graphic system
Composition
Hardware:GraphicsI/Odevice
Graphicssoftware:generalprogrammingsoftwarepackage,specialapplicationsoftwarepackage
Generalcategory:Providesanextendedsetofgraphicsfunctionsthatcanbeusedinhigh-levelprogramminglanguages(suchasOpenGL)
Basicfunctions:primitivegeneration,attributesetting,selectionobservationandimplementationtransformation,etc.
Specialclass:Don’tcareaboutthegraphicsoperationprocess(forexample,CADsystem)
Systemcomposition
Computergraphicssystemconsistsofhardwareandsoftware.Thehardwareincludes:maincomputer,graphicsdisplayandI/Ointeractivetoolsandstoragedevices;softwareincludesoperatingsystems,high-levellanguages,graphicssoftwareandapplicationsoftware.
Themaindifferencebetweenmoderncomputergraphicssystemsandgeneralcomputersystemsisthattheyhavegraphicsinputandoutputdevices,aswellasnecessaryinteractivetools,andhavehigherrequirementsintermsofspeedandstoragecapacity.Inaddition,peoplearealsoanintegralpartofthissystem.
1.Basicfunctionsofgraphicssystem
1,calculationfunction
2,storagefunction
3.Inputfunction
4.Outputfunction
5.Dialoguefunction
Second,theclassificationofgraphicssystem
1.Graphicssystembasedonmainframes;
2.Graphicssystemsbasedonmedium-sizedcomputersorsuperminicomputers;
3.BasedonengineeringworkstationsGraphicssystem;
4.Graphicssystembasedonmicrocomputers;
Graphicshardwareequipment
First,displayequipment
Thedisplaydeviceisthepartthatultimatelyproducesthegraphicdisplayeffect.Varioustypesandtechnologiesofdisplaydeviceshaveappeared,butthecathoderaytube(CRT)isstillthedominantone.
1、CRT
(1)MonochromeCRT
Principle:Theelectricfieldisusedtogeneratehigh-speedfocusedelectronbeams,whicharedeflectedtodifferentpartsofthescreensurfacetoproduceVisiblegraphics.
Composition:electrongun,deflectionsystemandphosphorscreen.
Electrongun:Thecurrentpassesthroughthefilamenttogenerateheat,thatis,thecathodeisheatedtoemitanelectronbeam,acertainpositivevoltageisappliedtothefocusingelectrodetofocusitintoanelectronbeam,andthentheacceleratingelectrode(maybemultiple)Applyingapositivevoltagetoacceleratetheelectronbeam,sothatithasenoughenergytoshoottowardthephosphorscreen;thereisacontrolelectrodenearthecathode,afterapplyinganegativevoltage,thestrengthoftheelectronbeamcanbecontrolled,andtheelectronbeamcanalsobecutoff.
Deflectionsystem:Thedeflectioncanbecontrolledbyanelectrostaticfieldoramagneticfield(mostlyuseamagneticdeflectionsystem).
Whenusinganelectrostaticfield,twosetsofverticalandhorizontalflatplatesareplacedinsidetheneckofthecathoderaytube.
Themagneticdeflectionsystemisanexternaldeflectionsystem.Ithastwocoilswoundaroundthetubeneck.Whentheelectronbeampassesthroughthecoil,themagneticfieldofonecoildeflectstheelectronbeamhorizontally,andtheothermakesitverticaldeflection.
Themostimportantcharacteristicofthedeflectionsystemissensitivity,whichreflectsthemagnitudeofthedeflectionanglethatthedeflectionsignalcanproduce.
Fluorescentscreen:Thefluorescentscreeniscoatedwithfluorescentpowder,andtheelectronbeambombardsacertainpointofthefluorescentlayertoproducefluorescentbrightspots.Whentheelectronbeamleavesthispoint,itsbrightnessdecaysexponentiallywithtime.Afterglowtimereferstothetimerequiredforthelightvaluetodecayto1/10oftheinitialvalue.Theafterglowtimeofphosphorsusedingraphicsdevicesisgenerallytenstohundredsofmilliseconds.Inordertogetastable,non-flickeringpicture,itneedstobeconstantlyrefreshed.
ThequalityofthemonochromeCRTdisplayimagedependson:thesizeofthesinglespotdiameterinherentinthedeviceandthe"addressability".Addressabilitycanbeunderstoodasthenumberofsinglelightspotsthatcanbeusedperunitlength.Itisgenerallydesirablethatthediameterofthedotbelargerthanthedotpitch.ThemaximumnumberoflightspotsthataCRTcanrecognizeinthehorizontalorverticaldirectioniscalledtheresolution.
