2015春計(jì)算機(jī)圖形學(xué)空間信息introduction programming in opengl

1、1Programming in OpenGL中國(guó)地質(zhì)大學(xué)2History of OpenGLnSilicon Graphics (SGI) revolutionized the graphics workstation by implementing the pipeline in hardware (1982)nTo access the system, application programmers used a library called GLnWith GL, it was relatively simple to program three dimensional interact

2、ive applications 中國(guó)地質(zhì)大學(xué)3OpenGL: What is It?nThe success of GL lead to OpenGL (1992), a platform-independent API that was nEasy to usenClose enough to the hardware to get excellent performancenFocus on renderingnOmitted windowing and input to avoid window system dependencies 中國(guó)地質(zhì)大學(xué)4OpenGL: What is It

3、?nGL (Graphics Library): Library of 2-D, 3-D drawing primitives and operationsnAPI for 3-D hardware acceleration nGLU (GL Utilities): Miscellaneous functions dealing with camera set-up and higher-level shape descriptionsnGLUT (GL Utility Toolkit): Window-system independent toolkit with numerous util

4、ity functions, mostly dealing with user interface中國(guó)地質(zhì)大學(xué)5OpenGL ArchitectureDisplayListPolynomialEvaluatorPer VertexOperations &PrimitiveAssemblyRasterizationPer FragmentOperationsFrameBufferTextureMemoryCPUPixelOperations中國(guó)地質(zhì)大學(xué)6OpenGL as a RenderernGeometric primitivesnpoints, lines and polygons

5、nImage Primitivesnimages and bitmapsnseparate pipeline for images and geometryolinked through texture mappingnRendering depends on statencolors, materials, light sources, etc.中國(guó)地質(zhì)大學(xué)7OpenGL Geometric Primitives中國(guó)地質(zhì)大學(xué)8Specifying Geometric PrimitivesnPrimitives are specified usingglBegin(primType);.glE

6、nd();nprimType determines how vertices are combinedGLfloat red, green, blue;GLfloat x, y;glBegin(primType);for (i = 0; i nVerts; i+) glColor3f(red, green, blue); glVertex2f(x, y); . / change coord. valuesglEnd();中國(guó)地質(zhì)大學(xué)9OpenGL Vertex/Color Command FormatsglVertex3fv( v )Number ofcomponents2 - (x,y) 3

7、 - (x,y,z), (r,g,b)4 - (x,y,z,w), (r,g,b,a)Data Typeb - byteub - unsigned bytes - shortus - unsigned shorti - intui - unsigned intf - floatd - doubleVectoromit “v” forscalar form e.g.,glVertex2f(x, y)glColor3f(r, g, b)glColor3fv( v )中國(guó)地質(zhì)大學(xué)10Software OrganizationGLUTGLUGLGLX, AGLor WGLX, Win32, Mac O

8、/Ssoftware and/or hardwareapplication programOpenGL Motifwidget or similar中國(guó)地質(zhì)大學(xué)11Lack of Object OrientationnOpenGL is not object oriented so that there are multiple functions for a given logical functionnglVertex3f nglVertex2i nglVertex3dvnUnderlying storage mode is the samenEasy to create overload

9、ed functions in C+ but issue is efficiency中國(guó)地質(zhì)大學(xué)12OpenGL function formatglVertex3f(x,y,z)belongs to GL libraryfunction namex,y,z are floatsglVertex3fv(p)p is a pointer to an arraydimensions中國(guó)地質(zhì)大學(xué)OpenGLWindow management13n初始化（ glutInit ） glutInit function must be called before other function use glut

10、Init(&argc, argv);n設(shè)定窗口的顯示模式（ glutInitDisplayMode） glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); GLUT_DOUBLE, GLUT_INDEXnthe size and position of the window glutInitWindowPosition設(shè)置窗口在屏幕中的位置 glutInitWindowPosition(100,120) glutInitWindowSize設(shè)置窗口的大小 glutInitWindowSize(400,300)nCreate Window（ glutC

11、reateWindow） glutCreateWindow(矩形); glutMainLoop( )OpenGLWindow managementOpenGLWindow managementn指定窗口的顯示內(nèi)容函數(shù)（ glutDisplayFunc） glutDisplayFunc(Display)n運(yùn)行框架（ glutMainLoop） 啟動(dòng)主GLUT事件處理循環(huán)OpenGLGraphics rendering16n指定窗口背景色（ glClearColor）nglClearColor(1.0f, 1.0f, 1.0f, 1.0f);OpenGLGraphics rendering17混合

