OpenGL Graphics Through Applications

334 Pages·2008·6.649 MB·English

by  Robert Whitrow

Robert Whitrow
OpenGL Graphics
Through Applications
RobertWhitrowBSc,PhD
LondonMetropolitanUniversity,UK
ISBN:978-1-84800-022-3 e-ISBN:978-1-84800-023-0
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Preface
This book is the result of teaching computer graphics for one and two semester,
yeartwo/threeundergraduateandpostgraduatelecturecoursesinComputerGraph-
ics.Throughoutthebook,theoryisfollowedbyimplementationusingC/C++and
complete programs are provided with suggestions for change to enhance student
understanding.During30yearsofuniversityteachingtheauthorhasbecomeaware
of the frustration that many students suffer, of code fragments that ‘never quite
work’andprogramsthatonadifferentsystemrequiresystemdependentadditions!
Withthisinmindalltheprograms given have been testedusingMSC++ v6 and
mosthavebeentestedusingSolaris4.2andBorlandC++v5.
ThereareanumberoftextswhichgiveamoreindepthapproachtotheOpenGL
pipelineandrepetitionhasthereforebeenavoidedbyreferencingsuchtextsforthe
interestedreader.Theobjectiveistogetstudentsimmersedingraphicsapplications
as rapidly as possible, to develop confidence, which in turn leads to experimenta-
tion, which is so vital to the enthusiastic programmer. Theory and practice have
beendevelopedinparallelsothatinmanycasesthereaderbeginstounderstandthe
strengthsandweaknessesofaparticularalgorithm.
After a rapid ‘getting started’ introduction we look at the structure of bit map
(.bmp)filesasaprecursortounderstandingaudiovisualfiles(.avi).Thisworkforms
a foundation for later sections on image processing and texturing. These are very
simple file structures that can be converted from other image file formats using
commerciallyavailablesoftwarepackages.Thechapterintroducingimageprocess-
ingcoversedgedetection,enhancementanddatacapturefromCATscans.Theory
andpracticecanbequitedifferentandsomeprocessingappearsmoreofanartthana
scienceduetothevariabilityintheimagequalityandthenatureoftheimageitself.
The example of edge finding on CAT scans where different slices may have well
definededgesandothermorefuzzyedgesduetograyhairisnotalwaysapparentto
theeye.Weaddresstheseproblemswithalternativesolutionswithvaryingdegrees
ofsuccesstoenablereaderstocomprehendthatalgorithmicdevelopmentisstillan
inexactscienceforsuchapplications.
InChapter4wemovetothefirstchapter,whichmightbeconsideredtobecom-
putergraphicswithallthemathematicsthatisrequired.Idonotencouragestudents
toskipovertheseareasofunderstandingforthe‘blackbox’approachwillonlyget
yousofarandgapsinknowledgeatanearlystagewillcometohauntonelateron.
The toil of getting to grips with material will be amply repaid as students grow in
knowledge–althoughIamawarethatmanyavoidthejoysofmathematicalrigor!
v
vi Preface
Early on in computer graphics students are often heard to say; “why is there
noerrormessageandnothingonthescreen?”.Knowingwhereoneisin3Dspace
has been another difficult area to communicate. Conceptually compressing a 3D
modelontoa2Dscreendoesnotcomeeasilytomanystudents’mindsandherewe
introduce viewing. In OpenGL the viewing process is concerned with two opera-
tions;themappinganobjectintoaviewingvolumeforscreendisplayandcalledthe
PROJECTION process, while the orientation and size operations on the object is
referredtoastheMODELVIEWprocess.Beinginthewrongplace,whetherviewer
or object can leave nothing on a screen and much confusion as how to proceed.
The author maintains that there is little alternative to debugging than printing out
a few well-chosen coordinates to see if they lie in the field of view! With practice
onebecomesawareoflocation,butintheearlystages3Dspaceseemslikelearning
toflyincloud–fewreferencepointsandadegreeofpanicifyoudon’ttrustyour
instruments(coordinatevaluesinourcase).
Lightingbeginstobringrealismtodisplaysandinthissectionwecoverthedif-
ferentformsoflightingavailableandseetheeffectsaswemoveobjectsinrelation
toalightsource.Wealsolinktheearlyworkonthetransformationsasweseehow
illumination varies across a surface and adjust the surface properties to produce
highlights.