(2)ColorCRT
Therearetwobasicmethodsforgeneratingcolordisplay:Raypenetrationmethod,shadoworificemethod.
Raypenetratingmethod:Usedinrandomscandisplays,itiscoatedwithtwolayersofphosphor(redandgreen)onthescreen,thecolorofthedisplaydependsontheraypenetratingThedepthofthefluorescentlayer:low-speedelectronscanonlyexcitetheouterlayerofredpowder,andmedium-speedelectronscanexcitegreenpowderandredpowdertoproducetwoadditionalcolors:orangeandyellow,andhigh-speedelectronscanpenetratetheredlayertoexcitegreenpowder.Thisisaninexpensivemethod,butthegraphicsqualityislow.
Shadoworificemethod:Itiswidelyusedinrasterscanningsystems.ThiskindofCRTscreeniscoatedwithmanygroupsoftriangularphosphors,andeachgrouphasthreephosphordots.Whenacertaingroupofphosphorsareexcited,theyemitthreeprimarycolors.Threeelectrongunscorrespondingtoit.Thereisashadowholegridonthebackofthescreenwithmanysmallholescorrespondingtothetriplesonthescreen.Threebeamsofelectronsarefocusedintoagroupofrays,passingthroughthesmallholes,activatingatripleonthescreen,andcolordotsappear.Bycontrollingthestrengthoftheelectronbeam,theexcitedthreeprimarycolorscanbemixedintoawiderangeofcolorlevels.ThediameteroftheshadoworificeplatehasagreaterimpactontheresolutionoftheCRT.Thediameterissmallandthegraphicsqualityisgood,butthecostishighanddifficult.
(3)Direct-viewstoragetubeDVST
ThewritingelectrongunofthiskindofstoragetubeisnodifferentfromordinaryCRT,buttheelectronbeamisnotdirectlywrittenonthephosphorscreen,butonthestoragegridinfrontofthephosphorscreen.Thisisaverythinmetalmeshwithamediumonit.Thehigh-energyelectronbeamemittedbythewritingelectrongunbombardstheelectronsinthemediumonthegrid,andthebombardedplaceonthegridshowsapositivecharge,thatis,apositivechargetrackisformed.Thelow-energyelectronsemittedbythesecondelectrongun(readingelectrongun)flowtothecollector.Thecollectorspreadstheseelectronsevenlyandflowstothestoragegrid.Thepositivelychargedareaonthestoragegridattractselectronsandmakesthemglowbybombardingthephosphorscreen.OthersThepositiondoesnotpasselectrons,thatis,thememorygateplaysaroleinstoringpatternsandcontrollingthepassageofelectrons.Advantages:lowprice,noneedforhighrefresh;disadvantages:noselectivemodification.
2,othertypesofdisplaydevices
A,plasmapaneldisplay
Advantages:lightweight,Noneedtorefreshthecache;Disadvantages:lowresolutionandhighprice.
B.LiquidcrystaldisplaydeviceLCD
Advantages:lowprice,lightweight,smallsizeandlowconsumption;disadvantage:passivedisplay.
C,electroniclight-emittingdisplay
Advantages:highbrightness,fastonandoff;disadvantages:highprice,highpowerconsumption.
3,RandomScanDisplay
Thegraphicsdisplayedareprocessedbythecomputerintothedisplayinstructionsofthedisplay,thatis,displayfilesordisplayFilesanddisplayinstructionsaresenttothebuffermemoryofthedisplayviatheinterfacecircuit,andthefixedmemorystoresdisplayinstructionssuchascommonlyusedcharactersandnumbers.Thegraphicscontrollerfetchesthedisplayinstructionsinthebufferorfixedmemoryandexecutestheminsequence.Thedigitalinformationsuchasthebrightnessanddisplacementinthedisplaycommandistransformedintothephysicalquantitythatcontrolsthedeflectionandbrightnessoftheelectronbeambythewiregenerator,thatis,voltageandcurrent.Thenthetubeheadcontrolcircuitdeflectstheelectronbeamtothedesiredpositionwiththedesiredbrightness.Andcontinuetorefreshtomakeitstabledisplay.Sincethepositioninganddeflectionoftheelectronbeamarerandom,itiscalledrandomscanning.
Advantages:highresolution,obviouscontrast,richsoftware;disadvantages:expensive.
