flashcannonballlab.docx

flashcannonballlab.docx

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flashcannonballlab

Flash5/MX:

CannonballlabUPDATESFORFLASH8

NOTE:

IhavemadeupdatestofitFlash8.Thechangesare

∙thattheuseofthevarnameforinputanddynamictextboxesdoesnotworkwiththeup-to-dateFlashplayers.Instead,theinstancenamemustbesetandthe.textpropertyused.

∙MyeducationalversionofFlash8didnotappeartohaveSoundsasoneoftheCommonLibraries.Idescribealternativewaystogetsounds.

∙Thestartdragfunctionwasusedinplaceofthestartdragmethod.

Animation（movementofimagesonthescreen）canbeproducedusingFlashinseveraldifferentways.Forthisapplication,yourcodewillsimulatetheballisticsofacannonballleavingthecannon,travelingina[parabolic]arc,andeitherhittingthegroundorhittingatarget.YouwillNOTuseframeanimation:

creategraphicsofacannonballindifferentpositionsinasequenceofframes.Youwillnotusetweening.

Thefollowingfigureshowstheapplicationafterafiringofthecannon.Noticethatthecannonballhasfallenontheground.Theapplicationbeginswiththecannonballoff-stage.YourcodewillmovetheballtotheendofthecannonwhentheFIREbuttonispressed.

Hereiswhatthescreenlookslikeafterahit（achievedbecausetheplayerhaschangedtheangleofthecannonandthespeed）.

Herearethecriticalfeaturesrequiredtoimplementthisapplication:

1.Calculationoftheflightpathofthecannonballbasedontheinitialspeed,theangleofthecannonandtheeffectofgravity.Thecriticalconceptforballisticsinvolvesseparatingtheinitialmotionofthecannonballintoverticalandhorizontalcomponents（alsoknownasresolvingthevectors）.Thecannonballleavesthecannonatanangle.Inthesimplifiedworldwesimulatehere（noairresistance,forexample）thehorizontalmotioncontinuesatthesamevelocity（speed）.Theverticalmotion,however,isaffectedbygravity.Thisiswhatcausesthearc（theparabolic）path.Theequationsforthisturnouttobejustafewlinesofcodeinthefunctionthathandlestheon（release）eventfortheFirebuttonandafewmoreinascriptinframesonthemovietimeline.

2.Awaytomakeincrementalchangesinthepositionoftheballtosimulateflight.ThiswillbedonebyusingActionScripttowritewhataretermedframeactionstomakeadjustmentstothepositionofmovieclipwecallball.

3.Awaytocheckifthetargethasbeenhitoriftheballhasreachedgroundlevel.Itturnsoutthatthisisdoneinscriptintwodifferentplaces.Thecodetodetermineiftheballhashitthegroundisdoneinaframeaction.ThecodetodetermineiftheballhashitthetargetisdoneinwhatistermedtheenterFrameclipeventofthetarget.

4.Awayfortheplayertocontrolthepathbychangingthespeedandtheangleandtomovethetarget.Tomakethisagame,weneedtoprovideawaytogetinputfromtheplayer.WedothisusingInputTextfields.Thevaluestheplayerputsinthesefieldsareusedinthecalculationofthepath.

Note:

inourprojectthenameofthetargetinstanceistarget1.Thisistoinspireyoutothinkaboutmoreanddifferenttargets.Itcouldalsohavebeentarget.Inanycase,thereisnorelationshipbetweenthisspecificinstanceandtheTellTargetconstructionusedinolderversionsofFlash,butgenerallyunnecessaryinFlash5.

Thesegraphicsarequitestylized.Afteryougetsomethingworking,youcanenhancethelook-and-feeloftheapplication.

Preparethefollowingassymbolsandthencreateinstancesonstage.Givethesymbolsthenamesindicated（usingtheInstancepanelinFlash5andthePropertiespanelinFlashMX）.Youmayaskwhy,withthegraphicsbeingsosimpleandonlyoneofeachthing,doIhavetomakeeachoneamovieclip?

Theansweristhatthisapproachmakesseveralthingspossible:

youcanrefertothesymbolsbyname,refertoandchangepropertiessuchas_x,_y,and_rotation,usethehitTestmethodandyoucanwriteeventhandlers.Thelattermeansyoucanarrangeforsomethingtohappeneachframeandsomethingtohappenwhentheplayerpressesdownorreleasesthemouse.Notetheregistrationpoint（alsocalledtheoriginorthenominalposition）forthegraphics.Positionandmovement,includingrotation,isintermsofthisregistrationpointshownascross-hairswhenyouselecttheobject.

Symbolname&type

Instancename

Graphics

Associatedevents,usage

ballmovieclip

ball

Circle,registrationpointupperleftcorner（notcenter）

Propertiesreferencedandmodifiedbyframescriptsandeventhandlers.

cannonmovieclip

cannon

Horizontalline,registrationpointleftend

_xand_yreferencedtopositionball.

_rotationchangedbasedonanInputtextfield;referencedtodetermineangle

groundmovieclip

ground

Two（thick,horizontal）lines,registrationpointmid-point.

_yreferencedduringflight

targetmovieclip

target1

Thereisonly1target,butyoumaychoosetoaddmore.