12、色紅色成分（R）綠色成分（G）藍(lán)色成分（B）黑0.00.00.0紅1.00.00.0綠0.01.00.0黃1.01.00.0藍(lán)0.00.01.0紫1.00.01.0青0.01.01.0深灰5淺灰0.750.750.75棕0.600.400.12南瓜橙0.980.6250.12粉紅0.980.040.70紫紅0.600.400.70白1.01.01.0OpenGLGraphics rendering18n刷新窗口的緩沖區(qū)（ glClear）n設(shè)定投影參數(shù) glMatrixMode(GL_PROJECTION); gluOrtho2D(0.0,200.0,0.0,150.0)

13、;n繪制圖形 glRectf(50.0f, 100.0f, 150.0f, 50.0f);OpenGL程序?qū)嵗?繪制矩形#include void Initial(void)glClearColor(1.0f, 1.0f, 1.0f, 1.0f); /設(shè)置窗口背景顏色為白色glMatrixMode(GL_PROJECTION); /設(shè)置投影參數(shù)gluOrtho2D(0.0,200.0,0.0,150.0);void Display(void)glClear(GL_COLOR_BUFFER_BIT); /用當(dāng)前背景色填充窗口glColor3f(1.0f, 0.0f, 0.0f); /設(shè)置當(dāng)前的繪

14、圖顏色為紅色glRectf(50.0f, 100.0f, 150.0f, 50.0f); /繪制一個(gè)矩形 glFlush(); /處理所有的OpenGL程序OpenGL程序?qū)嵗?繪制矩形int main(int argc, char* argv)glutInit(&argc, argv);glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); /初始化窗口的顯示模式glutInitWindowSize(400,300); /設(shè)置窗口的尺寸glutInitWindowPosition(100,120); /設(shè)置窗口的位置glutCreateWindow(

15、矩形); /創(chuàng)建一個(gè)名為矩形的窗口glutDisplayFunc(Display); /設(shè)置當(dāng)前窗口的顯示回調(diào)函數(shù)Initial(); /完成窗口初始化glutMainLoop(); /啟動(dòng)主GLUT事件處理循環(huán)return 0;OpenGL程序?qū)嵗?繪制奧運(yùn)五環(huán)#include GLuint OlympicRings;void Initial(void)glClearColor(1.0f, 1.0f, 1.0f, 1.0f); OlympicRings = glGenLists(1);glNewList(OlympicRings, GL_COMPILE);glColor3f(1.0, 1.0

16、, 0.0);glTranslatef(-22.0, 0.0, 0.0);glutSolidTorus(0.5, 20.0, 15, 50); /繪制黃色環(huán) glColor3f(0.0, 1.0, 0.0);glTranslatef(44.0, 0.0, 0.0);glutSolidTorus(0.5, 20.0, 15, 50); /繪制綠色環(huán)glColor3f(0.0, 0.0, 0.0);glTranslatef(-22.0, 30.0, 0.0);glutSolidTorus(0.5, 20.0, 15, 50); /繪制黑色環(huán)glColor3f(0.0, 0.0, 1.0);glTr

17、anslatef(-42.0, 0.0, 0.0);glutSolidTorus(0.5, 20.0, 15, 50); /繪制藍(lán)色環(huán)glColor3f(1.0, 0.0, 0.0);glTranslatef(84.0, 0.0, 0.0);glutSolidTorus(0.5, 20.0, 15, 50); /繪制紅色環(huán)glEndList();OpenGL程序?qū)嵗?繪制奧運(yùn)五環(huán)void ChangeSize(int w, int h)glViewport(0, 0, w, h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluOrtho2D (

18、-70.0f, 70.0f, -70.0f, 70.0f);OpenGL程序?qū)嵗?繪制奧運(yùn)五環(huán)void Display(void)glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW);glLoadIdentity();glCallList(OlympicRings); /調(diào)用顯示列表glFlush(); OpenGL程序?qū)嵗?繪制奧運(yùn)五環(huán)int main(int argc, char* argv)glutInit(&argc, argv);glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

19、 glutInitWindowSize(400,400); glutInitWindowPosition(100,100); glutCreateWindow(OpenGL模型繪制函數(shù)示例); glutDisplayFunc(Display);glutReshapeFunc(ChangeSize);Initial(); glutMainLoop(); return 0;OpenGL程序?qū)嵗?繪制奧運(yùn)五環(huán)Coordinate transformation sequence中國(guó)地質(zhì)大學(xué)26nOpenGL Matrix OperationsnGLU Clipping windownOpenGL Vi

