Android开发之OpenGL教程.docx

Android开发之OpenGL教程.docx

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Android开发之OpenGL教程

OpenGLESTutorialforAndroid

–PartI

I'mgoingtowriteacoupleoftutorialsonusingOpenGLESonAndroidphones.ThetheoryofOpenGLESisthesameondifferentdevicessoitshouldbequiteeasytoconvertthemtoanotherplatform.

Ican'talwaysrememberwhereIfoundparticularinfosoImightnotalwaysbeabletogiveyoutherightreference.IfyoufeelthatIhaveborrowedstufffromyoubuthaveforgottentoaddyouasareference,pleasee-mailme.

InthecodeexamplesIwillhavetwodifferentlinksforeachfunction.TheactualfunctionwillbelinkedtotheandroiddocumentationandafterthatIwillalsolinktheOpenGLdocumentations.Likethis:

gl.glClearColor（0.0f,0.0f,0.0f,0.5f）;//OpenGLdocs.

So,let'sstart.

InthistutorialIwillshowyouhowtosetupyourOpenGLESviewthat’salwaysagoodplacetostart.

SettingupanOpenGLESView

SettingupaOpenGLviewhasneverbeenhardandonAndroiditisstilleasy.Therereallyareonlytwothingsyouneedtogetstarted.

GLSurfaceView

GLSurfaceViewisaAPIclassinAndroid1.5thathelpsyouwriteOpenGLESapplications.

∙ProvidingthegluecodetoconnectOpenGLEStotheViewsystem.

∙ProvidingthegluecodetomakeOpenGLESworkwiththeActivitylife-cycle.

∙Makingiteasytochooseanappropriateframebufferpixelformat.

∙Creatingandmanagingaseparaterenderingthreadtoenablesmoothanimation.

∙Providingeasy-to-usedebuggingtoolsfortracingOpenGLESAPIcallsandcheckingforerrors.

IfyouwanttogetgoingfastwithyourOpenGLESapplicationthisiswhereyoushouldstart.

Theonlyfunctionyouneedtocallonis:

publicvoidsetRenderer（GLSurfaceView.Rendererrenderer）

Readmoreat:

GLSurfaceView

GLSurfaceView.Renderer

GLSurfaceView.Rendererisagenericrenderinterface.Inyourimplementationofthisrendereryoushouldputallyourcallstorenderaframe.

Therearethreefunctionstoimplement:

//Calledwhenthesurfaceiscreatedorrecreated.

publicvoidonSurfaceCreated（GL10gl,EGLConfigconfig）

//Calledtodrawthecurrentframe.

publicvoidonDrawFrame（GL10gl）

//Calledwhenthesurfacechangedsize.

publicvoidonSurfaceChanged（GL10gl,intwidth,intheight）

onSurfaceCreated

Hereit'sagoodthingtosetupthingsthatyoudon'tchangesooftenintherenderingcycle.Stufflikewhatcolortoclearthescreenwith,enablingz-bufferandsoon.

onDrawFrame

Hereiswheretheactualdrawingtakeplace.

onSurfaceChanged

Ifyourdevicesupportsflippingbetweenlandscapeandportraityouwillgetacalltothisfunctionwhenithappens.Whatyoudohereissettinguppthenewratio.

Readmoreat:

GLSurfaceView.Renderer

Puttingittogether

Firstwecreateouractivity,wekeepitcleanandsimple.

packagese.jayway.opengl.tutorial;

importandroid.app.Activity;

importandroid.opengl.GLSurfaceView;

importandroid.os.Bundle;

publicclassTutorialPartIextendsActivity{

/**Calledwhentheactivityisfirstcreated.*/

@Override

publicvoidonCreate（BundlesavedInstanceState）{

super.onCreate（savedInstanceState）;

GLSurfaceViewview=newGLSurfaceView（this）;

view.setRenderer（newOpenGLRenderer（））;

setContentView（view）;

}

}

Ourrenderertakeslittlebitmoreworktosetup,lookatitandIwillexplainthecodeabitmore.

packagese.jayway.opengl.tutorial;

importjavax.microedition.khronos.egl.EGLConfig;

importjavax.microedition.khronos.opengles.GL10;

importandroid.opengl.GLU;

importandroid.opengl.GLSurfaceView.Renderer;

publicclassOpenGLRendererimplementsRenderer{

/*

*（non-Javadoc）

*

*@see

*android.opengl.GLSurfaceView.Renderer#onSurfaceCreated（javax.

