資料詳解第4章和

4.1TheMFCDeviceContext4.1.1DrawingLinesand4.1.3TheMap4.2GDI4.2.2StockGDI4.3Drawing4.3.1Text4.3.2TheMFCDeviceContextWhenaWindowsprogramdrawstoascreen,aprinter,oranyotheroutputdevice,itdoesn'toutputpixelsdirectlytothedevice.Instead,itdrawstoalogical"disysurface"representedbyadevicecontext(DC).TheMFCDeviceContextAdevicecontextisadatastructuredeepinsideWindowsthatcontainsfieldsdescribingeverythingtheGDIneedstoknowaboutthedisysurface,ludingthephysicaldevicewithwhichitisassociatedandassortedstateinformation.TheMFCDeviceContextBeforeitdrawsanythingonthescreen,aWindowsprogramacquiresadevicecontexthandlefromtheItthenpassesthathandlebacktotheGDIeachtimeitcallsaGDIoutputfunction.TheMFCDeviceContextDevicecontextsyahugeroleinmakingtheGDIdevice-tbecause,givenahandletoadevicecontext,thesameGDIfunctionscanbeusedtodrawtoadiverseassortmentofoutputdevices.TheMFCDeviceContextWhenyouprogramWindowswithMFC,thedevicecontexthasevengreatersignificance.Inadditiontoservingasthekeythatunlocksthedoortooutputdevices,adevicecontextobjectencapsulatestheGDIfunctionsthatprogramsusetogenerateoutput.TheMFCDeviceContextInMFC,youdon'tgrabahandletoadevicecontextandcallGDIoutputfunctions,atleastnotdirectly;instead,youcreateadevicecontextobjectandcallitsmemberfunctionstodoyourTheMFCDeviceContextMFC'sCDCclasswrapsaWindowsdevicecontextandtheGDIfunctionsthatrequireadevicecontexthandleintooneconvenientpackage,andCDC-derivedclassessuchasCPaintDCand DCrepresentthedifferenttypesofdevicecontextsthatWindowsapplicationsuse.TheMFCDeviceContextOnewaytogetadevicecontextinanMFCapplicationistocallCWnd::GetDC,whichreturnsapointertoaCDCobjectrepresentingaWindowsdevicecontext.AdevicecontextpoincquiredwithCWnd::GetDCshouldbereleasedwithCWnd::ReleaseDCwhendrawingiscompleted.ThefollowingcodegetsaCDCpointerfromGetDC,doessomedrawing,andcallsReleaseDCtoreleasethedevicecontext:CDC*pDC=GetDC//DosomedrawingReleaseDC(pDC);TheMFCDeviceContextCDC*GetDC();ReturnIdentifiesthedevicecontextfortheareaifsuccessful;otherwise,thereturnvalueisNULL.Thepointermaybetemporaryandshouldnotbestoredforlateruse.TheMFCDeviceContextintReleaseDC(CDC*pDCReturnNonzeroifsuccessful;otherwisepDC:IdentifiesthedevicecontexttobeReleasesadevicecontext, ingitforusebyotherapplications.TheeffectoftheReleaseDCmemberfunctiondependsonthedevice-contextTheMFCDeviceContextIfthesamecodeweretoappearinanOnPainthandler,youwoulduseCWnd::BeginPaintandCWnd::EndPaintinceofGetDCandReleaseDCtoensureproperhandlingoftheWM_PAINTmessage:CDC*pDC=BeginPaint//DosomeEndPaintTheMFCDeviceContextReturnIdentifiesthedevicecontextforCWnd.ThepointermaybetemporaryandshouldnotbestoredbeyondthescopeofEndPaint.lpPaint:PointstothePAINTSTRUCTstructurethatistoreceivepaintinginformation.PreparesCWndforpaintingandfillsaPAINTSTRUCTdatawithinformationabouttheTheMFCDeviceContextvoidEndPaint(LPPAINTSTRUCTlpPaintlpPaint:PointstoaPAINTSTRUCTstructurethatcontainsthepaintinginformationretrievedbytheBeginPaintmemberfunction.Marksofpaintinginthegivenwindow.PaintmemberfunctionisrequiredforeachcalltotheBeginPaintmemberfunction,butonlyafterpaintingiscomplete.IfthecaretwashiddenbytheBeginPaintmemberfunction,EndPaintrestoresthecarettothescreen.4.1TheMFCDeviceContextCC4.1TheMFCDeviceContextSpecial-PurposeDeviceContextClassFordrawinginawindow's