OpenGLOpenGL

CPRE388

OpenGLOpenGL

Open Graphics LibraryOpenGraphicsLibrary Developedin1992bySiliconGraphicsC ll i f 300 Collectionofover300APIs

HidesthedetailsofGPUs(hardwaregraphicsaccelerators).

Graphics PipelineGraphicsPipeline

OpenGLp basicoperationistoacceptprimitivessuchaspoints lines and polygons and convert thempoints,linesandpolygons,andconvertthemintopixels.

h d b h l k ThisisdonebyagraphicspipelineknownastheOpenGLStateMachine.

Some TermsSomeTerms

Pixel picture element is a single point in aPixel pictureelement isasinglepointinarasterimage.

pixel is the smallest addressable screen pixelisthesmallestaddressablescreenelement

l i i ll d b h f coloristypicallyrepresentedbythreeorfourcomponentintensitiessuchasred,greenandbl ll d bl kblue,orcyan,magenta,yellowandblack.

RasterizationRasterization

task of taking an image described in a vectortaskoftakinganimagedescribedinavectorgraphicsformat(shapes)andconvertingitintoa raster image (pixels or dots) for output on aarasterimage (pixels ordots)foroutputonavideodisplay orprinter,orforstorageinabitmap file formatbitmapfileformat.

OpenGLTransformationSupport Three matrices Threematrices

GL_MODELVIEW,GL_PROJECTION,GL_TEXTURE glMatrixMode(mode) specifiestheactivematrix

glLoadIdentity() Settheactivematrixtoidentity

glLoadMatrix{fd}(TYPE *m)glLoadMatrix{fd}(TYPE m) Setthe16valuesofthecurrentmatrixtothosespecifiedbym

m1 m5 m9 m13m2 m6 m10 m14m3 m7 m11 m15

m =

glMultMatrix{fd}(TYPE*m) Multipliesthecurrentactivematrixbym

m4 m8 m12 m16

TransformationExample

glMatrixMode(GL_MODELVIEW);

glLoadIdentity();//matrix=I

lM ltM t i (N) // t i NglMultMatrix(N);//matrix=N

glMultmatrix(M);//matrix=NM

glMultMatrix(L); // matrix = NMLglMultMatrix(L);//matrix=NML

glBegin(GL_POINTS);

glVertex3f(v);//vwillbetransformed:NMLvg f( ); //

glEnd();

OpenGLTransformations

glTranslate{fd}(TYPEx,TYPEy,TYPEz) Multiplythecurrentmatrixbythetranslationmatrix

glRotate{fd}(TYPEangle,TYPEx,TYPEy,TYPEz) Multiplythecurrentmatrixbytherotationmatrixthatrotatesanobjectabouttheaxisfrom(0,0,0)to(x,y,z)

glScale{fd}(TYPEx,TYPEy,TYPEz) Multiplythecurrentmatrixbythescalematrix

ExamplesExamples

glMatrixMode(GL MODELVIEW);glMatrixMode(GL_MODELVIEW);

glRecti(50,100,200,150);

glTranslatef(200.0, 50.0, 0.0);glTranslatef( 200.0, 50.0,0.0);

glRecti(50,100,200,150);

glLoadIdentity();g y()

glRotatef(90.0,0.0,0.0,1.0);

glRecti(50,100,200,150);

glLoadIdentity();

glscalef(.5,1.0,1.0)

glRecti(50,100,200,150);

Viewingin3D World (3D) Screen (2D)World(3D) Screen(2D) OrientingEyecoordinatesysteminWorldcoordinate systemcoordinatesystem ViewOrientationMatrix

Specifyingviewingvolumeandprojectionparametersforn d(d

WorldtoEyeCoordinates

Weneedtotransformfromtheworldcoordinatestotheeyecoordinates

Theeyecoordinatesystemisspecifiedby: Viewreferencepoint(VRP)

(VRPx,VRPy,VRPz)

Directionoftheaxes:eyecoordinatesystem U =(ux,uy,uz)

V =(vx,vy,vz)

N ( ) N =(nx,ny,nz)

WorldtoEyeCoordinates

Therearetwostepsinthetransformation(in order)(inorder) Translation Rotation Rotation

