Texture mapping is one of the techniques in computer

graphics for image processing applications. It has been

used to add realism to computer graphics, images were rendered

became more interesting. This technique made a simple

image looks closer to the original object in real life. In

this paper, we explain about how to apply texture mapping

technique using OpenGL library and also applying texture

mapping in solar system simulation using Microsoft Visual

Basic language supported with OpenGL library. Open GL

was made by Saadat Ali Shah, using OpenGL library which

is known as an open source software that compatible to any

programming applications

Junatas, Bismar

Valentine, Vega

W., Eri Prasetyo

Gunadarma University Repository

WOSOC 2008 - Workshop on Open Source and Open Content, 1-3 December 2008, Bali - Indonesia137Texture Mapping for Solar System Simulation(OpenGL Implementation)Eri Prasetyo W.Gunadarma UniversityJl. Margonda Raya 100 DepokIndonesiaeri@staff.gunadarma.ac.idBismar JunatasBachelor Master Degree ProgramGunadarma UniversityIndonesialepen 72@student.gunadarma.ac.idVega ValentineBachelor Master Degree ProgramGunadarma UniversityIndonesiaslaved jepun@student.gunadarma.ac.idAbstractTexture mapping is one of the techniques in computergraphics for image processing applications. It has beenused to add realism to computer graphics, images were ren-dered became more interesting. This technique made a sim-ple image looks closer to the original object in real life. Inthis paper, we explain about how to apply texture mappingtechnique using OpenGL library and also applying texturemapping in solar system simulation using Microsoft VisualBasic language supported with OpenGL library. Open GLwas made by Saadat Ali Shah, using OpenGL library whichis known as an open source software that compatible to anyprogramming applications.Keywords:Texture Mapping, Computer Graphics,SolarSystem, Simulation, Open GL.1 Introduction1.1 Texture MappingTexture mapping is a method for adding detail, sur-face textures, or colors to a computer-generated graphics or3D models. This technique basically patching a texture im-age onto an object, usually applied to a surface of a shapeor polygon [3].Generally, mapping a texture requires these steps [4]:1. Create a Texture Object and Specify a Texture for ThatObjectA texture is usually thought of as being two-dimensional, like most images, but it can also be one-dimensional or three-dimensional. The data describ-ing a texture may consist of one, two, three, or fourelements per texel and may represent an R, G, B or Aquadruple, a modulation constant, or a depth compo-nent.2. Indicate How the Texture Is to Be Applied to EachPixelWhen mapping an image onto an object, the color ofthe object at each pixel is modified by a correspond-ing color from the image. There are several func-tions to compute the final RGBA value from the frag-ment(object) color and the texture image data.One of those functions called Replace Mode. It usesthe texture color as the final color, in which the textureis painted on top of the fragment.Another method is using the texture to modulate orscale, the fragment’s color. This technique is usefulfor combining the effects of lighting with texturing.Finally, a constant color can be blended with that onthe fragment, based on the texture value.3. Enable Texture MappingYou need to enable texturing before drawing yourscene.4. Draw the Scene, Supplying Both Texture and Geomet-ric CoordinatesWe need to indicate how the texture should be alignedrelative to the fragments it is being applied before thetexture glued on. That is, we need to specify bothtexture coordinates and geometric coordinates as youspecify the objects in your scene.WOSOC 2008 - Workshop on Open Source and Open Content, 1-3 December 2008, Bali - Indonesia1381.2 Solar System SimulationSolar system consists of sun, planets, and moons.Solar system simulation gave us some information aboutthe orbit of planets and moons, and of course the sun [2].To run this simulation, an adequate knowledge dealing withthe solar system modelling is required. It is related with co-ordinate determination, object movements, and object for-mation. Solar system modelling deals with:1. MappingIn computer graphics, mapping method has a lot offunctions. Basically, mapping is used to make a modellook closer to the real image by adding some texture.Texture mapping