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// 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.
#ifndef CHROME_BROWSER_CHROMEOS_UI_ACCESSIBILITY_FOCUS_RING_H_
#define CHROME_BROWSER_CHROMEOS_UI_ACCESSIBILITY_FOCUS_RING_H_
#include "ui/gfx/geometry/point.h"
#include "ui/gfx/geometry/rect.h"
namespace chromeos {
// An AccessibilityFocusRing is a special type of shape designed to
// outline the focused object on the screen for users with visual
// impairments. It's specifically designed to outline text ranges that
// span multiple lines (we'll call this a "paragraph" shape from here on,
// but it works for any text range), so it can outline a shape defined by a
// few words from the first line, the complete contents of more lines,
// followed by a few words from the last line. See the figure below.
// When highlighting any other object, it outlines a rectangular shape.
//
// The outline is outset from the object it's highlighting by a few pixels;
// this margin distance also determines its border radius for rounded
// corners.
//
// An AccessibilityFocusRing can be initialized with either a rectangle
// defining the bounds of an object, or a paragraph-shape with three
// rectangles defining a top line, a body, and a bottom line, which are
// assumed to be adjacent to one another.
//
// Initializing an AccessibilityFocusRing computes the following 36 points
// that completely define the shape's outline. This shape can be traced
// using Skia or any other drawing utility just by drawing alternating
// straight lines and quadratic curves (e.g. a line from 0 to 1, a curve
// from 1 to 3 with 2 as a control point, then a line from 3 to 4, and so on.
//
// The same path should be used even if the focus ring was initialized with
// a rectangle and not a paragraph shape - this makes it possible to
// smoothly animate between one object and the next simply by interpolating
// points.
//
// Noncontiguous shapes should be handled by drawing multiple focus rings.
//
// The 36 points are defined as follows:
//
// 2 3------------------------------4 5
// / |
// 1 6
// | First line of paragraph |
// 0 7
// / |
// 32 33-34 35 8 9---------------10 11
// / |
// 31 Middle line of paragraph.......................... 12
// | |
// | |
// | Middle line of paragraph.......................... |
// | |
// | |
// 30 Middle line of paragraph.......................... 13
// | |
// 29 28---------27 26 17 16---------15 14
// | |
// 25 18
// | Last line of paragraph |
// 24 19
// | |
// 23 22-----------------------21 20
struct AccessibilityFocusRing {
// Construct an AccessibilityFocusRing that outlines a rectangular object.
static AccessibilityFocusRing CreateWithRect(
const gfx::Rect& bounds, int margin);
// Returns a ring where 0.0 returns r1, 1.0 returns r2, and any number
// in-between interpolates linearly between them.
static AccessibilityFocusRing Interpolate(
const AccessibilityFocusRing& r1,
const AccessibilityFocusRing& r2,
double fraction);
// Construct an AccessibilityFocusRing that outlines a paragraph-shaped
// object.
static AccessibilityFocusRing CreateWithParagraphShape(
const gfx::Rect& top_line,
const gfx::Rect& body,
const gfx::Rect& bottom_line,
int margin);
gfx::Rect GetBounds() const;
gfx::Point points[36];
};
} // namespace chromeos
#endif // CHROME_BROWSER_CHROMEOS_UI_ACCESSIBILITY_FOCUS_RING_H_
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