WorldtoEyeCoordinates

TranslateWorldOrigintoVRP

1 0 0 VRP xa 1 0 0 -VRPx0 1 0 -VRPy0 0 1 -VRPz0 0 0 1

xyz1

abc1

=

0 0 0 1 11

WorldtoEyeCoordinates

RotateWorldX,Y,ZtotheEyecoordinatesystemu,v,n,alsoknownastheViewR f C diReferenceCoordinatesystem

ax u u u 0 abc1

xyz1

=

ux uy uz 0vx vy vz 0nx ny nz 00 0 0 1 11 0 0 0 1

DrawingDrawing

OpenGL primitives glVertex, glLine,OpenGLprimitives glVertex,glLine,glTriangle

glVertex2f(100.0f, 150.0f); defines a point at xglVertex2f(100.0f,150.0f);definesapointatx=100,y=150,z=0;thisfunctiontakesonly2parameters,zisalways0.

glVertex3f(100.0f,150.0f,25.0f);definesapointatx=100,y=150,z=25.0f;thisfunctiontakes3parameters,definingafully3Dpointinyourworld

glVertex alonewon'tdrawanythingonthescreenlB i (i t d ) d lE d( id ) glBegin(intmode);andglEnd(void );

TheparametermodeofthefunctionglBegin canbe one of the following:beoneofthefollowing:GL_POINTSGL LINESGL_LINESGL_LINE_STRIPGL_LINE_LOOPGL_TRIANGLESGL_TRIANGLE_STRIPGL TRIANGLE FANGL_TRIANGLE_FANGL_QUADSGL QUAD STRIPG _QU _SGL_POLYGON

//thiscodewilldrawapointlocatedat[100,100,25]

glBegin(GL_POINTS);

glVertex3f(100.0f,100.0f,25.0f);

glEnd( );glEnd();

// Thi d ill d li t t ti d//ThiscodewilldrawalineatstartingandendingcoordinatesspecifiedbyglVertex3f

glBegin(GL_LINES);glVertex3f(100.0f,100.0f,0.0f);//originoftheline

glVertex3f(200.0f,140.0f,5.0f);//endingpointoftheline

glEnd();

//thefollowingcodedrawsatriangle

l i ( )glBegin(GL_TRIANGLES);glVertex3f(100.0f,100.0f,0.0f);

glVertex3f(150.0f,100.0f,0.0f);

glVertex3f(125.0f,50.0f,0.0f);

glEnd();g ( );

//thiscodewilldrawtwolines"atatime"tosave//thetimeittakestocallglBegin andglEnd.glBegin(GL_LINES);glVertex3f(100.0f,100.0f,0.0f);//originoftheFIRSTlineglVertex3f(200.0f,140.0f,5.0f);//endingpointofh ltheFIRSTlineglVertex3f(120.0f,170.0f,10.0f);//originoftheSECOND liSECONDlineglVertex3f(240.0f,120.0f,5.0f);//endingpointofthe SECOND linetheSECONDline

glEnd();

OpenGL Viewer PerspectiveOpenGLViewerPerspective

ViewerViewer

when OpenGL is initialized and the projectionwhenOpenGLisinitializedandtheprojectionissetupweareinitiallylookingdownthenegative Z spacenegativeZspace

Thepointx=0,y=0,z=0isintheexactcenterof the screenofthescreen

voidRenderFrame (void){glClear(GL COLOR BUFFER BIT|GL DEPTglClear(GL_COLOR_BUFFER_BIT|GL_DEPT

H_BUFFER_BIT);glBegin(GL TRIANGLES);glBegin(GL_TRIANGLES);glVertex3f(1.0f,0.5f,4.0f);//lowerleftvertexvertexglVertex3f(1.0f,0.5f,4.0f);//lowerrightvertexvertexglVertex3f(0.0f,0.5f,4.0f);//uppervertexlE d()glEnd();}

glBegin(GL_TRIANGLES);

glVertex3f(1.0f,0.5f,4.0f);//lowerleftvertex

glVertex3f(1.0f,0.5f,4.0f);//lowerrightvertexvertex

glVertex3f(0.0f,0.5f,4.0f);//uppervertex

lV t 3f( 0 5f 1 5f 4 0f)glVertex3f(0.5f,1.5f,4.0f);

glVertex3f(0.5f,1.5f,4.0f);

glVertex3f(0.0f,1.0f,4.0f);

glEnd();glEnd();