area(OnPainthandlersonly) Fordrawinginawindow's area(anywherebutOnPaint)Fordrawinganywhereinawindow, ludingthe FordrawingtoaGDI4.1TheMFCDeviceContextTheC DCclassisderivedfromCDCandtakescareofcallingtheWindowsfunctionsGetDCatconstructiontimeandReleaseDCatdestructionAwindow'sareaexcludestheborder,thecaptionbar,andthebar.IfyoucreateaCDCobject,youhaveadevicecontextthatismappedonlytothisarea—youcan'tdrawoutsideit.Thepoint(0,0)usuallyreferstotheupper-leftcornerofthearea.4.1TheMFCDeviceContextTheCWindowDCclassisderivedfromCDC.ItcallstheWindowsfunctionsGetWindowDCatconstructiontimeandReleaseDCatdestructionIfyouconstructanobjectofclassCWindowDC,thepoint(0,0)isattheupper-leftcornerofthe areaoftheWiththiswhole-windowdevicecontext,youcandrawinthewindow'sborder,inthecaptionarea,andso4.1TheMFCDeviceContextTheCPaintDCclassisadevice-contextclassderivedfromCDC.ItperformsaCWnd::BeginPaintatconstructiontimeandCWnd::EndPaintatdestructiontime.MFC'sCPaintDCclassletsyoupaintinawindow'sareainresponsetoWM_PAINTmessages.YoushoulduseitonlyinOnPainthandlersandneveranywhereelse.4.1TheMFCDeviceContextCDC*pDC=GetDC();CDC*pDC=Createafullscreendevice-contextCDC*pDC=4.1TheMFCDeviceContextvirtualintSaveDC();ReturnAnintegeridentifyingthesaveddevicecontext.Itis0ifanerroroccurs.ThisreturnvaluecanbeusedtorestorethedevicecontextbycallingSavesthecurrentstateofthedevicecontextbycopyingstateinformation(suchasclipregion,selectedobjects,andmapmode)toacontextstackmaintainedbyWindows.ThesaveddevicecontextcanlaterberestoredbyusingRestoreDC.4.1TheMFCDeviceContextvirtualBOOLRestoreDC(intnSavedDCReturnNonzeroifthespecifiedcontextwasrestored;otherwisenSavedDC:Specifiesthedevicecontexttoberestored.ItcanbeavaluereturnedbyapreviousSaveDCfunctioncall.IfnSavedDCis1,themostrecentlysaveddevicecontextisrestored.RestoresthedevicecontexttothepreviousstateidentifiedbynSavedDC.RestoreDCrestoresthedevicecontextbypopstateinformationoffastackcreatedbyearliercallstotheSaveDCmember4.1TheMFCDeviceContexttypedefstruct{LONGLONG}CPoint::CPoint(intinitX,intinitY);CPoint::CPoint(POINTinitP);4.1TheMFCDeviceContexttypedefstruct{intx;intCSize::CSize(intinitCX,intinitCY);CSize::CSize(SIZEinitSize);4.1TheMFCDeviceContexttypedefstruct{LONGleft;//x-coordinateoftheupper-leftcorneroftherectangleLONGtop;//y-coordinateoftheupper-leftcorneroftherectangleLONGright;//x-coordinateofthelower-rightcorneroftherectangleLONGbottom;//y-coordinateofthelower-rightcorneroftherectangleCRect::CRect(intl,intt,intr,intb);CRect::CRect(constRECT&srcRect);CRect::CRect(LPCRECTlpSrcRect);CRect::CRect(POINTpoint,SIZEsize);CRect::CRect(POINTtopLeft,POINTSomeCDCFunctionsforDrawingLinesandSetsthecurrentpositioninpreparationfor Drawsalinefromthecurrentpositiontoapositionandmovesthecurrentpositionto theline.Connectsasetofpointswithline Connectsasetofpointswithlinesegmentsbeginningwiththecurrentpositionandmovesthecurrentpositionto