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Understanding of OpenGL

Understanding of OpenGL. Transformations and Projections. TA: Dong Hyun Jeong Instructor : Dr. Kalpathi Subramanian. Purpose. Short overview of OpenGL Understanding of basic knowledge about OpenGL Short discussion on how to use OpenGL including transformations and projections.

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Understanding of OpenGL

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  1. Understanding of OpenGL Transformations and Projections TA: Dong Hyun JeongInstructor : Dr. Kalpathi Subramanian

  2. Purpose • Short overview of OpenGL • Understanding of basic knowledge about OpenGL • Short discussion on how to use OpenGL including transformations and projections

  3. What is OpenGL? • Software Interface for 3D Graphic Hardware (Instruction sets) • Interactive 2D and 3D graphics application programming interface (API) • Support high visual quality and performance • CAD/CAM, entertainment, medical imaging, virtual reality, Etc. • Developer-driven advantages • Industry standard, stable, reliable and portable, easy to use ……

  4. Supports • Operating systems • Mac OS, OS/2, UNIX, Windows 95/98, NT, 2000, Linux, OPENStep, BeOS • Windowing systems • Win32, MacOS, Presentation Manager, X-Window System • Callable from • C, C++, Ada, Fortran, Python, Perl, Java

  5. Flexibility and Extensions • Has flexibility of defining a particular OpenGL implementation depending on systems • OpenGL has extensions (API) • GLU, GLX, WGL (defined by vendors) UNIX APPLICATION WINDOWS APPLICATION GLU GLU Xlib GLX OpenGL GDU WGL OpenGL • OpenGL applications use the window system’s window, input, and event mechanism • GLU supports quadrics (2D curve), NURBS, complex polygons, matrix utilities, and more

  6. Several Advanced API • Open Inventor • Supports cross-platform user interface and flexible scene graph • IRIS Performer • Visual simulation and virtual sets (demanding high frame rate) • OpenGL Optimizer • Real-time interaction, modification, and rendering of complex surface-based models (CAD/CAM, special effects)

  7. Several Advanced API • OpenGL Volumizer • High-level immediate mode volume rendering API (energy, medical and sciences) • OpenGL Shader • Realistic visual effects, bump mapping, multiple textures, etc.

  8. Vectorize Clip Transform To viewport Draw Viewport and Viewport Clipping • Projecting 3D objects onto 2D screen (CG process pipeline) • Viewport • A two-dimensional (2D) rectangle into which a 3D scene is projected • Vecterize • Representing 3D objects as line or plane pieces of objects or elements • Clipping (Clip) • Remove the not interested regions from the vecterized elements

  9. Viewport and Viewport Clipping • Clipping Volume • Physical coordinate or Global coordinate to represent the 3D objects. glOrtho(), gluPerspective() • Viewport • Plane regions to map the physical coordinate into windows’ pixel coordinate. glViewport() • Viewing transform • Changing user’s viewing angle to represent the 3d objects. glTranslated(), glRoated(), glMatrixMode(), gluLookAt()

  10. Displaying Objects

  11. Drawing a triangle on screen • Clear the screen • Create a triangle • Determine the location and direction of the triangle • Change the viewing angle • Define a projection method

  12. Clear the screen • Remove the frame buffer • glClearColor(0.0,0.0,0.0,0.0); • glClear(GL_COLOR_BUFFER_BIT);

  13. Create a triangle • A triangle as a geometry object void DrawTriangle() { glColor3f(1.0f,0.0f,0.0f); glBegin(GL_TRIANGLES); glVertex3f(0.0f,0.0f,0.0f); glVertex3f(1.0f,0.0f,0.0f); glVertex3f(0.0f,1.0f,0.0f); glEnd(); }

  14. Y Rotate Translate X Z Positioning • Determine the location and direction of the triangle • glTranslatef(1.0f,1.0f,0.0f); • glRotatef(45.0f,0.0f,1.0f,0.0f); • DrawTriangle();

