资料案例介绍

SE-341Computer(SpringSE-341Computer(Spring&hidden-••••HiddenSurface•Clippingof•ClippingofprimitivesisdoneusuallyscanconvertingtheprimitivesReasonsbeingscanconversionneedstodealonlywiththeversionoftheprimitive,whichmightbemuchsmallerthanitsunclippedversionPrimitivesareusuallydefinedintherealworld,theirmappingfromtherealtotheintegerdomainofthedisplaymightresultintheoverflowingoftheintegervaluesresultinginunnecessary•HowwouldweHowwouldwe••••2D3DClippingiseasyforLineandPolygonsClippingishardforcurveandText–Theycanbetransformedto2D2DClipping2D2DClipping2D2DClippingSegment-Segment-IntersectionIntersectionwithaxis-aligned2DClipping2DClipping•••••Sutherland-Cohen裁剪：编中点分割裁剪：除以2，移位运参数化裁剪与梁友栋-Barsky裁剪：高效率的裁Nicholl-Lee-Nicholl裁剪：更为精细的判(outcode1OR(outcode1ORoutcode2)==linesegmentis(outcode1ANDoutcode2)!=linesegmentistotally(outcode1ANDoutcode2)==linesegmentpotentiallycrossesclipFalseSomelinesegmentsthatareclassifiedascrossingtheclipregionactuallyCheckLineCheckLineIfP1P2iscompletelyinside,acceptit;ifP1P2isoutside,rejectit;otherwisegotostepFindanendpointP1(orP2)oflineP1P2outsideofFindtheintersectionpointP’1toreplaceP1(orIfP1P2iscompletelyinside,thenacceptthisline,elsetostep3D3DPipelinePipelinesystemofLinePolygonPolygonPolygonPolygonPolygonPolygonBoundingBoundingBoundingBounding••••HiddenSurfaceWhyeliminatinginvisibleWhyeliminatinginvisible••VisibleandinvisibleportionsofEnhancereality(增加图形的真实感Projectionÿ3Dspace2D2Dspaceÿsortingaccordingtodepthmayadd3DWhyeliminatinginvisibleWhyeliminatinginvisibleHiddensurfaceremoval(HSR)mayBC(a)CubeBisthenearestĀ(c)CtheVisibleSurfaceVisibleSurfaceGiven:asetof3DobjectsandViewing Determine:thosepartsoftheobjectsthatarevisiblewhenviewedalongthedirectionofprojection.Orequivalently,eliminationofhiddenparts(hiddenlinesandsurfaces)Visiblepartswillbedrawn/shownwithpropercolorsandshads.•••Hiddensurface•ImageHiddensurface•ImageSpaceMethodÿ图像空间 Workonper-pixel/peroffragmentafterscanMuchfaster,butresolutionZ-Buffer/DepthObjectSpaceMethodÿ对象空间Workin3DbeforescanUsuallyindependentofImportanttomaintainindependenceofoutputdevice(screen/printeretc.)FrameworkofFrameworkofHSRinimagefor(Eachpixelintheimage)connectthepixelandtheviewpointfindthenearestobjectĀcomputethecolorforthe}•Theimageis•Theimageisconstrainedbyresolutionofdisplaydevices受分辨率限制)ComplexityO(nN)ÿObjectsshouldbesortedforeachpixelusen:thenumberofprimitivesN:thenumberofAlgorithmsÿz-buffer,scanline••FrameworkofHSRinFrameworkofHSRinobjectfor(eachobjectinworldcoordinate{determinethosepartsoftheobjectviewisunobstructedbyotherpartsofitoranyotherobject;drawthosepartsintheappropriate}•Highresolution•Highresolution (适合于精密的CAD工程领域•ComplexityEachobjectshouldbecomparedwiththeothern:objectBacksurface••理论–如n(物体数•理论–如n(物体数)<N(像素数，则对象空间算法的计O(n2)小于图像空间算法对象空间和图像空间的混合消隐••Hiddensurface•ImageHiddensurface•ImageSpaceZ-Buffer/DepthObjectSpaceZ-bufferZ-bufferZ-bufferFrame-buffer:Z-bufferFrame-buffer:storethecolorofZ-bufferÿstorez-coordinatesofViewingsystem(oxyzprojectionplanez=0;viewingdirection(0,0,-1);orthogonalprojection(平行投影)Depthvalueofapointisitsz-Thelargerofthez-valuetheshorterofthedistancetotheviewpoint(z越大离视点越近)•DepthColorDepthColorOutlineofz-Initializecolor(frame)-bufferOutlineofz-Initializecolor(frame)-bufferbackgroundInitializez-buffer视点最远的z以任意顺序扫描各多a)对于多边形中的每一像素，计算其深度值比较z(x,y)与z缓冲器中已有的值如果z(x,y)zbuffer(x,y)计算该像素y)的光亮值属性并写入帧缓更新zzbuffer(x,Z-BufferZ-BufferZ-BufferZ-BufferZ-BufferZ-BufferObjectObjectSpaceBackBackfaceBackface•LetBackface•LetVbetheviewingdirectionfromthetothecamera;nthenormalofthefacetobe––BackBackface•Only•Onlyapplicabletoconvex•Only•OnlyapplicabletoconvexPainter’sPainter’sForFor2DForFor2DForFor2DPainter’sPainter’sWhatPainter’sPainter’sWhatPainter’sPainter’sBinaryBinarySpacePartitioningBinaryBinarySpacePartitionCreatingCreatingBSPTrees:CreatingCreatingBSPTrees:CreatingCreatingBSPTrees:CreatingCreatingBSPTrees:CreatingCreatingBSPTrees:SplittingSplittingBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-Trees:ViewpointBSP-Trees:BSP-