Developmentstatus
TheearlyversionofthevideodisplayadapterreliedontheCPUtoprocessimageinformation,andtheCPUcontinuouslycalculatedthechangesofeachpixel.Informationisrequired,andthedataissenttotheframebufferofthevideocardthroughtheI/Obus.Theso-calledframebufferisamemorythatsavesscreenimagesallthetime.
Windows’graphicaluserinterfacedrasticallyincreasestheworkloadoftheCPUandI/Obus.InordertoreducetheburdenontheCPU,aconsiderableamountofgraphicsaccelerationmustbeobtained.ThesolutioncanonlybeinthevideoaccelerationcardAprocessingchipisadded,buttheCPUexecutesthegraphicsdeviceinterfacefunctioncall,andtheacceleratorcannotexecutethecall.ThegraphicsacceleratorreducestheI/ObusoftheCPU—itistousehard-wiredsomekeyGIDfunctionsofWindowsMethod.(GDIisanintegralpartofWindowstorealizethenecessarygraphicsfunctions).
Let’slookatacompleteworkprocess.TheWindowsapplicationprogramsendsagraphicsdeviceinterface(GDI),agraphicsfunctioncallrequest,andGDIrequiresthevideodrivertoperformthisfunction.Thedriversendstherequesttotheacceleratorforprocessing,andtheprocessorchiphandlesitthroughtheframebuffercontroller.Afterthescreendataiswrittentotheframebuffer,theframebuffercontrollersendsthedatatothememorydigital-to-analogconverter,wherethedataisconvertedintoananalogsignalforcontrollingtheCRT(cathoderaytube),ifthevideodrivercannotrecognizeitUponrequest,thegraphicsdeviceinterfaceusestheCPUandsystemRAMtoperformthisfunction.ThisiswhytheacceleratorcardcomeswithvariousdriverstosupportthemostpopularWindowsgraphicsapplications.
Inordertoobtainthebestdisplayconfiguration,thedrivershouldbeupdatedcontinuously.Whenaddingnewgraphicssoftwareormultimediasoftwaretothesystem,checkifthereisthelatestversionofthedriverfortheacceleratorcard.Itmaybeincludedinthesoftware.Ifnot,theycanbedownloadedfromthemanufacturer’sbulletinboardundernormalcircumstances,orcanbedownloadedfromapublicforumofanonlineservice.IfyouplantousetheacceleratorcardfromthecurrentdisplayconfigurationForreplacementandupgrade,youmustensurethatyoupurchaseacardthatcomplieswiththesystembusstandard.
Structure
Themaincomponentson thegraphicsacceleratoraretheGraphicsacceleratechipandrandommemory.Accessmemory(RAM), randomaccessmemorydigital-ad-analogconverter(RAMDAC), clocksynthesizer(ClockSynchesizer) andbasicinputoutputsystem(BIOS).
TherandomaccessmemoryRAMofthegraphicsacceleratorcanbecomposedofdynamicrandomaccessmemorychipDRAM,oritcanbecomposedofimagerandomaccessmemorychipwithbidirectionalaccessfunction,theformerischeap,Thelatterisexpensive,buttheimageaccessisfast.Thisisbecausethismemoryhasdualports,asintroducedintheimagememoryVRAM,ithastwoports,andimagedataflowsinfromoneport.VRAMcanflowoutfromtheotherendimmediately.Duringimageacceleration,thecolordataoftheimagepixelsthatflowedoutisimmediatelyconvertedintored,green,andblueintensityvoltagesthroughthedigital-to-analogconverter(RAMDAC)oftherandomaccessmemory.Thevalueissenttothemonitortoshowthecolor.
RAMDACissimilartothedigital-to-analogconverterintheattributecontrolleroftheVGAadapter.Italsocontainsacolorlook-uptable.ThroughtheimagecolordataoftheVRAM,thecorrespondingred,green,andbluedataissearchedfor.Outputthecolorvoltageofthethree-colorintensitytothedigital-to-analogconverter.
Theclocksynthesizerisusedtogeneratethesynchronizationsignalofthedisplayandtheclocksignalrelatedtothecontrol.
Thebasicinputandoutputsystem(BI0S)isthebasicinputandoutputsystemoftheimage,itsolidifiestheDOScallofmanyimagefunctions,justliketheBIOSinVGA.
Officium
Withtheimprovementofpixelresolutionandcolorresolution,itisrelativelyeasytoconstructavideosystem,andthecostisnothigh.Youonlyneedtoincreasetherefreshrate.Thestoragecapacityofthebufferissufficient.However,withtheincreaseinresolution,itmeansthatthecomputationalworkloadwillincreaseexponentiallyorevendozensoftimes,andtheworkloadofgraphicscontrolisalsoincreasingrapidly.InthePCvideosubsystem,bothcalculationandcontrolarecompletedbytheCPU.Astheamountofcalculationandcontrolincreases,itmeansthattheamountofinformationdisplayedonthescreenincreases,whichcanbeinferredthattheamountofinputandoutputinformationoftheentiresystemincreases,Resultinginoftenexceedingtherangeallowedbysystemresources.
