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Salvendy,M.
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Smith(Eds.
):HumanInterface,PartII,HCII2011,LNCS6772,pp.
305–314,2011.
Springer-VerlagBerlinHeidelberg2011DodgingWindowInterferencetoFreelyShareAnyOff-the-ShelfApplicationamongMultipleUsersinCo-locatedCollaborationShinichiroSakamoto,MakotoNakashima,andTetsuroItoDepartmentofComputerScienceandIntelligentSystems,OitaUniversity700Dannoharu,Oita-shi,Oita-ken,870-1192,Japan{v0753035,nakasima,ito}@oita-u.
ac.
jpAbstract.
Amethodofdodgingwindowinterferenceisdescribedforallowingmultipleuserstofreelyshareanyoff-the-shelfsingle-userapplicationinco-locatedcollaborationutilizingashareddevice.
Thismethodisindispensablefortransparentlyrealizingapplicationsharinginlighteffortwithacentralizedarchitecturebyusingasurrogatewindowwhichisamimicoftheoriginalapplication'swindow.
Althoughtheoriginalapplicationshouldprocessanyeventonthesurrogatewindow,windowinterferencecouldbecausedbyoverlappingthelocationofaneventwiththesurrogatewindowandthentheeventcannotbeprocessed.
Toavoidwindowinterferenceweformulatethemethodbasedonquadrant-basedwindowpositioning,inwhichtheoriginalapplication'swindowisdynamicallyrepositionedfordisplayingonlyonequadrantofthiswindowinonecornerofthescreenarea.
Theavailabilityoftheproposedmethodwascertifiedandtheusabilitywasclarifiedinco-locatedcollaborationinauniversitylaboratory.
Keywords:Dodgingwindowinterference,windowpositioning,collaboration,applicationsharing,CSCW,centralizedarchitecture,screen-sharingsystem.
1IntroductionManywaysofsharinganyoff-the-shelfsingle-userapplicationamongmultipleusersarewelldocumentedforcomputer-supportedcooperativework(CSCW).
Acentralizedarchitectureisemployedinmostavailablescreen-sharingsystems(e.
g.
,[5]and[7]).
Theapplicationsharingisachievedbycentralizinganoriginaloff-the-shelfsingle-userapplication(an'originalapplication'inshort)andeventoccurrencesontoonePC,andbycopyingthewindowimageoftheoriginalapplicationoneachuser'sPC.
Thisarchitecturecantransparentlyrealizeapplicationsharingindistributedcollaborationwithnospecificeffort,i.
e.
,withoutchangingthesourcecodeoftheoriginalapplicationforreplicatingit.
However,theutilizationofthisarchitectureinco-locatedcollaboration,wheremultipleusersgatheraroundashareddevice,e.
g.
,atabletopdisplay,hasnotbeenstudiedindepth.
Acentralizedarchitecturehasthebenefitofsupportingco-locatedcollaborationbyallowingeachusertoutilizetheoriginalapplicationviaitssurrogatewindowin306S.
Sakamoto,M.
Nakashima,andT.
Itohis/herpreferredlocationandorientation[1].
Here,eachofthesurrogatewindowsworksasamimicoftheoriginalapplication'swindow(an'originalwindow'inshort)whiledisplayingitscopiedwindowimage.
Eachuserinitiatesanyevent,suchasclickingamousebutton,draggingamouse,pressingakey,etc.
,onhis/herownsurrogatewindow,notontheoriginalwindow.
Theoriginalwindowshould,however,beonthetopofotherwindowsinordertoreceiveeveryeventonitssurrogatewindow.
Theeventsonthesurrogatewindowaretheninterferedwithbytheoriginaltopwindow.
Inordertofreelysharetheoriginalapplicationamongmultipleuserswithoutcausingsuchinterference,itiscrucialthattheoriginalwindowisrepositionedtoanappropriateplaceonthescreenareaaccordingtothelocationoftheevent.