ofthepolyline.DrawsanDrawsanarcandmovesthecurrentpositiontoendoftheCPointMoveTo(intx,inty);CPointMoveTo(POINTpoint);ReturnThex-andy-coordinatesofthepreviouspositionasaCPointx:Specifiesthelogicalx-coordinateofthenewposition.y:Specifiesthelogicaly-coordinateofthenewpoint:Specifiesthenewposition.YoucanpasseitheraPOINTstructureoraCPointobjectforthisparameter.Movesthecurrentpositiontothepointspecifiedbyxandy(orbyExample1:for(int{CPoint} BOOLL o(intx,inty);BOOLL o(POINTpoint);ReturnNonzeroifthelineisdrawn;otherwisex:Specifiesthelogicalx-coordinateof pointfortheline.y:Specifiesthelogicaly-coordinateof pointfortheline.point:Specifies pointfortheline.YoucanpasseitheraPOINTstructureoraCPointobjectforthisparameter.Drawsalinefromthecurrentpositionupto,butnot luding,thepointspecifiedbyxandy(orpoint).Thelineisdrawnwiththeselectedpen.Thecurrentpositionissettox,yortoExample2:L CPenpen;pen.CreatePen(PS_SOLID,2,RGB(255,0,0))CPen*pOldPen=pDC- opDC->MoveTo oBOOLPolyline(LPPOINTlpPoints,intnCountReturnNonzeroifthefunctionissuccessful;otherwiselpPoints:PointstoanarrayofPOINTstructuresorCPointobjectstobenCount:Specifiesthenumberofpointsinthearray.Thisvaluemustbeatleast2.DrawsasetoflinesegmentsconnectingthepointsspecifiedbyExample3:CPenCPen*pOldPen=pDC-CPointp[5]={CPoint(50,50),CPoint(100,50),CPoint(100,100),pDC->Polyline(p,5Example4: CPenCPen*pOldPen=pDC-pDC->MoveTo(0,0CPointp[5]={CPoint(50,50),CPoint(300,50),CPoint(300,300), o(p,5BOOLArc(intx1,inty1,intx2,inty2,intx3,inty3,intx4,inty4BOOLArc(LPCRECTlpRect,POINTptStart,POINTptEndlpRect:Specifiestheboundingrectangle(inlogicalunits).YoucanpasseitheranLPRECToraCRectobjectforthisparameter.ptStart:Specifiesthex-andy-coordinatesofthepointthatdefinesthearcsstartingpoint(inlogicalunits).Thispointdoesnothavetolieexactlyonthearc.YoucanpasseitheraPOINTstructureoraCPointobjectforthisptEnd:Specifiesthex-andy-coordinatesofthepointthatdefinesthearcsendingpoint(inlogicalunits).Thispointdoesnothavetolieexactlyonthearc.YoucanpasseitheraPOINTstructureoraCPointobjectforthisparameter.Example5:CPenCPen*pOldPen=pDC-CPointp[5]={CPoint(50,50),CPoint(300,50),CPoint(300,300),pDC->Polyline(p,5CDCFunctionsforDrawingClosedDrawsaclosedfigureboundedbytheintersectionofanellipseandalineDrawsacircleoranDrawsapie-shapedConnectsasetofpointstoformaDrawsarectanglewithsquareDrawsarectanglewithroundedBOOLRectangle(intx1,inty1,intx2,inty2);BOOLRectangle(LPCRECTlpRect);x1:Specifiesthex-coordinateoftheupper-leftcorneroftherectangle(inlogicalunits).y1:Specifiesthey-coordinateoftheupper-leftcorneroftherectangle(inlogicalunits).x2:Specifiesthex-coordinateofthelower-rightcorneroftherectangle(inlogicalunits).y2:Specifiesthey-coordinateofthelower-rightcorneroftherectangle(inlogicalunits).lpRect:Specifiestherectangleinlogicalunits.YoucanpasseitheraCRectobjectorapointertoaRECTstructureforthisDrawsarectangleusingthecurrentpen.Theinterioroftherectangleisfilledusingthecurrentbrush.CBrushbs;CBrush*pOldBrush=pDC-CRectBOOLEllipse(intx1,inty1,intx2,inty2);BOOLEllipse(LPCRECTlpRect);x1:Specifiesthelogicalx-coordinateoftheupper-leftcorneroftheellipsesboundingrectangle.y1:Specifiesthelogicaly-coordinateoftheupper-leftcorneroftheellipsesboundingrectangle.x2:Specifiesthelogicalx-coordinateofthelower-rightcorneroftheellipsesboundingrectangle.y2:Specifiesthelogicaly-coordinateofthelower-rightcorneroftheellipsesboundingrectangle.lpRect:Specifiestheellipsesboundingrectangle.Youc