Thewaytosolvethisproblemistoconstructaself-excitedmechanismintheformofagraphicsacceleratorinthevideosystem.Here,themainpurposeofthestandardvideosystemistorefreshthebasicmanagementmechanismofthebufferProvidedtothehardware,thebasicmanagementoftherefreshbufferismainlytomanageeachpixel,somespecialpixelsorpixelgroupsusedtocontrolthegraphicsunitgraphicscomponentssuchasgraphicsacceleratorsthatdisplaygraphicsblocks,andtodrawlinesegments,arcsandManagementoffunctionssuchashigh-levelgraphicsprimitivessuchasdisplaymodules.
Throughthededicatedgraphicsco-processor,theextendedfunctionscanbedirectlyrealizedonthehardware,andtheextendedfunctionscanalsoberealizedthroughthegraphicprogramminginterfacesupportedbythehardware.Generallyspeaking,theso-calledhardwaresupportreferstothestandardmicroprocessorsupport,anditprovidessupporttogetherwiththegraphicscontrolprogramresidingintheROM.Forsuchasystem,thehigh-levelprogramminginterfaceisaveryimportantinterface,veryusefulintheconstructionofgraphicsaccelerators.
ThegraphicsacceleratormainlyreceivestheCPU’sdescriptionofprimitives(usuallycommands,functions,andparametersdescribingattributes),andperformscoordinatesystemtransformation(transformstheworldcoordinatesystemintothedevicecoordinatesystem,mainlyfloatingPointcalculation),cropping,transformationratio,colorshading,windowopening,andhiddensurfaceremovaloperations,theoutputofwhichispixeloperation,photoelementoperation,andhigh-endgraphicsacceleratorsdirectlyoutputred,greenandbluecolorsignals.
Asagraphicssystemonaworkstation,inadditiontothegraphicsaccelerator,theremustalsobeagraphicslibrarysupportedbythegraphicsaccelerator,suchas:SUN'sGX,TurboGXplus,andSPARCstationZXgraphicsacceleratorssupportthecompany'sXGLgraphicslibrary,SGI’sIndygraphicsboard,RealityEnginZ,etc.allsupportthecompany’sIRISgraphicslibraryandOPENGL.
Theprincipleofacceleration
Thekeydeviceofthegraphicsacceleratoristhegraphicsaccelerationchip,whichsolidifiessomecommonlyusedsoftwareforbasicdrawingfunctionsandimageprocessingfunctions.Inthischip,whenthesedrawingfunctionsaretobeused,theCPUdoesnotneedtocalculateandcallsomedrawingfunctions,butisdirectlyexecutedbytheaccelerationchip,whichcangreatlyincreasethedrawingspeed.ForVGAorSVGA,theaboveprocessItisalsonecessarytotransferimagedatabackandforthbetweentheCPUandtheadapterthroughthebus,whichdelaysthetimeevenmore.Forthegraphicsaccelerator,theaboveprocessesareallperformedintheaccelerator,andnobusoperationisperformed.Thusspeedingupgraphicsgeneration.
Thegraphicsandimagefunctionssolidifiedinthegraphicsaccelerationchipvaryfrommanufacturertomanufacturer.Forexample,thegraphicsacceleratordesignedforWindowsissuitableforprocessinggraphicscomposedofregulargraphicssuchasmoldlinesandrectangles.BecauseintheWindowswindow,thegraphicsthatyouseearemostlycomposedoftheseregulargraphics,whenusedtoaccelerateirregulargraphics,suchasthree-dimensionalpaintingisnotapplicable.
GraphicsacceleratorsarefullycompatiblewithVGAandSVGA,andtheygenerallyuseVESAbusorPCIbus.
SincetheVRAMinthegraphicsacceleratorstorestheimagedatatobedisplayed,itrepresentsthelengthofapixeldataandthenumberofcolorsthatcanbedisplayed.Therefore,dependingontheVRAMcapacityandthedisplayresolution,theThenumberofcolorsdisplayedisalsodifferent.Table3.6showstheimageresolutionsupportedbythegraphicsaccelerator,thenumberofcolorsdisplayed,andtherequiredVRAMcapacity.
commoda
Thegraphicsacceleratorcanquicklycalculategraphicscalculations,suchasdrawingtriangles,andalsohavecalculationsforcommongraphicsandimageformats,suchasjpgdecompression,videostreamdecompression,etc.,withThecalculationofadvancedtextures,materials,andlightinggreatlyreducesthecomputationalburdenofthemainCPU,thereby"speedingup"thegraphicsandimages.
Theadvantagesofgraphicsacceleratorsareveryobvious:inadditiontotheobviousimprovementintheperformanceoftheentiregraphicssystem,italsosignificantlyreducesthepressureontheCPUduetothemanagementofmanygraphics,andsomehardwarehasreachedindependentoperationsituation.Withtheadvancedgraphicsinterface,itispossibletopreventprogrammersfromdirectlyoperatingonthevideohardware.Thiseffectivelyavoidscompatibilityissues.Inasense,thegraphicsacceleratoronlyeffectivelymeetstheneedsofthegraphicsprogramminginterface,andthegraphicsprogramminginterfaceshouldbeinstalledinthebiosfromthebeginning.