In Chapter 7 we return to bit map images and use them to cover surfaces with
pictures,initiallyonsimpleflatplanesandthendeveloplinearmappingmethodsfor
more complex surfaces. We introduce the concept of mapping onto terrain with a
givenheightprofiletosimulatetheideaofmountainsandvalleys.Multipletextures
are used to simulate scenery as seen through windows and the changes apparent
from movement in a room are implemented. An introduction to 3D texturing is
includedandfinallyreconstructionof3Dvolumesfrom2DCATscanslices.
Object orientation has played a lesser part in the text up to this section and
we now use the concept to build artifacts based on work in the previous chapters.
Objects such as cylinders and ‘stretched cubes’ are textured with an appropriate
image and result in building blocks for furniture. The tables built are then placed
within the context of say a room to introduce students to applications of furniture
androomdecoration.Thewritingratherthanonlyusingobjectshasprovedfruitful
in student projects, where an understanding of mass manufacture has led students
to consider in some depth the flexibility required in design for object use to be
economic.
ThefinalchapterconsidersthedevelopmentofcurvesandsurfacesusingSplines
and Bezier interpolation and fractals. A section on fractals explores the role they
canplayinaddingobjectstosceneryandoutliningcomplexshapes.
Approach
Thisbooksetsouttosolveproblemsbycompleteexampleratherthandiscursively
hintofhowitmaybedone.Weliveinaneraofmasseducationwhereasever,the
veryablethrivewithoutmuchneedofteachingbutwherethelargemassofstudents
Preface vii
have less access to staff due to funding constraints. Some believe technology will
overcometheseobstaclesandtheauthorbelievesthatonecontributiontothesolu-
tion of the problem is doing by example. However, a black box recipe approach
leaves students vulnerable when circumstances change and thus I have included
theory followed by worked examples. The initial implementation sometimes pro-
duces inefficient code and I have left this deliberately in order that students can
followwherealgorithmsoriginatefromtheory.Goodprogramdesignandefficient
code comes from an in depth understanding that is the result of a long process of
assimilation.
SupportingMaterial
SupportmaterialsmaybefoundmaybefoundontheaccompanyingSpringerweb
sitehttp://www.springer.com/978-1-84800-022-3
Theyinclude:
Programcode
Datafiles
OpenGLincludefiles
OpenGLlinklibrariesfromtheMesasite.
RobertWhitrow
DepartmentofComputing
CommunicationsTechnologyandMathematics
LondonMetropolitanUniversity,UK
Acknowledgements
The enthusiasm of my students has made a major contribution to making this
text possible. I would particularly thank George Fordham, A Saadat, Paul Kunka,
AbidKhan,MichelleStafford,CecilleBoulanger,PaulArmstrongandmanyothers
whose names escape me now who I learnt from and who inspired me with their
enquiringmindsandneverendingquestions.Theirworkandeffortsarepartofthis
book and without out meeting first hand the problems of learning, I would have
neverbeendriventowritethistext.
As with any course, material develops over time and occasionally the original
sourcecanbeeasilyforgotten.InthistextIhavereferencedsourcesthathavebeen
particularly helpful in my teaching, developing this text and will be valuable to
readerswhowishtoexplorefurtherassupportingmaterial.
I would also thank Dr Ronnie Burton who first welcomed me to his OpenGL
courseintheautumnof2001andwithhisencouragementsuggestedItakeateach-
ingroleinthepresentationatLondonMetropolitanUniversity.Ronnieunstintingly
gave of his time and knowledge, which made this work possible. I cannot let pass
the support of Professor Jim Yip and Professor Ian Haines who appointed me and
providedthetimeandspacetocompletethetext.Theirenthusiasm,encouragement
andleadershipwasanexampletoall–thankyou.
Aswithmanytasksthereisoftenafrequentlyhiddenunseensupportintheback-
ground – my wife Despoulla who has cajouled and pressed for completion when
I could find reasons for vaccilation! I recognise and thank her for the persistent
determinationthatwasamajorcontributiontothesuccessofthework.