4,rasterscandisplay
TherasterscanCRTscreencanbedividedintomscanlines,eachlineisdividedintonsmalldots,eachdotiscalledapixel,andeachpixelcorrespondstoanumberofbitsintheframebuffermemory.Onlyonebitisneededforablack-and-whiteimage;ifeachpixelusesibitstorepresentitsgraylevel,thenCanproduce2igrayscaleorcolor.Thatis,intheframebufferoftherasterscandisplay,whatisstoredisnotthedisplaycommand,butthebrightnessorcolorinformationofthecorrespondingpixel.Thisinformationiscalledabitmap.
Thecomputerconvertsthegraphicsandimagestobedisplayedintobitmaps,andsendsthemtotheframebufferviatheinterfacecircuit.Thegraphicscontrollercontrolstheelectronbeamtofollowafixedscanlineandscanningsequenceandreaditfromtheframebuffer.Thepixelvaluescanstheentirescreen.Afterthescaniscompleted,thedisplaycontrollerappliestothecomputerforinterruption,sothatthecomputercanusethetimeoftheframeretracetomodifythecontentintheframebuffer,soastomodifythepicture.
Togetastablepicture,itneedstoberefreshed;high-speedandlarge-capacitymemoryisrequired;scanningisdividedintointerlacedandprogressive.
Theadvantagesoftherasterscandisplay:lineandsurfacegraphics,thepictureisreal;thepriceislow;thedisadvantages:theconversionistime-consumingandthesoftwareiscomplicated.
5,displayprocessor(DPU)
Inthegraphicssystem,inordertoreducetheBurden,generallyinadditiontotheCPU,thereisadedicateddisplayprocessor(DPU)tointeractwiththeCPUandcontroltheoperationofthedisplaydevice.
(1)DPUofrandomscanningsystem
TheDPUofrandomscanningsystemisverydifferent,andthecomplexityisdifferent.
ThiskindofDPUcanbeequippedwithacacheornot(withthehelpofmainmemory).Whenthereisnocache,thehostCPUrunstheprogramtoformthedisplayfileoftheDPU,andthehostCPUstartsthedisplayfile.ThestartingaddressissenttotheinstructioncounteroftheDPU.TheDPUreadsthedisplayinstructionsfromthememoryinturnaccordingtothisstartingaddress,andsendsthemtotheinstructionregister,thendecodestheopcode,andexecutestheinstructionswiththeparticipationofthecontrollogic.ThiskindofDPUisrelativelysimple.Buttheonewithcacheismorecomplicatedandpowerful.
(2)DPUofrasterscanningsystem
Inasimplerasterscanningsystem,theCPUfirstcalculatestheframebufferaddresscorrespondingtothecoordinatesofeachpixelpoint,andassignsthebrightnessOrthecolorvalue,butthefunctionisweakandtheefficiencyislow.TherasterscanningsystemwithindependentDPUcanovercometheabove-mentionedshortcomings.
ThisDPUisspecificallyusedtoscanandconvertoutputpixelsintopixelbitmaps,andperformrasteroperationssuchaspixelorpixelblockshifting,copying,andmodification.TherasterscansystemwithindependentDPUhasthreememories:systemmemory,displayprocessormemory,andframebuffermemory.
ThesimpleDPUonlyperformssomepossiblegraphics-relatedoperations;whilethestrongeronescanachieveinteractiveoperationssuchascropping,windowviewtransformation,andpick-relatedlogicandfeedback.SomeDPUsalsohaveadisplaytablememorytostoredisplayinstructionsinsegments,andoperationssuchastransformationandredrawingcanbeperformedthroughthesesegments.
(3)ThedevelopmentstageofDPU
Thefirstgenerationofsingle-chipgraphicsprocessors:Hitachi’sHD-63484in1984;TexasCompany’sTMS34010in1986;IntelThecompany's82786.
Thesecond-generationsingle-chipgraphicsprocessor:the72120ofNEC;theTMS34020ofTexasin1988;theGDPofHitachi.
Multi-chipgraphicsprocessor:AMD’s9560four-pixeldatastreammanager;NationalSemiconductor’sAdvancedGraphicsChipset(ADCS).
General-purposemicroprocessorsareusedasgraphicsprocessors:ForlandiVARS.
Graphicsmachinewithpipelinemulti-processorstructure:Eachhigh-levelgraphiccommandneedstogothroughaprocessofstepwisegeometrictransformation,andfinallyformanoutputintheformofabitmap.Atypicalpipelinestructureincludesthreeindependentprocessors:adisplaytableorcommandprocessor,ageometryprocessor,andadisplaycontrollerordisplayprocessor,whichisactuallymuchthinnerthanthree.Itsperformanceismuchhigherthanasingle-chipgraphicsprocessor,TexasInstruments'88XX.
Illustrationsystemofarraystructure:T800ofImmos.
