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30340;纹理缓冲.】Additiveimpliesthatthesceneisrenderedoncefromthecameraperspectiveandthecontributionofeachlightisaccumulatedintothefinalrender.Thistechniquecreatesgoodresultsbutisalsoreallyexpensivebecauseeachlightaddsanotherrenderingrun.Wewon'tgointodetailsonhowshadowsworkbecausethisisaplexfield.Manybookscouldbewrittenaboutthistopic,andalso,shadowtechniqueschangerapidlyandareheavilyresearched.Ifyouareinterestedinthistopic,youcanfindinterestingarticlesintheNVIDIAbookseriesGPUGems,theShaderXbookseries,andintheproceedingsoftheSiggraphconference(siggraph./).
【Additive意味着场景在画面视角你可以NVIDIA的有关GPU的宝石系列丛书ShaderX系列丛书中有意义的文章Siggraph(计算机图形图像特别兴趣小组会议记录siggraph./).】
Creatingacamera
【创建一个摄像机】
Sofar,wehavealwaysusedacamerathatwascreatedforusebythe
ExampleApplication.Nowlet'screateoneforourselves.Acamera,asthenamesuggests,
capturesapartofourscenefromacertainposition.Therecanonlybeonecameraactive
ataparticulartimebecauseweonlyhaveoneoutputmedium,thatis,ourmonitor.Butitis
possibletouseseveralcamerasinonescenewheneachoneisrenderedaftertheother.
【目前为止,我们总是使用ExampleApplication类中创建的摄像机.现在让我们自己创建一个摄像机.摄像机,顾名思义在某一特定时间显示器Timeforaction–creatingacamera
【实践时刻——创建一个摄像机】
Thistimewewon'tmodifythecreateScene()function,sojustleaveitasitiswiththe
Sinbadinstanceandshadows:
【这次我们不修改createScene()函数,所以保留Sinbad的实例和阴影.】
CreateanewemptyfunctionnamedcreateCamera()intheExampleApplicationclass:
【在ExampleApplication中创建一个新的名为createCamera()的空函数】
voidcreateCamera(){
}
CreateanewcameranamedMyCamera1andassignittothemembermCamera:
【2.创建一个新的称为MyCamera1的摄像机并把它分配给数据成员mCamera:】
mCamera等于mSceneMgr->,createCamera("MyCamera1"),
Setthepositionofthecameraandletitlookatthenullpoint:
【3.设置摄像机的位置并让其镜头朝向原点:】
mCamera->,setPosition(0,100,200),
mCamera->,lookAt(0,0,0),
mCamera->,setNearClipDistance(5),
Nowchangetherendermodetowireframemodus:
【4.现在改变渲染模式至线框模式】
mCamera->,setPolygonMode(Ogre::PM_WIREFRAME),
Compileandruntheapplication.
【5.编译运行程序.】
Whatjusthappened
【刚刚发生了什么】
WeoverrodethecreateCamera()function,whichinitiallycreatedacameraandsetit
toaposition.Aftercreation,wesetapositionandusedthelookat()functiontosetthe
camerauptolookattheorigin.Thenextstepwedidwassettingthenearclippingdistance.
【我们重写了最初创建摄像机的createCamera()函数并设置它到一个位置.在创建之后,我们设置完它的位置并且使用lookat()函数以设置摄像机的镜头对准原点.我们所做的下一步是设置剪裁的距离.】
Acameracanonlyseepartsofa3Dscene,sorenderingitpletelywouldbeawasteof
preciousCPUandGPUtime.Topreventthis,beforerendering,largepartsofthesceneare
"cutout"fromthescenebytheSceneManager.Onlyobjectsvisibletothecameraare
rendered.Thisstepiscalledculling.Onlythoseobjectsthatarebeforethenearclipping
planeandbehindthefarclippingplanearerenderedandthenonlywhentheyareinsidea
pyramid,thisiscalledtheviewfrustumofthecamera.Theviewfrustumisapyramidwith
thetopcutoff,onlythoseobjectsthatareinsidethecut-offpyramidcanbeseenbythe
camera.Moreinformationcanbefoundatlighthouse3d./opengl/
viewfrustum/.Wesetthenearclippingplaneto5.Whenyouuseahigher-valuepartof
thescenewhichisnearthecamera,itwillbeculledandnotvisible.
【一个摄像机只可以看到部分的3D场景.因为完整渲染需要浪费宝贵的CPU和GPU时间.为避免这种情况SceneManager)将会把大部分的场景从场景中裁剪出去.只有摄像机的课件部分被渲染到.这一步叫做拣选.只有位于远近裁剪面并且在视锥体内部的物体才会被渲染.这被称为摄像机的视锥.视锥没有顶部的锥体.只有在剪裁过的锥体内部的对象才能被摄像机所看到.更多信息可在lighthouse3d./opengl/viewfrustum/中找到】
Thenwechangedtherendermodetowireframe.ThiseffectthatwegetwhenwepresstheRkey,assuggestedbefore,isthesameastheonewegotwhenwewantedtoseetheplanetriangles.WithR,thiseffectcanalsobeundone.Whentheapplicationstarts,wenowseeadifferenceasparedtoearlier,thecameraisnowabovetheinstanceofSinbadandlooksdownonhim.
【然后我们改变渲染模式为线框模式.】
BeforeoverridingthecreateCamera()function,thecamerastartedhoveringslightlyovertheplanelookingattheorigin.WithsetPosition(0,100,200),
wesetthecamerahigherthanbefore,thefollowingscreenshotshowsthechange.Oneinterestingaspectwecanobserveisthatevenafterwehavecreatedourowninstanceofacamera,wecanstillnavigatethesceneasbefore.ThisispossiblebecauseweusedthemCameramembervariablefromExampleApplication.ThiskeepsExampleApplicationincontrolofourcameraandthusitcanbemodified.Oneimportantfeatureofacameraisthatitcanalsobeattachedtoascenenodeandwillreactthesamewayanentitydoeswhenattachedtoascenenode.
【在重写createCamera()函数之前,摄像机的起始位置是悬停在平面上方一点,镜头朝向原点.使用setPosition(0,100,200),设置我们的摄像机到更高的位置.下面的截图显示了改变的效果.】
Haveagohero–doingmorewiththething
【让英雄动起来——做更多的事】
Tryusingdifferentpositionsandlookatpointstoseehowthisaffectsthestartingpositio
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