src/chrome/browser/chromeos/ui/accessibility_focus_ring.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CHROME_BROWSER_CHROMEOS_UI_ACCESSIBILITY_FOCUS_RING_H_
   6 #define CHROME_BROWSER_CHROMEOS_UI_ACCESSIBILITY_FOCUS_RING_H_
   7
   8 #include "ui/gfx/point.h"
   9 #include "ui/gfx/rect.h"
  10
  11 namespace chromeos {
  12
  13 // An AccessibilityFocusRing is a special type of shape designed to
  14 // outline the focused object on the screen for users with visual
  15 // impairments. It's specifically designed to outline text ranges that
  16 // span multiple lines (we'll call this a "paragraph" shape from here on,
  17 // but it works for any text range), so it can outline a shape defined by a
  18 // few words from the first line, the complete contents of more lines,
  19 // followed by a few words from the last line. See the figure below.
  20 // When highlighting any other object, it outlines a rectangular shape.
  21 //
  22 // The outline is outset from the object it's highlighting by a few pixels;
  23 // this margin distance also determines its border radius for rounded
  24 // corners.
  25 //
  26 // An AccessibilityFocusRing can be initialized with either a rectangle
  27 // defining the bounds of an object, or a paragraph-shape with three
  28 // rectangles defining a top line, a body, and a bottom line, which are
  29 // assumed to be adjacent to one another.
  30 //
  31 // Initializing an AccessibilityFocusRing computes the following 36 points
  32 // that completely define the shape's outline. This shape can be traced
  33 // using Skia or any other drawing utility just by drawing alternating
  34 // straight lines and quadratic curves (e.g. a line from 0 to 1, a curve
  35 // from 1 to 3 with 2 as a control point, then a line from 3 to 4, and so on.
  36 //
  37 // The same path should be used even if the focus ring was initialized with
  38 // a rectangle and not a paragraph shape - this makes it possible to
  39 // smoothly animate between one object and the next simply by interpolating
  40 // points.
  41 //
  42 // Noncontiguous shapes should be handled by drawing multiple focus rings.
  43 //
  44 // The 36 points are defined as follows:
  45 //
  46 //          2 3------------------------------4 5
  47 //           /                                |
  48 //          1                                  6
  49 //          |      First line of paragraph     |
  50 //          0                                  7
  51 //         /                                    |
  52 // 32 33-34 35                                 8 9---------------10 11
  53 //   /                                                             |
  54 // 31      Middle line of paragraph..........................       12
  55 // |                                                                |
  56 // |                                                                |
  57 // |       Middle line of paragraph..........................       |
  58 // |                                                                |
  59 // |                                                                |
  60 // 30      Middle line of paragraph..........................       13
  61 //   |                                                             |
  62 // 29 28---------27 26                             17 16---------15 14
  63 //                 |                                 |
  64 //                  25                             18
  65 //                  |    Last line of paragraph    |
  66 //                  24                             19
  67 //                    |                           |
  68 //                  23 22-----------------------21 20
  69
  70 struct AccessibilityFocusRing {
  71   // Construct an AccessibilityFocusRing that outlines a rectangular object.
  72   static AccessibilityFocusRing CreateWithRect(
  73       const gfx::Rect& bounds, int margin);
  74
  75   // Returns a ring where 0.0 returns r1, 1.0 returns r2, and any number
  76   // in-between interpolates linearly between them.
  77   static AccessibilityFocusRing Interpolate(
  78       const AccessibilityFocusRing& r1,
  79       const AccessibilityFocusRing& r2,
  80       double fraction);
  81
  82   // Construct an AccessibilityFocusRing that outlines a paragraph-shaped
  83   // object.
  84   static AccessibilityFocusRing CreateWithParagraphShape(
  85       const gfx::Rect& top_line,
  86       const gfx::Rect& body,
  87       const gfx::Rect& bottom_line,
  88       int margin);
  89
  90   gfx::Rect GetBounds() const;
  91
  92   gfx::Point points[36];
  93 };
  94
  95 }  // namespace chromeos
  96
  97 #endif  // CHROME_BROWSER_CHROMEOS_UI_ACCESSIBILITY_FOCUS_RING_H_