Second,hardcopyequipment
1,dotmatrixprinter
2,penplotter
3,electrostaticplotter
4,laserprinter
5,inkjetplotter
6,thermalconversionprinter
7,Camera
3.Inputdevice
Thegraphicinputdevicecanconverttheuser’sgraphicdataandvariouscommandsintoelectricalsignalsandtransmitthemTothecomputer.Fromalogicalpointofview,itcanbedividedintosixtypesoffunctions,namelypositioning,strokes,sendingvalues,selection,pickingandcharacterstrings,alsoknownassixtypesoflogicaldevices.Theso-calledlogicaldevicereferstoadevicedefinedbylogicalfunction,notaspecificphysicaldevice.Theactualphysicaldeviceisoftenacombinationofcertainlogicaldevices.
1.Locator:usedtoindicateaposition,theinputisx,y.Commonlocatorsare:coordinatedigitizer,graphicstablet,mouse,trackball,joystick,touchcontrolpanel,acousticinputpanel,etc.
2.Picker:usedtopickupashape,groupofpicturesorpixelsonthedisplayscreen.Typicalpick-updevicesincludelightpensandgraphicstablets.
3.Setter:Itisaphysicaldevicethatprovidesascalarvalue.
4.Keyboard:usedtoinputcharactersorstrings,etc.
5.Buttons:usedtoselectfromasetofactionsorfunctions,suchasaprogrammedfunctionkeyboard.
6.Otherequipment:suchasvoicerecognizer,etc.
Graphicssoftwaresystem
First,thecompositionofgraphicssoftware
ThegraphicssoftwaresystemshouldhaveagoodstructureandbereasonableHierarchicalmodularstructureforeasydesign,maintenanceanddebugging.
1.Zero-levelgraphicssoftware:itisthelowestlevelsoftware,whichmainlysolvesthecommunicationandinterfaceproblemsbetweenthegraphicsdeviceandthehost.Itisalsocalledthedevicedriver.Itissomeofthemostbasicinputandoutputsubroutines.Theprogramrequireshighquality,itissystem-oriented,notuser-oriented.
2.First-levelgraphicssoftware:alsoknownasbasicsubroutines,includingprogrammodulesthatgeneratebasicgraphicelementsandmanageequipment,whicharebothsystem-orientedanduser-oriented.
3.Second-levelgraphicssoftware:alsocalledfunctionalsubroutines.Itiscompiledonthebasisoffirst-levelgraphicssoftware.Itsmaintaskistoestablishgraphicsdatastructure,define,modifyandoutputgraphics;andestablishvariousTheconnectionbetweengraphicsdevicesmusthaveastronginteractivefunction,whichisuser-oriented.(Theabovethreelevelsareusuallyreferredtoassupportingsoftware)
4.Three-levelgraphicssoftware:graphicssoftwaretosolveacertainapplicationproblem.Itisapartoftheentireapplicationsoftware.Itisusuallywrittenbytheuserorwiththedesigner.Writetogether.
Second,thebasicgraphicssoftware
1.Thecontentofthebasicgraphicssoftware
Thebasicgraphicssoftwareisthesupportingsoftwareofthegraphicssystem.Itsfunctionscanvaryaccordingtoneeds,butitsbasiccontentshouldgenerallyinclude:
(1)Systemmanagementprogram;
(2)DefineandoutputbasicpixelsandcompositesPixelgraphicsprogram;
(3)Graphicstransformation,includinggeometrictransformation,windowing,cropping,etc.;
(4)Real-timeinputprocessingprogram;
(5)Interactiveprocessingprogram;
2.Methodofestablishingbasicgraphicssoftware
(1)Addgraphicspackageonthebasisofhigh-levellanguage;
(2)Modifythehigh-levellanguage;
(3)Specialhigh-levelgraphicslanguage;
3.Theconnectionbetweengraphicssoftwareandothersoftwareresources
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1.Thechoiceofhigh-levellanguage
Thegraphicssoftwarepackageisbasedonacertainhigh-levellanguage.Thefollowingfactorsshouldbeconsideredwhenchoosingwhichhigh-levellanguage:
Choosealanguagethatismorecommoninthefieldofengineeringtechnology;
High-levellanguagewithmodularstructure;
Languagewithrichersupportingsoftware;
RichdatatypesFlexiblelanguage;
LanguagewithstrongerI/Ofunction;
Languagewithbettertargetprogramquality;
2,OSselection
ThestrengthoftheOSsystemgreatlyaffectsthefunctionsofothersystemsoftware.Inaddition,thegraphicssystemhasmanyI/Odevices.Tomanagethesedevices,youcandevelopgraphicsOS,modifyOS,andmanagegraphicssoftwarepackagesthemselves.
