《计算机图形学》总复习.ppt

计算机图形学总复习,ComputerGraphics,Ch1.asurveyofCS,ComputerGraphics,3,GraphicsConcept,Innarrowsense位图(bitmap)-图像Image，矢量图(vectorgraph)GraphicIngeneral,graphicscanbeanyobjectwhichisabletogivevisionimpressioninmansvisionsystem.Itincludevariousgeometrygraphics,views,pictures,patterns,andimages.,4,凡是能够在人的视觉系统中形成视觉印象的客观对象都称为图形。(1)自然景物(2)照片和图片(3)工程图、设计图和方框图(4)人工美术绘画、雕塑品(5)用数学方法描述的图形（包括几何图形、代数方程、分析表达式或列表所确定的图形）,什么是图形？,5,Vectorgraphandbitmap,(1).vectorgraph,Anycurvesareapproachedwithmanyshortlines,(2).bitmap,Everycurvemustbeconsistofseveralpixels,6,几何要素：刻画对象的轮廓、形状等(几何模型)非几何要素:刻画对象的颜色、材质等(物理属性),计算机图形学中的图形要素,7,WhatisComputerGraphics？,Thetechnologyforgeneratingtheimagesonthecomputerscreenwithalgorithmsandprogramsiscalledthecomputergraphics.计算机图形学(ComputerGraphics,CG)是研究怎样用数字计算机生成、处理和显示图形的一门学科。,8,Relationshipwithothersubjects,数字图像DigitalImages,数据模型DataModels,研究内容（学科）,9,ComputerGraphicsApplications,图形用户界面(GUI)计算机辅助设计与制造（CAD/CAM）娱乐游戏及计算机动画(entertainment/game/animation)计算机艺术(computerart)地理信息系统(GIS)科学技术与信息可视化(Visualization)虚拟现实(VirtualReality)图形用户界面(GUI),10,ResearchHotspot,真实感显示RealisticDisplay变形技术MorphingTechnology数字城市DigitalCity识别技术RecognizeTechnology基于图像的建模ImageBasedModeling自然对象的建模NatureObjectsModeling离散数据建模DiscreteDataModeling网络漫游Web3D,11,CRT(CathodeRayTube),Thebeamemitselectrons(cathode).Rayintensityiscontrolledbythegrid.Thefocusforcestheelectronstowardsaconvergencepath.Deflectorsforcetheraytopointataspecificscreenpoint.Theraystunsoverthephosphor.Phosphoremitslights.Phosphoremissiondeclinesveryfast(refreshmentrequired),Figure2-4ElectrostaticdeflectionoftheelectronbeaminaCRT,12,13,14,当前研究动态,(1)造型技术规则形体：欧氏几何方法不规则形体：分形几何方法、粒子系统、纹理映射实体造型基于物理的造型基于图像的造型,15,当前研究动态,(2)真实感图形绘制技术光照明模型绘制算法快速算法基于图像的绘制（非真实感图形绘制技术）,16,当前研究动态,(3)人机交互技术(4)与计算机网络技术的紧密结合远程医疗与诊断远程导航与维修远程教育,17,研究热点,ModelinggettingmodelsfromtherealworldAnimationphysicallybasedmodelingmotioncaptureRenderingmorerealistic:image-basedrenderinglessrealistic:impressionist,penglutInitDisplayMode(mode);glutInitWindowSize(500,500);glutCreateWindow(“Simple”);init();glutDisplayFunc(display);glutKeyboardFunc(key);glutMainLoop();,23,OpenGLInitialization,SetupwhateverstateyouregoingtouseDontneedthismuchdetailunlessworkingin3Dvoidinit(void)glClearColor(0.0,0.0,0.0,0.0);glViewport(0,0,width,height);glMatrixMode(GL_PROJECTION);glLoadIdentity();glOrtho(-10,10,-10,10,-10,20);glMatrixMode(GL_MODELVIEW);glLoadIdentity();glEnable(GL_LIGHT0);glEnable(GL_LIGHTING);glEnable(GL_DEPTH_TEST);,24,GLUTCallbackfunctions,Event-driven:ProgramsthatusewindowsInput/OutputWaituntilaneventhappensandthenexecutesomepre-definedfunctionsaccordingtotheusersinputEventskeypress,mousebuttonpressandrelease,windowresize,etc.YourOpenGLprogramwillbeininfiniteloop,25,GLUTCallbackFunctions,Callbackfunction:RoutinetocallwhenaneventhappensWindowresizeorredrawUserinput(mouse,keyboard)Animation(rendermanyframes)“Register”callbackswithGLUTglutDisplayFunc(my_display_func);glutIdleFunc(my_idle_func);glutKeyboardFunc(my_key_events_func);glutMouseFunc(my_mouse_events_func);,26,EventQueue,MainLoop(),27,RenderingCallback,CallbackfunctionwhereallourdrawingisdoneEveryGLUTprogrammusthaveadisplaycallbackglutDisplayFunc(my_display_func);/*thispartisinmain.c*/voidmy_display_func(void)glClear(GL_COLOR_BUFFER_BIT);glBegin(GL_TRIANGLE);glVertex3fv(v0);glVertex3fv(v1);glVertex3fv(v2);glEnd();glFlush();,28,IdleCallback,UseforanimationandcontinuousupdateCanuseglutTimerFuncortimedcallbacksforanimationsglutIdleFunc(idle);voididle(void)/*changesomething*/t+=dt;glutPostRedisplay();,29,UserInputCallbacks,ProcessuserinputglutKeyboardFunc(my_key_events);voidmy_key_events(charkey,intx,inty)switch(key)caseq:caseQ:exit(EXIT_SUCCESS);break;caser:caseR:rotate=GL_TRUE;break;,30,MouseCallback,CapturesmousepressandreleaseeventsglutMouseFunc(my_mouse);voidmyMouse(intbutton,intstate,intx,inty)if(button=GLUT_LEFT_BUTTONglColor3fv(color);glVertex2f(0.0,0.0);glVertex2f(1.0,0.0);glVertex2f(1.5,1.118);glVertex2f(0.5,1.118);glEnd();,Ch3.GeometricPrimitives几何图元绘制,ComputerGraphics,34,Whatisrastering?,Therasterdisplaytechnologyrequirestobrakedowngraphicprimitivesintopixelswithintheraster.Thisprocessiscalledrastering(栅格化).scanconversion（扫描转换）,Thisisusuallydonebythegraphicshardware.However,itisusefultounderstandhowthisprocessworksinordertobeabletoachievegoodgraphicsperformance.,35,扫描转换,将图形数字化为一组像素强度值，并存放在帧缓存中。这个数字化过程称为扫描转换(scanconversion)基本图元的扫描转换就是计算出落在基本图元上或充分靠近它的一串像素，并以此像素近似替代基本图元上对应位置在屏幕上显示的过程。,36,Line-DrawingAlgorithms,1)DDAalgorithm2)Bresenhamalgorithm,37,DDAalgorithm(p94),Thedigitaldifferentialanalyzer(DDA，数字微分分析法)isascan-conversionlinealgorithmbasedoncalculatingdifferencesbasedontheslopeoftheline.,38,DDAalgorithm,Alinecanbedescribedbytheequationy=mx+bWithoutlossofgenerality,wecanassume0m1.Otherwisewecanmirrororinterchangethecoordinatesasneeded.Now,weneedtocomputetheseriesofpoints(xk,yk),k=0,nthatbestdescribestheline.,39,DDAalgorithm,Since0mfabs(dy)steps=fabs(dx);elsesteps=abs(dy);xIncrement=(float)(dx)/steps;yIncrement=(float)(dy)/steps;For(k=0;k1,swapthecoordinatesaxes.,42,42,AdvantageandDisadvantageforDDA,Advantage优点:-消除乘法.Disadvantage缺点:-浮点数相加积累误差，对长线段而言，引起像素点位置与理想位置的偏移.