*microedition.khronos.opengles.GL10,javax.microedition.khronos.

*egl.EGLConfig）

*/

publicvoidonSurfaceCreated（GL10gl,EGLConfigconfig）{

//Setthebackgroundcolortoblack（rgba）.

gl.glClearColor（0.0f,0.0f,0.0f,0.5f）;//OpenGLdocs.

//EnableSmoothShading,defaultnotreallyneeded.

gl.glShadeModel（GL10.GL_SMOOTH）;//OpenGLdocs.

//Depthbuffersetup.

gl.glClearDepthf（1.0f）;//OpenGLdocs.

//Enablesdepthtesting.

gl.glEnable（GL10.GL_DEPTH_TEST）;//OpenGLdocs.

//Thetypeofdepthtestingtodo.

gl.glDepthFunc（GL10.GL_LEQUAL）;//OpenGLdocs.

//Reallyniceperspectivecalculations.

gl.glHint（GL10.GL_PERSPECTIVE_CORRECTION_HINT,//OpenGLdocs.

GL10.GL_NICEST）;

}

/*

*（non-Javadoc）

*

*@see

*android.opengl.GLSurfaceView.Renderer#onDrawFrame（javax.

*microedition.khronos.opengles.GL10）

*/

publicvoidonDrawFrame（GL10gl）{

//Clearsthescreenanddepthbuffer.

gl.glClear（GL10.GL_COLOR_BUFFER_BIT|//OpenGLdocs.

GL10.GL_DEPTH_BUFFER_BIT）;

}

/*

*（non-Javadoc）

*

*@see

*android.opengl.GLSurfaceView.Renderer#onSurfaceChanged（javax.

*microedition.khronos.opengles.GL10,int,int）

*/

publicvoidonSurfaceChanged（GL10gl,intwidth,intheight）{

//Setsthecurrentviewporttothenewsize.

gl.glViewport（0,0,width,height）;//OpenGLdocs.

//Selecttheprojectionmatrix

gl.glMatrixMode（GL10.GL_PROJECTION）;//OpenGLdocs.

//Resettheprojectionmatrix

gl.glLoadIdentity（）;//OpenGLdocs.

//Calculatetheaspectratioofthewindow

GLU.gluPerspective（gl,45.0f,

（float）width/（float）height,

0.1f,100.0f）;

//Selectthemodelviewmatrix

gl.glMatrixMode（GL10.GL_MODELVIEW）;//OpenGLdocs.

//Resetthemodelviewmatrix

gl.glLoadIdentity（）;//OpenGLdocs.

}

}

Fullscreen

JustaddthislinesintheOpenGLDemoclassandyouwillgetfullscreen.

publicvoidonCreate（BundlesavedInstanceState）{

super.onCreate（savedInstanceState）;

this.requestWindowFeature（Window.FEATURE_NO_TITLE）;//（NEW）

getWindow（）.setFlags（WindowManager.LayoutParams.FLAG_FULLSCREEN,

WindowManager.LayoutParams.FLAG_FULLSCREEN）;//（NEW）

...//Previouscode.

}

Thisisprettymuchallyouneedtogetyourviewupandrunning.Ifyoucompileandrunityouwillseeaniceblackscreen.

OpenGLESTutorialforAndroid

–PartII

PrevioustutorialwasallaboutsettinguptheGLSurfaceView.Besuretoreaditbeacuseit'sareallyimportentonetobeabletocontinue.

Buildingapolygon

Inthistutorialwewillrenderourfirstpolygon.

3Dmodelsarebuiltupwithsmallerelements（vertices,edges,faces,andpolygons）whichcanbemanipulatedindividually.

