1 // Copyright (c) 2012 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 CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_FOCUS_ONLY_H_ 6 #define CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_FOCUS_ONLY_H_ 7 8 #include "content/renderer/accessibility/renderer_accessibility.h" 9 10 namespace content { 11 12 // This is an accsessibility implementation that only handles whatever 13 // node has focus, ignoring everything else. It's here because on Windows 8, 14 // we need to use accessibility APIs to tell the operating system when a 15 // touch should pop up the on-screen keyboard, but it's not worth the 16 // performance overhead to enable full accessibility support. 17 // 18 // Here's how the on-screen keyboard works in Windows 8 "Metro-style" apps: 19 // 20 // 1. The user touches a control. 21 // 2. If the application determines focus moves to an editable text control, 22 // it sends a native focus event, pointing to a native accessibility object 23 // with information about the control that was just focused. 24 // 3. If the operating system sees that a focus event closely follows a 25 // touch event, AND the bounding rectangle of the newly-focused control 26 // contains the touch point, AND the focused object is a text control, 27 // then Windows pops up the on-screen keyboard. In all other cases, 28 // changing focus closes the on-screen keyboard. 29 // 30 // Alternatively: 31 // 1. The user touches a text control that already has focus. 32 // 2. The operating system uses accessibility APIs to query for the 33 // currently focused object. If the touch falls within the bounds of 34 // the focused object, the on-screen keyboard opens. 35 // 36 // In order to implement the accessibility APIs with minimal overhead, this 37 // class builds a "fake" accessibility tree consisting of only a single root 38 // node and optionally a single child node, representing the current focused 39 // element in the page (if any). Every time focus changes, this fake tree is 40 // sent from the renderer to the browser, along with a focus event - either 41 // on the child, or on the root of the tree if nothing is focused. 42 // 43 // Sometimes, touching an element other than a text box will result in a 44 // text box getting focus. We want the on-screen keyboard to pop up in those 45 // cases, so we "cheat" more and always send the dimensions of the whole 46 // window as the bounds of the child object. That way, a touch that leads 47 // to a text box getting focus will always open the on-screen keyboard, 48 // regardless of the relation between the touch location and the text box 49 // bounds. 50 class RendererAccessibilityFocusOnly : public RendererAccessibility { 51 public: 52 explicit RendererAccessibilityFocusOnly(RenderViewImpl* render_view); 53 virtual ~RendererAccessibilityFocusOnly(); 54 55 // RendererAccessibility implementation. 56 virtual void HandleWebAccessibilityEvent( 57 const blink::WebAXObject& obj, blink::WebAXEvent event) OVERRIDE; 58 virtual RendererAccessibilityType GetType() OVERRIDE; 59 60 // RenderView::Observer implementation. 61 virtual void FocusedNodeChanged(const blink::WebNode& node) OVERRIDE; 62 virtual void DidFinishLoad(blink::WebLocalFrame* frame) OVERRIDE; 63 64 private: 65 void HandleFocusedNodeChanged(const blink::WebNode& node, 66 bool send_focus_event); 67 68 int next_id_; 69 70 DISALLOW_COPY_AND_ASSIGN(RendererAccessibilityFocusOnly); 71 }; 72 73 } // namespace content 74 75 #endif // CONTENT_RENDERER_ACCESSIBILITY_RENDERER_ACCESSIBILITY_FOCUS_ONLY_H_ 76