Gecko vbufBackend: implement a replacement AccessibleObjectFromEvent …

…that actually works when called from within a 64 bit process. Technically, AccessibleObjectFromWindow is the actual function with the bug, though AccessibleObjectFromEvent calls it.

The new AccessibleObjectFromEvent_fixed only uses custom code where absolutely necessary. It in fact is a macro that only on 64 bit is defined as the custom function, otherwise its just AccessibleObjectFromEvent. Plus, the custom function only does the custom code if the current thread and the thread for the window are the same, otherwise it calls the original AccessibleObjectFromEvent.
The custom code just does the standard wm_getobject, ObjectFromLResult, tries accChild. Pretty much exactly what its clear AccessibleObjectFromEvent/AccessibleObjectFromWindow does. I have no idea why AccessibleObjectFromWindow fails.
In short all this means that virtualBuffers are no longer blank in 64 bit builds of Mozilla Gecko applications.
Fixes #1454.

nvdaHelper/vbufBackends/gecko_ia2/gecko_ia2.cpp

@@ -31,6 +31,41 @@ using namespace std;
 
 #define NAVRELATION_NODE_CHILD_OF 0x1005
 
+//An implementation of AccessibleObjectFromEvent that works  for a window in the same thread, when in a 64 bit process
+//Technically AccessibleObjectFromWindow seems to be the broken function 
+HRESULT _AccessibleObjectFromEvent_fixed(HWND hwnd, long objectID, long childID, IAccessible** pacc, VARIANT* varChild) {
+	if(GetWindowThreadProcessId(hwnd,NULL)!=GetCurrentThreadId()) {
+		return AccessibleObjectFromEvent(hwnd,objectID,childID,pacc,varChild);
+	}
+	//SendMessage is fine as we are in the same thread as the window
+	LRESULT l=SendMessage(hwnd,WM_GETOBJECT,0,objectID);
+	if(l==0) {
+		return E_FAIL;
+	}
+	if(ObjectFromLresult(l,IID_IAccessible,0,(void**)pacc)!=S_OK) {
+		return E_FAIL;
+	}
+	(*varChild).vt=VT_I4;
+	(*varChild).lVal=childID;
+	IDispatch* childDisp=NULL;
+	if((*pacc)->get_accChild(*varChild,&childDisp)==S_OK) {
+		IAccessible* childPacc=NULL;
+		if(childDisp->QueryInterface(IID_IAccessible,(void**)&childPacc)==S_OK) {
+			(*pacc)->Release();
+			*pacc=childPacc;
+			(*varChild).lVal=0;
+		}
+		childDisp->Release();
+	}
+	return S_OK;
+}
+
+#ifdef _WIN64
+#define AccessibleObjectFromEvent_fixed _AccessibleObjectFromEvent_fixed
+#else
+#define AccessibleObjectFromEvent_fixed AccessibleObjectFromEvent
+#endif
+
 HWND findRealMozillaWindow(HWND hwnd) {
 	LOG_DEBUG(L"Finding real window for window "<<hwnd);
 	if(hwnd==0||!IsWindow(hwnd)) {
@@ -66,7 +101,7 @@ IAccessible2* IAccessible2FromIdentifier(int docHandle, int ID) {
 	IAccessible2* pacc2=NULL;
 	VARIANT varChild;
 	LOG_DEBUG(L"calling AccessibleObjectFromEvent");
-	if((res=AccessibleObjectFromEvent((HWND)docHandle,OBJID_CLIENT,ID,&pacc,&varChild))!=S_OK) {
+	if((res=AccessibleObjectFromEvent_fixed((HWND)docHandle,OBJID_CLIENT,ID,&pacc,&varChild))!=S_OK) {
 		LOG_DEBUG(L"AccessibleObjectFromEvent returned "<<res);
 		return NULL;
 	}
@@ -937,6 +972,9 @@ void CALLBACK GeckoVBufBackend_t::renderThread_winEventProcHook(HWINEVENTHOOK ho
 	if(childID>=0||objectID!=OBJID_CLIENT) {
 		return;
 	}
+	if(eventID==EVENT_OBJECT_FOCUS) {
+		LOG_INFO(L"focus event: hwnd "<<hwnd<<L", objectID "<<objectID<<L", childID "<<childID);
+	}
 	LOG_DEBUG(L"winEvent for window "<<hwnd);
 	hwnd=findRealMozillaWindow(hwnd);
 	if(hwnd==0) {

user_docs/en/changes.t2t

@@ -96,6 +96,7 @@ Highlights of this release include major improvements concerning punctuation and
 - NVDA no longer becomes worse at guessing color names the more colors it announces.
 - In Internet Explorer and other MSHTML controls, fixed the inability to read parts of rare pages which contain iframes marked with an ARIA role of presentation. (#1569)
 - In Internet Explorer and other MSHTML controls, fixed a rare problem where the focus kept bouncing infinitely between the document and a multi-line editable text field in focus mode. (#1566)
+- Browse mode Documents no longer appear blank in 64 bit Mozilla Gecko applications. (#1454)
 
 
 == Changes for Developers ==