Theprimarypurposeofeducationistomakeone’smindapleasantplaceinwhichtospend
one’sleisure–S.J.Harris
ix
Contents
1 GettingStarted ................................................. 1
1.1 Introduction................................................ 1
1.2 AccesstoLibraries.......................................... 2
1.3 DataTypes ................................................ 2
1.4 Terminology ............................................... 3
1.5 TheOpenGLUtilityToolkit–GLUT ........................... 3
1.6 OurFirstProgram........................................... 4
1.6.1 DrawingPrimitives .................................. 7
1.6.2 Gaps,LinesandBlobs ............................... 10
1.6.3 OtherLineTypes.................................... 11
1.6.4 SurfacePatternsandPolygonStippling ................. 12
1.6.5 CharacterGeneration ................................ 15
1.7 ParametricRepresentationofCurves........................... 17
1.7.1 TheGrowthorLogarithmicSpiral...................... 19
1.8 ApproximationandProcessingEfficiency....................... 21
1.8.1 LineDrawing....................................... 22
1.8.2 TheDigitalDifferenceAnalyser ....................... 23
1.8.3 Bresenham’sAlgorithm .............................. 25
1.8.4 Bresenham’sAlgorithmforaCircle .................... 27
1.9 ProblemSolvingThroughGraphics............................ 31
1.10TheApplicationProgrammingInterface(API)................... 34
1.10.1 TheOpenGLUtilityToolkit(GLUT)Library ............ 34
1.10.2 MouseInteraction ................................... 35
1.10.3 KeyboardInteraction................................. 36
1.11Exercises .................................................. 37
1.12Conclusion ................................................ 37
2 ImageFileFormats.............................................. 39
2.1 Introduction................................................ 39
2.2 TheBitmapFile ............................................ 39
2.2.1 Bitmap-fileStructure................................. 40
2.2.2 ATypicalFileLayout ................................ 41
xi
xii Contents
2.2.3 ReadingandDrawingaBitmapFile .................... 42
2.2.4 CreatingaDisplayWindow ........................... 45
2.2.5 CreatingtheImageforDisplay ........................ 46
2.2.6 MonochromeBitmaps................................ 46
2.2.7 AGeneralClassforInputofBit
MapFiles ......................................... 47
2.2.8 ManipulatingBitMaps–Embossing ................... 49
2.3 Audio/VideoInterleaved(AVI)FileFormat ..................... 51
2.3.1 ChunkHierarchy .................................... 53
2.3.2 AnExampleofWebCamDisplay...................... 55
2.3.3 Compression ....................................... 58
2.4 Exercises .................................................. 59
2.5 Conclusion ................................................ 59
3 ImageProcessing................................................ 61
3.1 Introduction................................................ 61
3.2 FindingObjects ............................................ 61
3.2.1 EdgeDetection...................................... 62
3.2.2 NumericalImplementation............................ 63
3.2.3 SobelOperator...................................... 63
3.2.4 Convolution ........................................ 64
3.2.5 LaplacianOperator .................................. 66
3.2.6 SmoothingandEdgeFinding.......................... 69
3.3 HistogramEqualisation ...................................... 71
3.4 Component(object)Labelling ................................ 73
3.4.1 ExploringConnectivity(1)............................ 74
3.4.2 ExploringConnectivity(2)............................ 76
3.4.3 MultipleRegions.................................... 77
3.5 DrawingontheScreenandDataCapture ....................... 77
3.5.1 OutliningofAreasofInterestonImages ................ 80
3.5.2 AnApproachtoAutomatingEdgeDetection............. 82
3.6 Exercises .................................................. 85
3.7 Conclusion ................................................ 85
4 Transformations ................................................ 87
4.1 Introduction................................................ 87
4.2 RepresentingPointsandVectors............................... 87
4.2.1 VectorDotProducts ................................. 89
4.2.2 TheVectorCrossProduct............................. 89
4.2.3 UsingtheCrossProducttoProvideColourVariation
toaCylinder....................................... 91
4.3 CoordinateSystems ......................................... 94
4.4 Transformations ............................................ 95
4.4.1 Rotation ........................................... 96
4.4.2 ASimpleExampleofRotation ........................ 98
Contents xiii
4.4.3 GeneralRotationsAboutAnyPoint .................... 99
4.5 TheModelViewMatrix .....................................103
4.6 AddingSomeMovement.....................................103
4.6.1 MovementofCompositeObjects.......................104
4.6.2 TheOrrery .........................................104
