UXP/accessible/windows/msaa/nsWinUtils.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:expandtab:shiftwidth=2:tabstop=2:
 */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsWinUtils.h"

#include "Compatibility.h"
#include "DocAccessible.h"
#include "nsAccessibilityService.h"
#include "nsCoreUtils.h"

#include "mozilla/Preferences.h"
#include "nsArrayUtils.h"
#include "nsIArray.h"
#include "nsICSSDeclaration.h"
#include "nsIDocument.h"
#include "nsIDocShellTreeItem.h"
#include "mozilla/dom/Element.h"
#include "nsXULAppAPI.h"

using namespace mozilla;
using namespace mozilla::a11y;
using mozilla::dom::Element;

// Window property used by ipc related code in identifying accessible
// tab windows.
const wchar_t* kPropNameTabContent = L"AccessibleTabWindow";

/**
 * WindowProc to process WM_GETOBJECT messages, used in windows emulation mode.
 */
static LRESULT CALLBACK WindowProc(HWND hWnd, UINT msg,
                                   WPARAM wParam, LPARAM lParam);

bool nsWinUtils::sWindowEmulationStarted = false;

already_AddRefed<nsIDOMCSSStyleDeclaration>
nsWinUtils::GetComputedStyleDeclaration(nsIContent* aContent)
{
  nsIContent* elm = nsCoreUtils::GetDOMElementFor(aContent);
  if (!elm)
    return nullptr;

  // Returns number of items in style declaration
  nsCOMPtr<nsPIDOMWindowInner> window = elm->OwnerDoc()->GetInnerWindow();
  if (!window)
    return nullptr;

  ErrorResult dummy;
  nsCOMPtr<nsICSSDeclaration> cssDecl;
  nsCOMPtr<Element> domElement(do_QueryInterface(elm));
  cssDecl = window->GetComputedStyle(*domElement, EmptyString(), dummy);
  nsCOMPtr<nsIDOMCSSStyleDeclaration> domDecl = do_QueryInterface(cssDecl);
  dummy.SuppressException();
  return domDecl.forget();
}

bool
nsWinUtils::MaybeStartWindowEmulation()
{
  // Register window class that'll be used for document accessibles associated
  // with tabs.
  if (IPCAccessibilityActive())
    return false;

  if (Compatibility::IsJAWS() || Compatibility::IsWE() ||
      Compatibility::IsDolphin() ||
      XRE_IsContentProcess()) {
    RegisterNativeWindow(kClassNameTabContent);
    sWindowEmulationStarted = true;
    return true;
  }

  return false;
}

void
nsWinUtils::ShutdownWindowEmulation()
{
  // Unregister window call that's used for document accessibles associated
  // with tabs.
  if (IsWindowEmulationStarted()) {
    ::UnregisterClassW(kClassNameTabContent, GetModuleHandle(nullptr));
    sWindowEmulationStarted = false;
  }
}

void
nsWinUtils::RegisterNativeWindow(LPCWSTR aWindowClass)
{
  WNDCLASSW wc;
  wc.style = CS_GLOBALCLASS;
  wc.lpfnWndProc = WindowProc;
  wc.cbClsExtra = 0;
  wc.cbWndExtra = 0;
  wc.hInstance = GetModuleHandle(nullptr);
  wc.hIcon = nullptr;
  wc.hCursor = nullptr;
  wc.hbrBackground = nullptr;
  wc.lpszMenuName = nullptr;
  wc.lpszClassName = aWindowClass;
  ::RegisterClassW(&wc);
}

HWND
nsWinUtils::CreateNativeWindow(LPCWSTR aWindowClass, HWND aParentWnd,
                               int aX, int aY, int aWidth, int aHeight,
                               bool aIsActive)
{
  HWND hwnd = ::CreateWindowExW(WS_EX_TRANSPARENT, aWindowClass,
                                L"NetscapeDispatchWnd",
                                WS_CHILD | (aIsActive ? WS_VISIBLE : 0),
                                aX, aY, aWidth, aHeight,
                                aParentWnd,
                                nullptr,
                                GetModuleHandle(nullptr),
                                nullptr);
  if (hwnd) {
    // Mark this window so that ipc related code can identify it.
    ::SetPropW(hwnd, kPropNameTabContent, (HANDLE)1);
  }
  return hwnd;
}

void
nsWinUtils::ShowNativeWindow(HWND aWnd)
{
  ::ShowWindow(aWnd, SW_SHOW);
}

void
nsWinUtils::HideNativeWindow(HWND aWnd)
{
  ::SetWindowPos(aWnd, nullptr, 0, 0, 0, 0,
                 SWP_HIDEWINDOW | SWP_NOSIZE | SWP_NOMOVE |
                 SWP_NOZORDER | SWP_NOACTIVATE);
}

LRESULT CALLBACK
WindowProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
  // Note, this window's message handling should not invoke any call that
  // may result in a cross-process ipc call. Doing so may violate RPC
  // message semantics.

  switch (msg) {
    case WM_GETOBJECT:
    {
      // Do explicit casting to make it working on 64bit systems (see bug 649236
      // for details).
      int32_t objId = static_cast<DWORD>(lParam);
      if (objId == OBJID_CLIENT) {
        DocAccessible* document =
          reinterpret_cast<DocAccessible*>(::GetPropW(hWnd, kPropNameDocAcc));
        if (document) {
          IAccessible* msaaAccessible = nullptr;
          document->GetNativeInterface((void**)&msaaAccessible); // does an addref
          if (msaaAccessible) {
            LRESULT result = ::LresultFromObject(IID_IAccessible, wParam,
                                                 msaaAccessible); // does an addref
            msaaAccessible->Release(); // release extra addref
            return result;
          }
        }
      }
      return 0;
    }
    case WM_NCHITTEST:
    {
      LRESULT lRet = ::DefWindowProc(hWnd, msg, wParam, lParam);
      if (HTCLIENT == lRet)
        lRet = HTTRANSPARENT;
      return lRet;
    }
  }

  return ::DefWindowProcW(hWnd, msg, wParam, lParam);
}