sopassaCRectobjectforthisparameter.Example7:CBrushbs;CBrush*pOldBrush=pDC-CRectrect(0,0,100,100);//CRectBOOLPolygon(LPPOINTlpPoints,intnCountlpPoints:Pointstoanarrayofpointsthatspecifiestheverticesofthepolygon.EachpointinthearrayisaPOINTstructureoraCPointnCount:SpecifiesthenumberofverticesintheDrawsapolygonconsistingoftwoormorepoints(vertices)connectedbylines,usingthecurrentpen.Thesystemclosesthepolygonautomatically,ifnecessary,bydrawingalinefromthelastvertextothefirst.Example8:CPenCPen*pOldPen=pDC-CPointpoly[4];themapmodeistheattributeofthedevicecontextthat ernshowlogicalcoordinatesaretranslatedintodevicecoordinates.LogicalcoordinatesarethecoordinatesyoupasstoCDCoutputfunctions.Devicecoordinatesarethecorrespondingpixelpositionswithinawindow.MapLogicalAxes1x:right,0.1x:right,y:0.01x:right,y:0.01x:right,y:0.001x:right,y:1/1440in.(0.0007x:right,y:dc.Rectangle(0,0,200,100);drawsa200-pixelby100-pixelrectangleintheMM_TEXTmapmode.ThesamestatementproducesnooutputintheMM_LOENGLISHmapmodebecausepositiveycoordinateslieoutsidethevisiblepartofthewindow.TheMM_ISOTROPICandmapmodesdifferfromtheothermapmodesinoneimportantrespect:It'syou,notWindows,whodetermineshowlogicalcoordinatesareconvertedintodevicecoordinates.ThemostcommonusefortheMM_ISOTROPICandMM_ANISOTROPICmapmodesisfordrawingoutputthatautomaticallyscalestomatchthewindowsize.CRect AWindowsGDIobjecttypeisrepresentedbyanMFClibraryclass.CGdiObjectisthe classfortheGDIobjectclasses.AWindowsGDIobjectisrepresentedbyaC++objectofaclassderivedfromCGdiObject.Here'salistoftheGDIderivedclasses:CBitmap—Abitmapisanarrayofbitsinwhichoneormorebitscorrespondtoeachdisypixel.Youcanusebitmapstorepresentimages,andyoucanusethemtocreatebrushes.CBrush—Abrushdefinesabitmappedpatternofpixelsthatisusedtofillareaswithcolor.CFont—Afontisacompletecollectionofcharactersofaparticulartypefaceandaparticularsize.Fontsaregenerallystoredondiskasresources,andsomeareCPalette—Apaletteisacolormapinterfacethatallowsanapplicationtotakefulladvantageofthecolorcapabilityofanoutputdevicewithoutinterferingwithotherapplications.CPen—Apenisatoolfordrawinglinesandshapeborders.Youcanspecifyapen'scolorandthicknessandwhetheritdrawssolid,dotted,ordashedlines.CRgn—Aregionisanareawhoseshapeisapolygon,anellipse,oracombinationofpolygonsandellipses.Youcanuseregionsforfilling,clip,andmousehit-YouneverconstructanobjectofclassCGdiObject;instead,youconstructobjectsofthederivedclasses.ConstructorsforsomeGDIderivedclasses,suchasCPenandCBrush,allowyoutospecifyenoughinformationtocreatetheobjectinonestep.Others,suchasCFontandCRgn,requireasecondcreationstep.Fortheseclasses,youconstructtheC++objectwiththedefaultconstructorandthenyoucallacreatefunctionsuchastheCreateFontorCreatePolygonRgnfunction.Pens,brushes,andotherobjectscreatedfromCGdiObject-derivedclassesareresourcesthatconsumespaceinmemory,soit'simportanttodeletethemwhenyounolongerneedIfyoucreateaCPen,CBrush,CFont,orotherCGdiObjectonthestack,theassociatedGDIobjectisautomaticallydeletedwhenCGdiObjectgoesoutofscope.IfyoucreateaCGdiObjectontheheapwithnew,besuretodeleteitatsomepointsothatitsdestructorwillbecalled.TheGDIobje