20、ewport2d Viewing in OpenGL中國(guó)地質(zhì)大學(xué)27nglMatrixMode（GL_PROJECTION）nglLoadIdentity()；OpenGL Matrix Operations中國(guó)地質(zhì)大學(xué)28ngluOtho2D(xwmin, xwmax, ywmin, ywmax); Coordinate positions for the clipping window boundaries are given as double precision numbers.nThe default clipping window： wxl=-1.0，wxr=1.0， wyt=-1

21、.0， wyb=1.0GLU Clipping window中國(guó)地質(zhì)大學(xué)29nglViewPort（xvmin，yvmin，vpWidth，vpHeighht） All parameter values are given in integer screen coordinates relative to the display window.OpenGL Viewport中國(guó)地質(zhì)大學(xué)3031OpenGL CameranRight-handed systemnFrom point of view of camera looking out into scene:nOpenGL places a

22、 camera at the origin in object space pointing in the negative z directionnPositive rotations are counterclockwise around axis of rotation中國(guó)地質(zhì)大學(xué)32Coordinate SystemsnThe units in glVertex are determined by the application and are called object or problem coordinatesnThe viewing specifications are als

23、o in object coordinates and it is the size of the viewing volume that determines what will appear in the imagenInternally, OpenGL will convert to camera (eye) coordinates and later to screen coordinates中國(guó)地質(zhì)大學(xué)33Transformations in OpenGlnModeling transformationnRefer to the transformation of models (i

24、.e., the scenes, or objects)nViewing transformationnRefer to the transformation on the cameranProjection transformationnRefer to the transformation from scene to image中國(guó)地質(zhì)大學(xué)34Model/View TransformationsnModel-view transformations are usually visualized as a single entitynBefore applying modeling or v

25、iewing transformations, need to set glMatrixMode(GL_MODELVIEW)nModeling transforms the objectoTranslation:glTranslate(x,y,z)oScale: glScale(sx,sy,sz)oRotation: glRotate(theta, x,y,z)nViewing transfers the object into camera coordinates(定義觀察坐標(biāo)系)ogluLookAt (eyeX, eyeY, eyeZ, centerX, centerY, centerZ,

26、 upX, upY, upZ)中國(guó)地質(zhì)大學(xué)nViewing transfers the object into camera coordinates(定義觀察坐標(biāo)系)ogluLookAt (eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ)oP0（ eyeX, eyeY, eyeZ ）觀察坐標(biāo)系原點(diǎn)oPref（ , centerX, centerY, centerZ ）reference positiono upX, upY, upZ 定義觀察正向矢量Model/View Transformations中國(guó)地質(zhì)大學(xué)3536Mo

27、del/View transformationCourtesy: Neider, Davis and Woo, “The OpenGL Programming Guide”中國(guó)地質(zhì)大學(xué)37Projection TransformationnTransformation of the 3D scene into the 2D rendered image planenBefore applying projection transformations, need to setglMatrixMode(GL_PROJECTION)nOrthographic projectionoglOrtho(l

28、eft, right, bottom, top, near, far)nPerspective projectionoglFrustum (left, right, bottom, top, near, far)中國(guó)地質(zhì)大學(xué)38Projection TransformationF.S.Hill, “Computer Graphics using OpenGL”O(jiān)rthographic projectionPerspective projection中國(guó)地質(zhì)大學(xué)nvoid gluPerspective (GLdouble fovy, GLdouble aspect, GLdouble zNear

29、, GLdouble zFar);OpenGL symmetric perspective projection function.Projection Transformation中國(guó)地質(zhì)大學(xué)3940GLUT event loopnLast line in main.c for a program using GLUT is the infinite event loopglutMainLoop();nIn each pass through the event loop, GLUT nlooks at the events in the queuenfor each event in th

30、e queue, GLUT executes the appropriate callback function if one is definednif no callback is defined for the event, the event is ignorednIn glutDisplayFunc(mydisplay) identifies the function to be executednEvery GLUT program must have a display callback中國(guó)地質(zhì)大學(xué)41Posting redisplaysnMany events may invoke the display callback functionnCan lead to multiple executions of the display callback on a single pass through the event loopnWe can avoid this problem by instead usingglutPostRedisplay(); which sets a flag. nGLUT checks to see if the flag is set at the e