Four.Practicalgraphicssoftwarepackage
1.IBM-PCbasicassemblyinstructiondriver
(1)Setscreenstatus;
(2)Drawapoint;
(3)Setthescreentocharactermode;
2,MicrosoftC/C++runtimelibraryroutines
p>(1)Configurationmethodandenvironment;
(2)Setcoordinates;
(3)Setlow-levelgraphicspalette;
(4)Setattributevalues;
(5)Generategraphicsandtextoutput;
(6)Transferimagesanddisplayfonts;
GraphicssoftwareStandards
Thegraphicsstandardsthathavebeenformulatedareallinterfacestandards.Thesestandardsaimtostandardizetheinterfacebetweenthetwopartsofthegraphicssystem.Theyaredividedintotwocategories:
Datainterfacestandards:Usedtodeterminethestandardofdatatransferandcommunicationbetweentheinterfacesofthesystem;
Subprograminterfacestandard:stipulatesthestandardofthefunctionandformatoftheapplicationcallingthesubprogram;
Thelocationisdifferent,theserviceprovidedisalsodifferent.
(1)BasicgraphicsexchangespecificationIGES
ItbecameanANSIstandardin1981.Itsfunctionistoexchangedatabetweendifferentgraphicssystems.Itsbasicunitisanentity.Theentitiesaredividedintothreecategories:geometricentities,descriptionentitiesandstructuralentities.ThefileformatiscomposedofasequentialfilewithASCIIcodeandarecordlengthof80characters.Thefileisdividedintofivesectionsandanerrorhandlingmechanismisprovided.
(2)GraphicsCoreSystemGKS
GKSProvidesafunctionalinterfacebetweenapplicationprogramsandgraphicsinputandoutputdevices.Itisasubroutineinterfacestandardandisthecoreofalanguage-independentgraphicssystem.
GKSisthecoreofthesystem.Thegraphicsfunctionitprovidesisindependentofspecialgraphicsequipment.Itcancallinput,output,inputandoutput,independentimagesegmentstorage,metafileoutput,metafileinput,etc.Sixkindsofabstractphysicaldevices(graphicworkstations),whichallowoutputpixelstobetransformedandtransmittedondifferentworkstations;itincludesbasicpixelssuchaslineelements,pointelements,characterelements,andrasterelements,whichworkandcombineinthemannerofsegments,Usemetafilestotransfergraphicsbetweengraphicssystems.GKSisatwo-dimensionalgraphicsstandard,andGKS-3Disathree-dimensionalgraphicsstandard.
(3)Programmer-levelhierarchicalgraphicssystemPHIGS
ItisANSIpromulgatedin1986toprovideapplicationprogrammerswithasubprograminterfacestandardforcontrollinggraphicsdevices.Itcanbedividedintonineprogrammodulestobeimplementedseparately.Eachmoduleisindependentandonlyconnectstoothermodulesthroughacommondatastructure..Allgraphicdataisorganizedinunitscalledstructures,andthestructuresareconnectedthroughhierarchicalcalls.Thestructurecanincludegraphicelements,modeltransformationmatrixelements,observationselectionelements,applicationdataelements,andstructurecallelements.Theapplicationcancreateastructurebycallinganon-existingstructure,openinganexistingstructure,logginganon-existingstructuretotheworkstation,andquotingastructurenamewhenchangingthestructureidentifier.Andprovidesaneffectivemeansofeditingthestructure.ComparedwithGKS,itsdifferenceisreflectedin:datastructure,modifiable,attributestorage,outputpipeline,etc.
(4)ComputergraphicsdeviceinterfaceCGI
ItisadeviceinterfacedraftproposedbyISOTC97.ItisconsistentwiththeVDIstandardpublishedbyANSIin1985.Itprovidesastandardforvisualgraphicsdevicedriversandisaprograminterfacestandard.
(5)ComputerGraphicsMetafileCGM
ItisastandardproposedbyANSIin1986andbecameanISOstandardin1987.Itisasetofdevice-independentsemanticandlexicalgraphicfileformatsthatproviderandomaccess,transmission,andconcisedefinitionofimages.Versatilityisitskeyattribute,itisakindofstaticgraphicsgeneratingmetafile.Thestandardconsistsoftwoparts,oneisthefunctionalspecification,whichdescribesthecorrespondingfileformatwithabstractlexicon;theotheristhedescriptionofthethreestandardcodingformsofCGM,namelycharacter,binaryandcleartextcoding.
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