is just one kind of the basic mappingmethod(further about texture mapping has been dis-cussed in section 1). Other kinds of mapping methodsare Bump mapping, Normal mapping, Parallax map-ping or Offset Mapping, and Displacement mapping.2. Bresenham’s AlgorithmBresenham’s line algorithm is an algorithm that deter-mines which points in an n-dimensional raster shouldbe plotted in order to form a close approximation toa straight line between two given points. Bresenham’salgorithm was one of the earliest algorithms which wasdeveloped in the field of computer graphics.3. Transformation MatrixTransformation matrix is a matrix changing by an alge-bra function. In this paper, transformation matrix wasused to rotating, translating and scaling.Transformation matrix was used in computer graphicsoftentimes and furthermore was used in modelling an-imation.2 Application Design in OpenGL2.1 Texture Mapping with OpenGLOpenGL(Open Graphics Library) is a spesificationstandard which defines an API platform language for mak-ing an application resulting 2D and 3D computer graphics.Its interface consists of more than 250 different functionswhich allows it to draw complex 3D scenes, from the sim-plest and easy scene to a more complicated one.OpenGL is developed by Silicon Graphics Inc.(SGI) in1992. It is a popular application in video game industrywhich is a competitor of Direct3D application developedby Microsoft Windows. OpenGL development has raised toa CAD, Virtual Reality, knowledge visualization, informat-ics visualization, flight simulation, and video game devel-opment.Solar system simulation needed certain techniques. Oneof the techniques is texture mapping which needed toadding realism to the simulation. OpenGL currently has thestatements allowing texture mapping functions, such as:1. glBindTexture()glBindTexture statement form the geometric objecttexture.2. GL TEXTURE 1D,GL TEXTURE 2D,GLTEXTURE 3D,and GL TEXTURE CUBE MAPGL TEXTURE works as the texture parameter desti-nation from the geometric object. It is also a symbolicconstant which usually follow the statement glEnable()or glDisable(). These two statements is to activate ordeactivate texturing in geometric objects.3. gluSphere QObj, x, y, zThis statement is to make a spherical object as a ballwith x, y, and z parameters so that the object become3D. gluSphere draws a sphere of the given radius cen-tered around the origin. The sphere is subdividedaround the z axis into slices and along the z axis intostacks(similar to lines of longitude and latitude).4. glTexParameteriThis statement determines the parameters used in thetexture. Used as the integer texture with two parame-ters, magnification and minification.2.2 Solar System Simulation with OpenGL• First, loading a picture into the program• Second, after the image loaded, displaying the imageusing the code below:1. glColor3f 1, 0.6, 0 is a OpenGL statement to dis-play colors in an object, on the listing above, thisstatement is to give colors to the sun, 1 for red,0.6 for green, and 0 for blue.2. glRotatef Rt, 0, 1, 0 Rt, 0, 1, 0 to rotate the sun.Rt in the statement above means rotation done inRt0 value in a clockwise direction. The second,third, and fourth parameters define the rotationfuse, which is the x, y, and z axis. If the thirdparameter value is 1, it means the rotation donein y axis.3. gluSphere QObj, 3, 20, 20 used to display sunas a sphere which has the value 3 for diame-ter, has 20 slices adn 20 stacks, and also callthe QObj function which is used to give texturein gluQuadric mode with true value and normalwith smooth value.WOSOC 2008 - Workshop on Open Source and Open Content, 1-3 December 2008, Bali - Indonesia1394. In the listing above, there are no statement tocontrol the migration of the sun because the sundoesnt do any revolution. Unlike the sun, planetsare doing revolution of the sun in a certain or-bits. In order to enable the planets move alongits orbit in this simulation, there are the state-ment glTranslatef 10!, 0!, 0!.. This statement isto make a translation of an object with 10 posi-tion for x axis, and 0 for both y and z axis.