sociatedwithaCGdiObjectcanbeexplicitlydeletedbycallingCGdiObject::DeleteObject.Youneverneedtodeletestockobjects,eveniftheyare"created"withIt'simportanttodeletetheGDIobjectsyoucreate,butit'sequallyimportanttoneverdeleteaGDIobjectwhileit'sselectedintoadevicecontext.Codethatattemptstopaintwithadeletedobjectisbuggycode.Theonlyreasonitdoesn'tcrashisthattheWindowsGDIissprinkledwitherror-checkingcodetopreventsuchcrashesfrom{CPennewPen(PS_DASHDOTDOT,2,(COLORREF)0);//black//2pixelsCPen*pOldPen=pDC- o(110, //newPenis}//newPenautomaticallydestroyedonCPen:TheCPenclassencapsulatesaWindowsgraphicsdeviceinterface(GDI)pen.CPen(intnPenStyle,intnWidth,COLORREFcrColor);nPenStyle:Specifiesthepenstyle.nWidth:Specifiesthewidthofthepen.crColor:ContainsanRGBcolorfortheTheparameternPenStylecanbeanyoneofthefollowing Createsasolid Createsadashedpen.Validonlywhenpenwidthis1orless,indevice Createsadottedpen.Validonlywhenpenwidthis1orless,indevice Createsapenwithalternatingdashesanddots.Validonlwhenthepenwidthis1orless,indeviceunits. Createsapenwithalternatingdashesanddoubledots.Validonlywhenthepenwidthis1orless,indevice CreatesanullBOOLCreatePen(intnPenStyle,intnWidth,COLORREFcrColor);nPenStyle:Specifiesthepenstyle.nWidth:Specifiesthewidthofthepen.crColor:ContainsanRGBcolorfortheCBrush:TheCBrushclassencapsulatesthefunctionalityofaWindowsgraphicsdeviceinterface(GDI)brush,whichisabitmapthatisusedtofilltheinteriorofclosedshapes.CBrush(COLORREFcrColorCBrush(intnIndex,COLORREFcrColorCBrush(CBitmap*pBitmapcrColor:SpecifiestheforegroundcolorofthebrushasanRGBcolor.Ifthebrushishatched,thisparameterspecifiesthecolorofthenIndex:SpecifiesthehatchstyleofthepBitmap:PointstoaCBitmapobjectthatspecifiesabitmapwithwhichthebrushpaints.TheparameternIndexcanbeanyoneofthefollowing Downwardhatch(lefttoright)at45degree Horizontalandverticalcrosshatch Crosshatchat45degrees Upwardhatch(lefttoright)at45degrees Horizontalhatch VerticalCBrushbrush;CBitmapbit;CBrush*poldbrush=pDC->SelectObject(&brush);CommonlyUsedStockPenthatdrawsBlackpenthatdrawssolidlines1pixelWhitepenthatdrawssolidlines1pixelBrushthatdrawsBrushthatdrawsnothing(sameasBlackDarkgrayMediumgrayWhiteFixed-pitchANSIVariable-pitchsystemWindowscontainsanumberofstockGDIobjectsthatyoucanuse.BecausetheseobjectsarepartofWindows,youdon'thavetoworryaboutdeletingthem.