Weproposeanovelmethodofdodgingwindowinterferencetofreelyshareanyoff-the-shelfsingle-userapplicationamongmultipleusersinco-locatedcollaboration.
Thismethoddynamicallyrepositionstheoriginalwindowsothatthiswindowdodgestheinterferencewithitssurrogatewindows,allowingtheoriginalapplicationtoreceivetheeventsonthesurrogatewindowsatanygiventime.
Toachievethis,themethodrealizesquadrant-basedwindowrepositioningwhichdrawsonlyonequadrantoftheoriginalwindowamongfourquadrantsincludingthecorrespondinglocationoftheeventontheoriginalwindowastheircommonorigin.
Sincetheoriginalwindowhasasquareshape,itenablesustoprovethatatleastonequadrantexiststherebyavoidingwindowinterferenceeveniftheeventoccursatanylocationonanysurrogatewindowwhenthesizeoftheoriginalwindowissmallerthanthatofthescreenarea.
Itisalsopossibletominimizetheeffortrequiredtorepositiontheoriginalwindowcausedbythelatereventswhenthedisplayedquadrantisfarawayfromtheeventlocationonthescreenareatoavoidwindowinterference.
Therestofthispaperisorganizedasfollows:Theproblemsofpreviousapplication-sharingsystemsinco-locatedcollaborationarediscussedinSection2.
Therequirementsandthequadrant-basedwindowrepositioningoftheproposedmethodaredescribedinSection3.
WeestimatedtheavailabilityofourmethodinSection4andclarifiedtheusabilityofthemethodinco-locatedcollaborativeworkinSection5,whereweimplementedourmethodintoanapplication-sharingsystem,CollaboTray[1]employingacentralizedarchitecture.
2ApplicationSharinginCollaborationThissectiondescribespreviousscreen-sharingsystemsandanadvancedapplication-sharingsystembasedonacentralizedarchitecture.
Wealsodiscusstheproblemstheyhaveinco-locatedcollaboration.
2.
1Application-SharingSystemsForapplicationsharing,screen-sharingsystemshavebeenusedinpracticeforalmosttwentyyears,e.
g.
,PCAnyWhere[7],NX[4],andVNC[5].
Amongthemtheopen-sourcescreen-sharingsystemVNCisutilizedinmanysystemsforapplicationsharing(e.
g.
[2],[8],and[9]).
Thosesystemscanallowtheuserstoshareanyoff-the-shelfapplicationviaitsoriginalwindowandsurrogatewindowswithoutsharingthewholescreenononePC.
AVNC-basedtoolkitforwindowmanagingonX-windowsystem,DodgingWindowInterferencetoFreelyShareAnyOff-the-ShelfApplication307Ametista[6],allowsausertorotatethewindowimageastheusersneedinco-locatedcollaboration[3].
ThoseVNCsystems,however,haveaproblemthattheusersofthesurrogatewindowsarenotabletoinitiateanyeventastheuseroftheoriginalwindowisoperatingtheoriginalapplication.
Anapplication-sharingsystem,CollaboTray[1],candealwiththeaboveproblembymakingeachoftheusersutilizethesurrogatewindowwhileitsoriginalwindowismadeinvisibletodisallowuseofitbyanyuser.
ACollaboTraycentralizesanoriginalapplicationononlyonePCanddecouplesthedrawingofthesurrogatewindowofanorignalwindowfromtheprocessingofanyeventonthesurrogatewindow.
AnyoriginalCollaboTray,whichisloadedwithanoriginalapplication,canyielditscloneCollaboTrayseachofwhichmanagesinherentlythesamesurrogatewindowastheoriginalCollaboTray.
TheCollaboTrayusestheoriginalwindowinadifferentwayfromthepreviousscreen-sharingsystemsandhasadvantageofallowingtheuserstosharetheoriginalapplicationinanyorientationandtime.
Figure1illustratesthebasicapproachofrealizingapplicationsharinginco-locatedcollaborationwithacentralizedarchitecture,whereanoriginalwindowanditstwosurrogatewindowsAandBexist.