• Third, display the sun flare if user chooses sun in thecombobox using the code below:1. glEnable GL BLEND is used to unite two ob-jects. In this program, GL BLEND used to unite2D texture with the texture owned by sun andplanets. To deactivate GL BLEND mode, usegldisable GL BLEND.2. glColor4fv SunClr(0) used to display SunClr(0)color consist of four components. Each compo-nent reached by calling the SunClr function.3. glPushMatrix used to temporarily store all state-ments between glPushMatrix and glPopMatrixinto a stack. glPopMatrix used to pop statementsin the stack.4. glRotatef -25, 1, 0, 0 dan glRotatef Rt, 0, 0, 1used to rotate the sun. -25 and Rt means rotationdone in a clockwise direction in 25o value. Thesecond, third, and fourth parameters denote therotation fuse which is x, y, and z axis.3 Solar System Simulation in MS Visual Ba-sic (OpenGL Library)In this section we will explain about Solar Systemsimulation program which made with Visual Basic 6.0 (us-ing OpenGL library). OpenGL library has been explainedin the second section of this paper.This program consist of three modules, two forms, and aclass module. First we will examine the module which theprogram have. This program has three modules,i.e. :1. Hook ModuleThis module works to configure program view if thewindows size of this program has changed. This Mod-ule comprises three parts, first is declaration of thevariables which are used, second is hook and unhookfunction, and last is windows proc. function. HookFunction contains statement which works to begin sub-classing which call by the main program. Unhookfunction is the opposite of hook function,which is thisfunction to stop the module. Windows proc. functionis a function which call by hook function at this mod-ule. This function defines the size of solar system in-formation program windows.2. OGL ModuleThis Module works when the program loads picture attime the program runs. Besides, this module managesall of the property it has.3. XP ModuleThis Module works to give XP Style to the exe pro-gram. XP module function is not giving big contribu-tion to the main program.Hereafter we will introduce all forms available on thisprogram. This program has two forms, i.e. :1. Main FormThis form performs the solar system simulation.TheForm also manage the speed of planet revolution to thesun.2. Form AboutThis form has explanation and information about theprogrammer. The form only appears when user callthat form with command button a¨bout” from the mainform.The program will appear as shown below:Figure 1. Solar System Simulation ProgramThis program has a feature to change the Sun flare color,it is the ¨Sun Flare Color c¨ombo box.This application also has VB timer class module.VB timer module giving FPS and Rt3 value which usedin floating camera. ¨Floating Camera c¨heck box changethe camera view by changing Rt3 value, so when sub ren-der glview1 called to display sun and planets, Rt3 valuebeing used is the new Rt3 value, so the camera view ischanged.WOSOC 2008 - Workshop on Open Source and Open Content, 1-3 December 2008, Bali - Indonesia140The program also giving choices whether the user wantsto see orbit lines or not. The choices determined by ¨ShowPlanet Path c¨heck box.4 ConclusionSolar system simulation was made by computergraphics, using some texture mapping techniques to havemore realistic simulation.In this paper, we explain a program, made by Saadat AliShah [1], using OpenGL library which is known as an opensource software that compatible to any programming appli-cations. OpenGL is one of the most common library used incomputer graphics. This application was made by integrat-ing OpenGL library onto Microsoft Visual Basic. By usingfunctions provided in OpenGL and Microsoft Visual Basic,texture mapping can be applied to the simulation and forma realistic and natural simulation.This application hopefully can help us to understand so-lar system dan of course about computer graphics theory(inthis case texture mapping).In the future, we can enhance this application. Maybeby making the window size more flexible because we stillhave problem with its static size. Besides, this program stillhave a bug. If we click on the sun, planets, or other partsof the simulation, the program will terminate automatically.Hopefully on the future, we can fix this problems to makean optimum application of solar system simulation.References[1] http://www.programmersheaven.com.[2] Adrifina and Wisnu Maulana. Solar System SimulationUsing OpenGL. Technical report, Gunadarma Univer-sity, 2007.[3] Paul & Mark Segal Haeberli. Texture Mapping as aFundamental Drawing Primitive. 1993.[4] Shreiner. Texture Mapping. 2005.

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