4.6.3 TheInternalCombustionEngine.......................107
4.6.4 Arms,Robots,ActuatorsandMovement ................113
4.6.5 DataCaptureofLimbMovement ......................114
4.6.6 Animation–AWalkingRobot.........................116
4.7 CollisionDetection .........................................120
4.8 Exercises ..................................................124
4.9 Conclusion ................................................124
5 ViewingandProjection ..........................................125
5.1 Introduction................................................125
5.2 VertexPipeline .............................................125
5.3 TheViewingProcess ........................................126
5.3.1 EngineeringDrawings................................128
5.4 OrthographicorParallelProjection ............................132
5.4.1 FromRealWorldtoScreenWindow....................132
5.4.2 InsidetheMatrix ....................................134
5.4.3 GettingtoGripswithWhereThingsAre ................137
5.4.4 PerspectiveProjection................................139
5.4.5 UnderstandingtheView ..............................143
5.5 Exercises ..................................................145
5.6 Conclusion ................................................146
6 LightingandColour.............................................147
6.1 Introduction................................................147
6.2 TheElectromagneticSpectrum................................147
6.2.1 Colour.............................................148
6.2.2 MixingColours .....................................149
6.2.3 TheShadingModel..................................150
6.3 LightingandIllumination ....................................151
6.3.1 SettinguptheLighting ...............................152
6.3.2 AdditionofSpecularLight............................157
6.4 ASyntheticFace ...........................................162
6.4.1 GettingtheVertexCoordinates ........................162
6.4.2 MovingtheEyeandLightSourceTogether..............163
6.5 Shadows–AProjection......................................164
6.5.1 DerivationoftheShadowOutlineUsingEquation
ofaLine ..........................................164
6.5.2 APolygonMovingShadow ...........................166
6.6 Exercises ..................................................168
6.7 Conclusion ................................................169
xiv Contents
7 TextureMapping................................................171
7.1 Introduction................................................171
7.2 TheMappingProcess........................................171
7.3 SettingupTextures..........................................172
7.3.1 DrawingtheTexture .................................174
7.4 MappingontoCurvedSurfaces................................176
7.4.1 MercatorLinesofProjection ..........................176
7.4.2 QuadricSurfaces ....................................177
7.4.3 MappingontoaSphericalSurface......................178
7.4.4 MappingoneImagetoSphere .........................182
7.4.5 CylinderTexturingMapping ..........................184
7.4.6 MappingtoaCircle..................................185
7.4.7 MappingtoaCone ..................................186
7.4.8 MappingontoaGeneralSurface .......................189
7.4.9 MappingontoaContourSurface.......................191
7.5 AddingSomeMovement–ARotatingHemisphere ..............193
7.5.1 MovementviatheMouse .............................196
7.6 UsingBitMapstoProvideContext ............................200
7.6.1 Blending...........................................202
7.6.2 ManipulatingPixels..................................206
7.7 Three-DimensionalTexturing.................................212
7.7.1 SimulationofaSphericalObject.......................213
7.7.2 BuildingaSolidModelofaHead ......................219
7.8 Exercises ..................................................226
7.9 Conclusion ................................................226
8 ObjectstoArtefacts .............................................227
8.1 Introduction................................................227
8.2 ArtefactHierarchy ..........................................227
8.2.1 ConstructionDoubleSidedSquares ....................228
8.2.2 ABoxasaBasicBuildingBlock ......................232
8.2.3 BuildingaTable.....................................233
8.3 IntegratingtoaSystem ......................................235
8.4 ChangingtheFurnitureStyle .................................243
8.5 Exercises ..................................................247
8.6 Conclusion ................................................247
9 Curves,SurfacesandPatterns ....................................249
9.1 Introduction................................................249
9.2 FittingaLineoraCurve .....................................250
9.2.1 StraightLineFittingtoDataPoints.....................250
9.2.2 LagrangePolynomialsandCurveFitting ................251
9.2.3 APracticalApproachtoCurveFitting ..................251
9.2.4 CurveFittingUsingCubicSplines .....................252
9.2.5 SurfaceConstructionfromContourMaps ...............256