Introduce AccessibilityFocusRing.

chrome/browser/chromeos/ui/accessibility_focus_ring_layer.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 "chrome/browser/chromeos/ui/accessibility_focus_ring_layer.h"
+
+#include "ash/shell.h"
+#include "base/bind.h"
+#include "ui/aura/window.h"
+#include "ui/compositor/layer.h"
+#include "ui/gfx/canvas.h"
+
+namespace chromeos {
+
+namespace {
+
+// The number of pixels in the color gradient that fades to transparent.
+const int kGradientWidth = 10;
+
+// The color of the focus ring. In the future this might be a parameter.
+const int kFocusRingColorRed = 247;
+const int kFocusRingColorGreen = 152;
+const int kFocusRingColorBlue = 58;
+
+int sign(int x) {
+  return ((x > 0) ? 1 : (x == 0) ? 0 : -1);
+}
+
+SkPath MakePath(const AccessibilityFocusRing& input_ring,
+                int outset,
+                const gfx::Vector2d& offset) {
+  AccessibilityFocusRing ring = input_ring;
+
+  for (int i = 0; i < 36; i++) {
+    gfx::Point p = input_ring.points[i];
+    gfx::Point prev;
+    gfx::Point next;
+
+    int prev_index = i;
+    do {
+      prev_index = (prev_index + 35) % 36;
+      prev = input_ring.points[prev_index];
+    } while (prev.x() == p.x() && prev.y() == p.y());
+
+    int next_index = i;
+    do {
+      next_index = (next_index + 1) % 36;
+      next = input_ring.points[next_index];
+    } while (next.x() == p.x() && next.y() == p.y());
+
+    gfx::Point delta0 = gfx::Point(sign(p.x() - prev.x()),
+                                   sign(p.y() - prev.y()));
+    gfx::Point delta1 = gfx::Point(sign(next.x() - p.x()),
+                                   sign(next.y() - p.y()));
+
+    if (delta0.x() == delta1.x() && delta0.y() == delta1.y()) {
+      ring.points[i] = gfx::Point(
+          input_ring.points[i].x() + outset * delta0.y(),
+          input_ring.points[i].y() - outset * delta0.x());
+    } else {
+      ring.points[i] = gfx::Point(
+          input_ring.points[i].x() + ((i + 13) % 36 >= 18 ? outset : -outset),
+          input_ring.points[i].y() + ((i + 4) % 36 >= 18 ? outset : -outset));
+    }
+  }
+
+  SkPath path;
+  gfx::Point p0 = ring.points[0] - offset;
+  path.moveTo(SkIntToScalar(p0.x()), SkIntToScalar(p0.y()));
+  for (int i = 0; i < 12; i++) {
+    int index0 = ((3 * i) + 1) % 36;
+    int index1 = ((3 * i) + 2) % 36;
+    int index2 = ((3 * i) + 3) % 36;
+    gfx::Point p0 = ring.points[index0] - offset;
+    gfx::Point p1 = ring.points[index1] - offset;
+    gfx::Point p2 = ring.points[index2] - offset;
+    path.lineTo(SkIntToScalar(p0.x()), SkIntToScalar(p0.y()));
+    path.quadTo(SkIntToScalar(p1.x()), SkIntToScalar(p1.y()),
+                SkIntToScalar(p2.x()), SkIntToScalar(p2.y()));
+  }
+
+  return path;
+}
+
+}  // namespace
+
+AccessibilityFocusRingLayer::AccessibilityFocusRingLayer(
+    FocusRingLayerDelegate* delegate)
+    : FocusRingLayer(delegate) {
+}
+
+AccessibilityFocusRingLayer::~AccessibilityFocusRingLayer() {}
+
+void AccessibilityFocusRingLayer::Set(const AccessibilityFocusRing& ring) {
+  ring_ = ring;
+
+  gfx::Rect bounds = ring.GetBounds();
+  int inset = kGradientWidth;
+  bounds.Inset(-inset, -inset, -inset, -inset);
+
+  if (!layer_) {
+    aura::Window* root_window = ash::Shell::GetPrimaryRootWindow();

[xiyuan, 2014/09/11 03:57:45]

Primary root window might not always be right. We probably should figure out
which root window contains |ring_|.

It seems we could do something like this:
gfx::Display display =
    gfx::Screen::GetNativeScreen()->GetDisplayMatching(bounds);
aura::Window* root_window = ash::Shell::GetInstance()->display_controller()
    ->GetRootWindowForDisplayId(display.id);

[dmazzoni, 2014/09/11 21:44:39]

Great! I knew this needed to be done but wasn't sure how, thanks for making it
easy for me.

I took this opportunity to move the next block of code into focus_ring_layer and
share it, since they're now identical.

+    ui::Layer* root_layer = root_window->layer();
+    layer_.reset(new ui::Layer(ui::LAYER_TEXTURED));
+    layer_->set_name("AccessibilityFocusRing");
+    layer_->set_delegate(this);
+    layer_->SetFillsBoundsOpaquely(false);
+    root_layer->Add(layer_.get());
+  }
+
+  // Keep moving it to the top in case new layers have been added
+  // since we created this layer.
+  layer_->parent()->StackAtTop(layer_.get());
+
+  // Update the layer bounds.
+  layer_->SetBounds(bounds);
+}
+
+void AccessibilityFocusRingLayer::OnPaintLayer(gfx::Canvas* canvas) {
+  gfx::Vector2d offset = layer_->bounds().OffsetFromOrigin();
+
+  SkPaint paint;
+  paint.setFlags(SkPaint::kAntiAlias_Flag);
+  paint.setStyle(SkPaint::kStroke_Style);
+  paint.setStrokeWidth(2);
+
+  SkPath path;
+  for (int i = 0; i < kGradientWidth; i++) {
+    paint.setColor(
+        SkColorSetARGBMacro(
+            255 - (255 * i / kGradientWidth),
+            kFocusRingColorRed, kFocusRingColorGreen, kFocusRingColorBlue));
+    path = MakePath(ring_, i, offset);
+    canvas->DrawPath(path, paint);
+  }
+}
+
+}  // namespace chromeos