Vertex

Avertex（verticesinplural）isthesmallestbuildingblockof3Dmodel.Avertexisapointwheretwoormoreedgesmeet.Ina3Dmodelavertexcanbesharedbetweenallconnectededges,pacesandpolygons.Avertexcanalsobearepresentforthepositionofacameraoralightsource.Youcanseeavertexintheimagebelowmarkedinyellow.

Todefinetheverticesonandroidwedefinethemasafloatarraythatweputintoabytebuffertogainbetterperformance.Lookattheimagetotherightandthecodebelowtomatchtheverticesmarkedontheimagetothecode.

privatefloatvertices[]={

-1.0f,1.0f,0.0f,//0,TopLeft

-1.0f,-1.0f,0.0f,//1,BottomLeft

1.0f,-1.0f,0.0f,//2,BottomRight

1.0f,1.0f,0.0f,//3,TopRight

};

//afloatis4bytes,thereforewemultiplythenumberifverticeswith4.

ByteBuffervbb=ByteBuffer.allocateDirect（vertices.length*4）;

vbb.order（ByteOrder.nativeOrder（））;

FloatBuffervertexBuffer=vbb.asFloatBuffer（）;

vertexBuffer.put（vertices）;

vertexBuffer.position（0）;

Don'tforgetthatafloatis4bytesandtomultiplyitwiththenumberofverticestogettherightsizeontheallocatedbuffer.

OpenGLEShaveapipelinewithfunctionstoapplywhenyoutellittorender.Mostofthesefunctionsarenotenabledbydefaultsoyouhavetoremembertoturntheonesyouliketouseon.Youmightalsoneedtotellthesefunctionswhattoworkwith.SointhecaseofourverticesweneedtotellOpenGLESthatit’sokaytoworkwiththevertexbufferwecreatedwealsoneedtotellwhereitis.

//Enabledthevertexbufferforwritingandtobeusedduringrendering.

gl.glEnableClientState（GL10.GL_VERTEX_ARRAY）;//OpenGLdocs.

//Specifiesthelocationanddataformatofanarrayofvertex

//coordinatestousewhenrendering.

gl.glVertexPointer（3,GL10.GL_FLOAT,0,vertexBuffer）;//OpenGLdocs.

Whenyouaredonewiththebufferdon'tforgettodisableit.

//Disabletheverticesbuffer.

gl.glDisableClientState（GL10.GL_VERTEX_ARRAY）;//OpenGLdocs.

Edge

Edgeisalinebetweentwovertices.Theyareborderlinesoffacesandpolygons.Ina3Dmodelanedgecanbesharedbetweentwoadjacentfacesorpolygons.Transforminganedgeaffectsallconnectedvertices,facesandpolygons.InOpenGLESyoudon'tdefinetheedges,youratherdefinethefacebygivingthemtheverticesthatwouldbuildupthethreeedges.Ifyouwouldlikemodifyanedgeyouchangethetwoverticesthatmakestheedge.Youcanseeanedgeintheimagebelowmarkedinyellow.

Face

Faceisatriangle.Faceisasurfacebetweenthreecornerverticesandthreesurroundingedges.Transformingafaceaffectsallconnectedvertices,edgesandpolygons.

Theorderdoesmatter.

Whenwindingupthefacesit'simportanttodoitintherightdirectionbecausethedirectiondefineswhatsidewillbethefrontfaceandwhatsidewillbethebackface.Whythisisimportantisbecausetogainperformancewedon'twanttodrawbothsidessoweturnoffthebackface.Soit'sagoodideatousethesamewindingalloveryourproject.ItispossibletochangewhatdirectionthatdefinesthefrontfacewithglFrontFace.

gl.glFrontFace（GL10.GL_CCW）;//OpenGLdocs

TomakeOpenGLskipthefacesthatareturnedintothescreenyoucanusesomethingcalledback-faceculling.Whatisdoesisdetermineswhetherapolygonofagraphicalobjectisvisiblebycheckingifthefaceiswindupinthe