-需要圆整操作和浮点计算，消耗时间。,43,DDAalgorithm,TheDDAalgorithmeasilycanbeextendedtoothergraphicsprimitives,suchascircles,ellipses,etc.DDAisGood,butStillNotFastEnough!Floatingpointmultiplygonefromy=mx+bButloopstillhasafloatingpointaddAndaround()WECANDOBETTER!Bestperformance:Onlyintegeradds/subtractsinsideloopTheBresenhamalgorithmallowsustodojustthat.,44,Bresenhamalgorithm(p95),Again,weassumewithoutlossofgeneralitythattheslopeis0m1;hence,thelineislocatedinthefirstoctant.,Ideanomatterwhattheslopeis,weincreaseonecoordinatebyone(x-coordinate)similartotheDDAalgorithm.Theothercoordinate(y-coordinate)iseitherincreasedbyoneaswellorleftunchanged,dependingonthedistancetothenextgridpoint.,45,Bresenhamalgorithm,Inordertodecidewhichpointtopick,weintroduceanerrorEwhichisproportionaltothedifferencebetweentheexactpointonthestraightlineandthecenterbetweenthetwopossiblegridpointsontheraster.ThesignofEcanthenbeusedasacriterionforthedecision.,Eitherpoint1orpoint2isdrawn,dependingonwhichisclosertothestraightline.,46,Bresenhamalgorithm,47,Bresenhamalgorithm,IfwescaleEusingx,thenwecaneliminatem.,48,Bresenhamalgorithm,CanEkbecaculatedrecursively?Yes!,49,Bresenhamalgorithm,Note:ONLYintegeroperationsareused!,BresenhamAlgorithm/(x1,y1),(x2,y2),x1x2x=x1;y=y1;dx=x2-x1;dy=y2-y1;e=2*dy-dx;setPixel(x,y);while(xx2)x=x+1;if(e0)e=e+2*dy;elsee=e+2*dy-2*dx;y=y+1;setPixel(x,y);,50,Bresenhamalgorithm,dx=5,dy=4,2*dy=8,2*dy-2*dx=-2E0=2*dy-dx=3,if(e0)e=e+2*dy;elsee=e+2*dy-2*dx;y=y+1;,51,MidpointCircleAlgorithm(Hearnx=0;y=int(radius);h=1-int(radius);Set8Pixel(x0,y0,x,y);/CirclePlotPointswhile(xy)x+;if(h0)h+=2*x+1;elsey-;h+=2*(x-y)+1;Set8Pixel(x0,y0,x,y);,60,Circlesnotcenteredonorigin,NewSet8Pixel()Function:,Ch4.AttributesofGeometricPrimitives几何图元的属性,ComputerGraphics,1.AreaFillAlgorithms(区域填充算法),(HearnSection4-10/11/12/13,P196),63,Scan-linemethods(扫描线填充算法),WorksrowbyrowfromtoptobottomApixelinsidethecurrentscanlineisonlydrawnifitislocatedinsidethepolygon.,逐点判断法,Greedyapproachveryslow!,64,Coherence,EdgeCoherence(边的连贯性)某条边与当前扫描线相交，也可能与下一条扫描线相交Scan-lineCoherence(扫描线的连贯性)当前扫描线与各边的交点顺序与下一条扫描线与各边的交点顺序可能相同或类似SpanCoherence(区间的连贯性)同一区间上的像素取同一颜色属性,65,Scan-linemethods:Example,Example:Scanliney=2:-intersectionwithpolygonatx=1,8-wecansubdividethescanlineinto3sections:,66,Scan-linemethods:Example,Example:Scanliney=4:-intersectionwithpolygonatx=1,4,6,8-wecansubdividethescanlineinto5sections:,67,Scan-linemethods,Thesimpleorderededgelistalgorithm(有序边表算法)Method:preprocessing+scanconversion,68,OrderedEdgeListAlgorithm,Preprocessing(1)Determ