StripsStrips

a call to glVertex takes some time to processacalltoglVertex takessometimetoprocess minimizethenumberofcallstoglVertex whiledrawing the same amount of primitives be it adrawingthesameamountofprimitivesbeitalineoratriangleoraquad

GL LINE STRIP GL_LINE_STRIPGL_TRIANGLE_STRIPGL QUAD STRIPGL_QUAD_STRIP

Triangle StripTriangleStrip

glBegin(GL_TRIANGLE_STRIP);

glVertex3f(1.0f,0.5f,4.0f);//A

glVertex3f( 1.0f, 0.5f, 4.0f); // BglVertex3f(1.0f, 0.5f, 4.0f);//B

glVertex3f(0.0f,0.5f,4.0f);//C

lV t 3f(1 5f 0 0f 4 0f) // DglVertex3f(1.5f,0.0f,4.0f);//D

glVertex3f(2.0f,1.5f,4.0f);//E

glEnd();

Triangle FansTriangleFans

A triangle fan has one origin indicated by theAtrianglefanhasoneoriginindicatedbythefirstvertex,andaninitialtriangle,indicatedbythe first 3 vertices including the originthefirst3verticesincludingtheorigin.

Asyouaddthe4thand5thverticestoyoufan you continue it just like you did with afan,youcontinueitjustlikeyoudidwithatrianglestrip.

Triangle FanTriangleFan

glBegin(GL_TRIANGLE_FAN);

glVertex3f(1.0f,0.5f,4.0f);//A

glVertex3f(1.0f,0.5f,4.0f);//Bg ( , , );

glVertex3f(0.0f,0.5f,4.0f);//C

glVertex3f( 1 5f 0 0f 4 0f); // DglVertex3f(1.5f,0.0f,4.0f);//D

glVertex3f(1.8f,1.0f,4.0f);//E

glVertex3f(0.2f,1.5f,4.0f);//F

glVertex3f(1.0f,0.5f,4.0f);//Gg

glEnd();

OpenGLESOpenGL ES

OpenGL ES 1 1 implements the standardOpenGLES1.1implementsthestandardgraphicspipelinewithawelldefinedfixedfunction pipelinefunctionpipeline

OpenGLES2.0removesallfunctionsthatacton the fixed function pipeline replacing itonthefixedfunctionpipeline,replacingitwithageneralpurposeshaderbasedpipeline

A l ff h d h b h AppleoffershardwarethatsupportsbothOpenGLES1.1andOpenGLES2.0.

Core Animation is fundamental to the iOSCoreAnimationisfundamentaltotheiOSgraphicssubsystem,includingOpenGLES

Every UIView object in your application is EveryUIView objectinyourapplicationisbackedbyaCoreAnimationlayer

O GL ES i l d d yourOpenGLEScontentisalsorenderedtoaCoreAnimationlayersothatitcanbe

i d i h hcompositedwithothercontent

OpenGLESObjectsh b l d b h Atextureisanimagethatcanbesampledbythe

graphicspipeline.Thisistypicallyusedtomapacolor image onto your geometry but can also becolorimageontoyourgeometrybutcanalsobeusedtomapotherdataontothegeometry

AbufferisasetofmemoryownedbyOpenGLESth t li ti d it d t i tthatyourapplicationcanreadorwritedatainto.Themostcommonuseforabufferistoholdvertexdatathatyourapplicationwantstosubmity pptothegraphicshardware.

Shaders arealsoobjects.AnOpenGLES2.0application creates a shader compiles and linksapplicationcreatesashader,compilesandlinkscodeintoit,andthenassignsittoprocessvertexandfragmentdata.

A renderbuffer is a simple 2D graphics image Arenderbuffer isasimple2Dgraphicsimageinaspecifiedformat.Thisformatmaybedefinedascolordata,butitcouldalsobedepthorstencilinformation.Renderbuffersarenotusuallyusedalone,butareinsteadll d d d f f b ffcollectedandusedaspartofaframebuffer.

