) {
+  RectEdge orig_edge = FindTouchingRectEdge(ref_original_rect, target_rect);
+
+  // Scale size only since the scaled origin location will be determined below.
+  gfx::Rect scaled_rect = gfx::ScaleToEnclosingRect(target_rect,
+                                                    1.0f / target_scale_factor);
+  scaled_rect.set_origin(gfx::Point(0, 0));
+
+  if (orig_edge == RectEdge::NONE) {
+    // Currently, we expect all rectangles to touch each other.
+    NOTREACHED();

[sky, 2016/02/17 17:28:48]

If that's the case, then 164 should be a DCHECK.

[robliao, 2016/02/18 00:34:39]

Done.

+    scaled_rect.set_origin(target_rect.origin());
+  }
+
+  // Transform rectangles so we can simply deal with bottom edge sharing.
+  ref_scaled_rect = CanonicalizeTouchingEdge(ref_scaled_rect, orig_edge);
+  ref_original_rect = CanonicalizeTouchingEdge(ref_original_rect, orig_edge);
+  target_rect = CanonicalizeTouchingEdge(target_rect, orig_edge);
+  scaled_rect = CanonicalizeTouchingEdge(scaled_rect, orig_edge);
+
+  // Position the rect.
+  scaled_rect.set_y(ref_scaled_rect.bottom());
+  int x;
+  if (target_rect.right() == ref_original_rect.right()) {
+    // Maintain right alignment. If the rectangle was left-aligned, the next
+    // case will catch that.
+    x = ref_scaled_rect.right() - scaled_rect.width();
+  } else if (InRange(target_rect.x(),
+                     ref_original_rect.x(),
+                     ref_original_rect.right())) {
+    // Position using the left point relative to the reference rect.
+    x = ScaleValue(ref_scaled_rect.x(), ref_scaled_rect.right(),
+                   ref_original_rect.x(), ref_original_rect.right(),
+                   target_rect.x());
+  } else if (InRange(target_rect.right(),
+                     ref_original_rect.x(),
+                     ref_original_rect.right())) {
+    // Position using the right point relative to the reference rect.
+    x = ScaleValue(ref_scaled_rect.x(), ref_scaled_rect.right(),
+                   ref_original_rect.x(), ref_original_rect.right(),
+                   target_rect.right()) - scaled_rect.width();
+  } else if (InRange(ref_scaled_rect.x(),
+                     target_rect.x(),
+                     target_rect.right())) {
+    // Position relative to the left point of the reference rect.
+    int offset = ScaleValue(0, scaled_rect.width(),
+                            0, target_rect.width(),
+                            ref_original_rect.x() - target_rect.x());
+    x = ref_scaled_rect.x() - offset;
+  } else {
+    // Position relative to the right point of the reference rect.
+    int offset = ScaleValue(0, scaled_rect.width(),
+                            0, target_rect.width(),
+                            ref_original_rect.right() - target_rect.x());
+    x = ref_scaled_rect.x() - offset - scaled_rect.width();
+  }
+  scaled_rect.set_x(x);
+  DCHECK(
+      FindTouchingRectEdge(ref_scaled_rect, scaled_rect) == RectEdge::BOTTOM);
+
+  // Reverse the transformation.
+  return RevertToOriginalEdge(scaled_rect, orig_edge);
+}
+
+// This function takes the same approach as ScaleAndPositionRect, transforming
+// the two input rects so that the relative positions are always the same.
+int64_t SquaredDistanceBetweenRects(gfx::Rect ref, gfx::Rect rect) {
+  if (ref.Intersects(rect))
+    return 0;
+
+  RelativePosition relative_position = RectRelativePosition(ref, rect);
+  ref = CanonicalizeRelativePosition(ref, relative_position);
+  rect = CanonicalizeRelativePosition(rect, relative_position);
+  // Now that the ref is on top, we can concentrate ref bottom
+  // and rect top calculations.
+  if (rect.right() < ref.x())
+    return (rect.top_right() - ref.bottom_left()).LengthSquared();
+  else if (ref.right() < rect.x())
+    return (rect.origin() - ref.bottom_right()).LengthSquared();
+
+  int distance = rect.y() - ref.bottom();
+  return distance * distance;
+}
+
+}  // namespace win
+}  // namespace gfx