InutilizationofVNC,ifownershipoftheoriginalwindowisdisallowedbyanyuserlikeCollaboTrays,theuserscaninitiateanyeventbytakingturnsamongthemselveswhenutilizingtheoriginalapplicationviatheirsurrogatewindows.
However,acommonproblemarisesinapplicationsharingbyVNCandCollaboTrayswhentheoriginalwindowoverlapswithitssurrogatewindowsasshowninthefigure.
Eveniftheoriginalwindowisinvisible,theoriginalwindowneedstobeontopofthesurrogatewindowstoreceiveanyeventonthem.
Theproblemisthatthesurrogatewindowownedbyausershouldalsobeontopoftheoriginalwindowtoallowhim/hertooperatetheoriginalapplication.
Thiscontradictioncauseswindowinterferencebetweentheoriginalwindowanditssurrogatewindow.
Notethateachofthesurrogatewindowsdonotinterferewitheachothersinceneitherisrequiredtobeontopoftheothersurrogatewindowwhenitsuserinitiatesanyevent.
ThecorrespondinglocationoftheeventSurrogatewindowAScreenareaSurrogatewindowBThelocationofaneventOriginalwindowFig.
1.
Applicationsharinginco-locatedcollaboration2.
2WindowInterferenceinCo-locatedCollaborationThetwocasesofwindowinterferenceareillustratedinFig.
1.
Inthefigure,thelocationofeacheventonthesurrogatewindowsisrepresentedbyafilledcircularor308S.
Sakamoto,M.
Nakashima,andT.
Itotriangularshapedmark.
Theunfilledonescorrespondtothelocationoftheeventontheoriginalwindow.
ForsurrogatewindowA,theareaincludingthecorrespondinglocationoftheeventontheoriginalwindowisoverlappedwiththissurrogatewindow.
WhentheuserinitiatestheeventonthesurrogatewindowA,theoriginalwindowisinterferedwithbysurrogatewindowAastheuserisinitiatinganeventonthesurrogate,theoriginalwindowisunabletogetonthetop,andthustheeventcannotbesenttotheoriginalapplication.
Conversely,forthesurrogatewindowB,theareathatincludesthelocationoftheeventonthissurrogatewindowisoverlappedwiththeoriginalwindow.
Whentheeventissenttotheoriginalapplication,theoriginalwindowgetsontopofsurrogatewindowBandthustheuserofsurrogatewindowBcannotinitiatehis/hernextevent.
Inadditiontotheabove,thereisanotherconcernaboutthefeatureofthemousemoving.
IfauserusesastandardUSBmouse,thelocationofthemousecursoronthescreenareaisupdatedevery8msec.
Foranyevent,thelocationofthenexteventmayjumptotheplaceontheoriginalwindowcausingthekindofinterferenceseeninsurrogatewindowBinFig.
1.
Thiscanoccureveniftheoriginalwindowisplacedwhereitcanavoidwindowinterference.
3DodgingWindowInterferenceThissectiondescribesthemethodofdodgingwindowinterferencebyusingquadrant-basedwindowrepositioning.
Wefirstspecifytherequirementstoavoidwindowinterferenceandthenformulatethemethodtomeettheserequirements.
3.
1RequirementsTherearetworequirementstoavoidthewindowinterferencementionedinSection2.
2:(a)toavoidthephysicaloverlappingbetweentheoriginalwindowanditssurrogatewindowtoalloweachothertogetontopifneeded,and(b)toavoidwindowinterferencebyanyfastmovementofthemousecursor.
Theformerleadsthefollowingconditionstobesatisfied:Ca1:Thecorrespondinglocationoftheeventontheoriginalwindowisoutsideitssurrogatewindowonwhichtheeventoccurs.
Ca2:Thelocationoftheeventonasurrogatewindowisoutsideitsoriginalwindow.