Framebuffers aretheultimatedestinationofh hi i li A f b ff bj ithegraphicspipeline.Aframebuffer objectisreallyjustacontainerthatattachestexturesand renderbuffers to itself to create aandrenderbuffers toitselftocreateacompletedestinationforrendering.

reducethecomplexityofyourgeometrybyusingsomeofthefollowingtechniques

Provide multiple versions of your geometry at Providemultipleversionsofyourgeometryatdifferentlevelsofdetail,andchooseanappropriatemodelbasedonthedistanceofpp ptheobjectfromthecamera.

UseInterleavedVertexData Interleaveddataprovidesbettermemorylocalitythanusingaseparatearrayforeachattribute.

UseTriangleStrips Usingtrianglestripssignificantlyreducesthenumberofvertexcalculations that OpenGL ES must perform oncalculationsthatOpenGLESmustperformonyourgeometry.Yourperformanceisbestifanobject (or even a group of objects) can beobject(orevenagroupofobjects)canbesubmittedinasingleunindexed trianglestripusingglDrawArrays.Thismayinvolveaddingdegeneratetrianglestomergemultiplesmallertrianglestripsintoasinglelargestrip.

UseVertexBuffers Bydefault,anapplicationmaintainsitsownvertexdataandsubmitsittothehardwaretoberendered.Whenyousubmitgeometry,itiscopiedtothehardwaretoberendered

typedef struct _vertexStruct{{

GLfloat position[2];GLubyte color[4];

} vertexStruct;}vertexStruct;voidDrawGeometry(){const vertexStruct vertices[] = { };constvertexStruct vertices[]={...};constGLubyte indices[]={...};

glEnableClientState(GL_VERTEX_ARRAY);lV t P i t (2 GL FLOAT i f( t St t)glVertexPointer(2,GL_FLOAT,sizeof(vertexStruct),&vertices[0].position);glEnableClientState(GL_COLOR_ARRAY);glColorPointer(4 GL UNSIGNED BYTE sizeof(vertexStruct)glColorPointer(4,GL_UNSIGNED_BYTE,sizeof(vertexStruct),

&vertices[0].color);glDrawElements(GL_TRIANGLE_STRIP,sizeof(indices)/sizeof(GLubyte),GL UNSIGNED BYTE indices);GL_UNSIGNED_BYTE,indices);

}

E h ti lD El t i ll d th d t EachtimeglDrawElements iscalled,thedataisretransmittedtothegraphicshardwaretob d dberendered

Ifthedatadidnotchange,thoseadditionalcopiesareunnecessary

CreatingVertexBufferstypedef struct vertexStructtypedef struct _vertexStruct{GLfloat position[2];p [ ];GLubyte color[4];

}vertexStruct;constvertexStruct vertices[]={...};constGLubyte indices[]={...};GLuint vertexBuffer;GLuint vertexBuffer;GLuint indexBuffer;voidCreateVertexBuffers(){glGenBuffers(1,&vertexBuffer);

glGenBuffers(1,&indexBuffer);glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer);glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,indexBuffer);glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(indices),indices,GL_STATIC_DRAW);

}

DrawingusingVertexBuffersvoid DrawUsingVertexBuffers()voidDrawUsingVertexBuffers(){

glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,indexBuffer);glEnableClientState(GL_VERTEX_ARRAY);glVertexPointer(2, GL FLOAT, sizeof(vertexStruct),glVertexPointer(2,GL_FLOAT,sizeof(vertexStruct),(void*)offsetof(vertexStruct,position));glEnableClientState(GL_COLOR_ARRAY);lC l P i t (4 GL UNSIGNED BYTE i f( t St t)glColorPointer(4,GL_UNSIGNED_BYTE,sizeof(vertexStruct),(void*)offsetof(vertexStruct,color));

glDrawElements(GL_TRIANGLE_STRIP,g ( _ _sizeof(indices)/sizeof(GLubyte),GL_UNSIGNED_BYTE,(void*)0);

}}