Rectangle,withregistrationpointatlowerleftcorner

Clipevent（enterFrame）usedfordetectingahit.

Clipeventsmousedownandmouseupusedindragging

firebuttonbutton

NeedtoplaceDynamicTextfieldnamedcaptiononthebutton.

oval,withDynamictextfield.

on（release）isacallto_root.firecannonlocatedinthefirstframe,actionslayer

Becauseofhowwewantthetargetrectangletotiltwhenitishit,youneedtomakesuretherectangle'sregistrationpointisthelowerleftcorner,asshownbelow:

Thiswillcausetherectangletopivotfromthelowerleftcorner.Donotthinkforamomentthatweknewthisaheadoftime.

Youneedtoputonthescreenthe4textfields:

REMEMBER:

forFLASH8,settheinstancenameNOTthevarnamefortheInputtextfields.

Name

Contents

Type

Usage

Speed

Static

Labelnextfield

speed

Initially10

Input

Playertypesinnewspeed

Degrees

Static

Labelnextfield

anglein

Initially45

Input

Playertypesinnewangle.

Weproposethatyouprogramthisapplicationinstages.Thisgivesyouachancetotesttheapplicationasyougoalong.

StageI.Maketheballmoveinanarconthescreen.

StageII.Addthetestforhittingthetarget.

StageIII.Addthecolorchangeandthesoundwhentheballhitsthetarget.

StageIV.Addthefeaturetomove（drag）thetarget.

StageV.Addthetargetleaningover.

CAUTION:

Whenyoucreateanewkeyframe,unlessyoucreateablankkeyframe,Flashwillcopyallthecontentthatwasinthepreviouskeyframe.Thisgenerallyiswhatyouwant.Ifyoulatergobackandaddsomethingtoanearlierframe,thiscontentdoesnotautomaticallygetaddedtotheexistingframesthatfollow.Ifyouwantthenewmaterialtobepartofotherframes,youmustdoadditexplicitly.Thecopyandpaste-in-placecommandscanbeused.Thisalsoappliestoobjectactioncode.Ifyouaddorchangeobjectactioncodeinoneframe,youmustdothesamethingfortheotherframes,ifthatiswhatyouwant.

StageI.Therequirementsforcodingdivideintowhatisdonetosetupthemotionoftheballandwhatisdonetomovetheballiterativelyalongitspath.ThesetupisdoneinresponsetopressingthebuttonlabeledFIRE.Theiterativemovementisdoneinframeactions.

DisplaytheActionspanel（Flash5:

Window/Actions）orExpandit（FlashMXandFlash8）.IntheControldropdownmenu,makesureEnableSimpleButtonActionsisNOTchecked.Totesttheprogram,youmayneedtochangethistobeingchecked.ClickontheFirebuttoninstanceonthestage.IntheActionspanel,clickthearrowtogettoExpertModeandtypein:

on（release）{

_root.firecannon（）;

}

Thismeans:

whenthebuttonisreleased（thatis,theplayerpressesdownwiththemouseoverthebuttonandthenreleasesit）,callthefunctionfirecannonthatisdefinedinthemainmovie.Wecouldputthecodehere,butitisconsideredagoodpracticetocentralizethecode.Wewillgiveanexampleofanotherwaylater.Thefirecannonfunctionwillbedefinedinthefirstframe.Beforedoingthis,youneedtodosomesetupoflayersandframes.

Namethefirstandonlylayerofthemainmovieboard.Addanewlayerandnameitactions.Youwillputallthecodeintheactionslayer.Addanotherlayerandcallitlabels.Youneedtohave3keyframesineachlayer.Thismeansyouneedtoaddtwokeyframestoeachone.Flash8:

Insert/Timeline/Keyframe.

Clickinthesecondframeofthelabelslayer.Flash5:

intheFramespanel（Window/Panels/Frame）,givethisframethelabelcontinue.FlashMXandFlash8:

inthepropertiespanel,typeincontinueintheFrametextbox.Aflagwillappearintheframe.

Youwillnowputcodeinthefirstframeoftheactionslayer.Thecodesetsupvariablesanddefinesthefirecannonfunction.Theinflightvariablewillbetrueorfalsedependingonwhethertheballisin-flight.Asyouwillsee,thefirecannonroutinesetsinflighttobetrue.Watchoutforwhereitissettofalse.Thenow,then,andelapsedvariablesareusedtocalculatethetime.NoticethatthenissetinfirecannonbyacalltogetTimer.

Recallfromtheintroductionthatthecharacteristicarcofprojectilemotionoccursbecausethehorizontalvelocityremainsthesamebuttheverticalvelocitychanges.Theballisshotfromthecannonatanangle.Yourcodewilldeterminetheinitialhorizontalandverticalcomponentsoftheball'smotionusingtrigonometry.

Thevariablehspeedissettothehorizontalcomponentinfirecannon.Youneedtwovariablesfortheverticalcomponentbecauseitischangingduetotheeffectsofgravity.Thevariablegravityholdsthevalueofgravityper1/12thofasecond.（Thisappearsmoreseriousthanitreallyis.Theunitscouldbewhateverwewant,butthisvalueseemstoworkoutwell.）Thevspeed1variablewillhold