(Windowsignoresrequeststodeletestockobjects.)TheMFClibraryfunctionCDC::SelectStockObjectselectsastockobjectintothedevicecontextandreturnsapointertothepreviouslyselectedobject,whichitStockobjectsarehandywhenyouwanttodeselectyourownnonstockGDIobjectpriortoitsdestruction.Youcanuseastockobje ternativetothe"old"objectyouused.CGdiObject*pOld=pDC->SelectStockObject(DKGRAY_BRUSH);4.3DrawingCommonlyUsedCDCTextDrawstextinaformattingOutputsalineoftextatthecurrentorspecifiedComputesthewidthofastringinthecurrentReturnsfontmetrics(characterheight,averagecharacterwidth,andsoon)forthecurrentfontSetsalignmentparametersforTextOutandotheroutputfunctionsSpecifiestheaddedwidththatisneededtojustifyastringoftextSetsthedevicecontext'stextoutputSetsthedevicecontext'sbackgroundCDC::virtualBOOLTextOut(intx,inty,LPCTSTRlpszString,intnCount);BOOLTextOut(intx,inty,constCString&str);x:Specifiesthelogicalx-coordinateofthestartingpointofthetext.y:Specifiesthelogicaly-coordinateofthestartingpointofthetext.lpszString:Pointstothecharacterstringtobedrawn.nCount:Specifiesthenumberofbytesinthestr:ACStringobjectthatcontainsthecharacterstobeWritesacharacterstringatthespecifiedlocationusingthecurrentlyselectedfont.CDC::virtualCSizeTabbedTextOut(intx,inty,LPCTSTRintnCount, LPINTlpnTabStopPositions,in abOrigin);CSizeTabbedTextOut(intx,inty,constCString&str,in LPINTlpnTabStopPositions, abOriginnTabPositions:Specifiesthenumberofvaluesinthearrayoftab-stoppositions.lpnTabStopPositions:Pointstoanarraycontainingthetab-stoppositions(inlogicalunits).Thetabstopsmustbesortedin reasingorder;thesmallestx-valueshouldbethefirstiteminthearray.nTabOrigin:Specifiesthex-coordinateofthestartingpositionfromwhichtabsareexpanded(inlogicalunits).Callthismemberfunctiontowriteacharacterstringatthespecifiedlocation,expandintabstothevaluesspecifiedinthearrayoftab-stoppositions.virtualintDrawText(LPCTSTRlpszString,intnCount,LPRECTUINTnFormatintDrawText(constCString&str,LPRECTlpRect,UINTnFormatlpszString:Pointstothestringtobedrawn.SpecifiesthenumberofcharsinthelpRect:PointstoaRECTstructureorCRectobjectthatcontainstherectangle(inlogicalcoordinates)inwhichthetextistobeformatted.str:ACStringobjectthatcontainsthespecifiedcharacterstobedrawn.nFormat:Specifiesthemethodofformattingthetext.CallthismemberfunctiontoformattextinthegivenTheParameternFormatcanbeanycombinationofthefollowingExample:DrawText&CRectpDC->DrawText("單行文本居中rc,DT_CENTER|DT_VCENTERinab=40;pDC->TabbedTextOut(rc.left,rc.top,"繪制\tTab\t文本\t示例1,&nTab,pDC->TabbedTextOut(rc.left,rc.top+20,"繪制\tTab\t文本\t示例1,&nTab,pDC->TabbedTextOut(rc.left,rc.top+40,"繪制\tTab\t文本\t示例0,UINTSetTextAlign(UINTnFlagsThenFlagsvalueisoneormoreofthefollowingvalues:CDC::GetTextAlignUINTGetTextAlign()const;Thereturnvalueisoneormoreofthefollowingvalues:AllCDCtextfunctionsusethefontthatiscurrentlyselectedintothedevicecontext.Afontisagroupofcharactersofaparticularsize(height)andtypefacethatsharecommonattributessuchascharacterweight—forexample,normalorboldface.FontsareanintegralpartoftheWindowsGDI.ThismeansthatfontsbehavethesamewayotherGDIobjectsdo.Theycanbescaledandclipped,andtheycanbeselectedintoadevicecontextasapenorabrushcanbeselected.AllGDIrulesaboutdeselectionanddeletionapplytofonts.GetTextMetricsletyouretrieveinformationaboutthefontthatiscurrentlyselectedintothedeviceGetTextMetricsfillsaTEXTMETRICstructurewithinformationonthecharactersthatmakeuptheFivefontheightmeasurementparamet