Thelatterrequirementispossiblyavoidedbysatisfyingthefollowingcondition:Cb:Theoriginalwindowstaysasfarawayfromthelocationofaneventonitssurrogatewindowaspossible.
ConditionsCa1andCa2leadustounderstandthatonlythesmallestpossibleareaoftheoriginalwindowhastobedisplayed,whichincludesthecorrespondinglocationoftheevent.
ForconditionCb,sincethescreenareahasasquareshape,oneofthefourcornersofthescreenareaisthefurthestfromthelocationofanyevent.
Giventhesefacts,wedeviseawayofquadrant-basedwindowrepositioning,whichselectsaquadrantoftheoriginalwindowwiththecorrespondinglocationoftheeventasitsDodgingWindowInterferencetoFreelyShareAnyOff-the-ShelfApplication309origin,anddisplaythisquadrantonthecornerofthescreenarea,thussatisfyingtheaboveconditions.
3.
2Quadrant-BasedWindowPositioningFig.
2showsanexampleofdodgingwindowinterferenceforthecaseofsurrogatewindowAinFigure1,inwhichtheoriginalwindowisrepositionedtothetoprightcornerofthescreenarea.
Onlythethirdquadrant,i.
e.
,Q3,oftheoriginalwindowisselectedtobedisplayedwithlowopacityonthescreenarea,wherefourquadrantsincludingthecorrespondinglocationoftheeventastheircommonoriginexist.
Wheneachofthetwoquadrants,Q2andQ4,isselected,theoriginalwindowcanberepositionedtothebottomrightandthetopleftcorners,respectively,asshowninthedashedsquareinthefigure.
Theoriginalwindowis,however,thefurthestfromthelocationoftheeventwhenQ3isselected.
SelectingQ3satisfiesCa1,Ca2,andCb.
IfQ1isselected,theoriginalwindowisrepositionedtothebottomleftcornerofthescreenareabutconditionCa2isnotsatisfied.
OriginalwindowSurrogatewindowAScreenareaOriginalwindowOriginalwindowSLSRSBSTOriginalwindowQ1Q4WLWRWBWTQ2Q3Fig.
2.
DodgingwindowinterferenceWeherecallaquadrantQi(i=1,2,3,4)oftheoriginalwindowanavailablequadrantif,QicanbedisplayedsoastosatisfyconditionsCa1andCa2bypositioningitsoriginonthecornerofthescreenareaintheoppositedirectionofQi.
Theoverallprocessofdodgingwindowinterferencebetweentheoriginalanditssurrogatewindowissummarizedasfollows:Step1:Dividetheoriginalwindowintofourquadrantswiththecorrespondinglocationoftheeventastheircommonorigin.
Step2:Findallavailablequadrantsfromthosefourquadrants.
Step3:SelectonequadrantQifromamongtheabovequadrants,whichsatisfiesconditionCb.
Step4:RepositiontheoriginalwindowsoastoonlydisplayQionthescreenarea.
Iftheaboveprocesscanfindanavailablequadrant,wecansaythattheoriginalwindowcanavoidwindowinterferencewithitssurrogatewindow.
Althoughthe310S.
Sakamoto,M.
Nakashima,andT.
Itoavailablequadrantcanbeoverlappedwiththesurrogatewindowinstep4,theutilizationofthesurrogatewindowdosenotinterferewiththequadrantbymakingitinvisible.
Letusprovetherobustnessoftheaboveprocessinfindingavailablequadrants.
AsshowninFig.
2,letWL,WR,WTandWBdenotethedistanceofthecorrespondinglocationoftheeventontheoriginalwindowfromtheleft,right,topandbottomedgesofthewindow,respectively.
AlsoletSL,SR,STandSBdenotethedistanceofthelocationoftheeventonthesurrogatewindowfromtheleft,right,topandbottomedgesofthescreenarea,respectively.
Supposethatboththesizeoftheoriginalandsurrogatewindowsaresmallerthanthescreenareainwidthandinheight,i.
e.
,WL+WRpcanywhere.
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UltraVNC,http://www.
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