  15. Y X Z Viewing angle • Change the viewing angle • glMatrixMode(GL_PROJECTION); • glLoadIdentity(); • glOrtho(-1.0f,1.0f,-1.0f,1.0f,-1.0f,10.0f); • glMatrixMode(GL_MODELVIEW); • gluLookAt(1.5f,1.5f,1.0f,1.5f,1.5f,-0.5f, 0.0f,1.0f,0.0f);

  16. Y X Z Projection • Determine the projection • Perspective Projection • glFrustum(-1.0f,1.0f,-1.0f,1.0f,1.0f,100.0f); • Orthographic Projection • glOrtho(-1.0f,1.0f,-1.0f,1.0f,0.0f,100.0f); Perspective Projection Orthographic Projection

  17. v4 v4 v0 v5 v0 v3 v3 v1 v2 v1 v2 v4 v0 v5 v3 v1 v2 v4 v0 v5 v3 v1 v2 v5 v4 v4 v0 v0 v0 v5 v2 v3 v4 v3 v1 v1 v1 v2 v3 v2 v5 Geometry elements I • Points • GL_POINTS • Lines • GL_LINES, GL_LINE_STRIP, GL_LINE_LOOP • Triangles • GL_TRIANGLES, GL_TRIANGLES_STRIP, GL_TRIANGLE_FAN

  18. v5 v3 v7 v6 v4 v0 v3 v6 v5 v0 v1 v7 v2 v1 v4 v2 v2 v1 v3 v0 v5 v4 Geometry elements II • Quadric • GL_QUADS, GL_QUAD_STRIP • Polygon • GL_POLYGON

  19. Valid Invalid Basic restrictions • All have to be plane objects • No halls • Edges do not have to be crossing

  20. Creating complex objects • Complex objects using connected lines • Complex objects using connected triangles

  21. Vertex transformation

  22. Viewing • Positioning a object • Change the viewing angle • Projection and transformation • Viewport and coordinate determination

  23. Rotate Modeling Transformation • Place object and change the viewing angle • glMatrixMode(GL_MODELVIEW) • glLoadIdentity() – Identify matrix is called • glTranslatef(x,y,z) • glRotatef(degree,x,y,z) • glScalef(x,y,z) Translate Scale

  24. Viewing Transformation • Changes the position and orientation of the viewpoint • Generally it consists of translations and rotations. • gluLookAt()

  25. Projection Transformations • Defining a viewing volume • determines how an object is projected onto the screen • glMatrixMode(GL_PROJECTION); • glLoadIdentity(); • glFrustum(left,right, bottom,top, near, far); • glOrtho(left,right, bottom,top, near, far);

  26. Perspective Projection I • glFrustum(left, right, bottom, top, near, far); • (left, right, bottom, top) - near clipping plane • nearand far give the distances from the viewpoint to the near and far clipping planes. • Easy to understand, but not intuitive to use

  27. Perspective Projection II • gluPerspective(fovy, aspect, near, far); • Creates a matrix for a symmetric perspective-view frustum

  28. Orthographic Projection • the viewing volume is a rectangular parallelepiped • glOrtho(left, right, bottom, top, near, far);

  29. Viewport Transformation • The viewport is the rectangular region ofthe window where the image is drawn • Measured in window coordinates, which reflect the position of pixels on the screen relative to the lower left corner of the window. • glViewport(x, y, width, height);

  30. Aspect Ratio • Mapping the Viewing Volume to the Viewport • Displayed image can be distorted depending on the ratio (w/h)

  31. Matrix Stacks Pushing and Popping the Matrix Stack • A stack of matrices is useful for constructing hierarchical models, in which complicated objects are constructed from simpler ones. • glMatrixMode() • glLoadMatrix(), glMultMatrix() • glPushMatrix(), glPopMatrix() • glLoadIdentity() Modelview and Projection Matrix Stacks

  32. Matrix Stacks Example (0.0, 0.0, 0.0) glPushMatrix() (0.0, 0.0, 0.0) glTranslatef() CreateTriangle CreateCircle glLoadIdentity() (0.0, 0.0, -5.0) (0.0, 0.0, 0.0) CreateCircle CreateCircle

  33. How to program? • Need OpenGL Extensions • Win32 OS: WGL. Prefix starting with wgl. (brief explanation at MSDN) • X Windows: GLX • Apple Macintosh: AGL • OS/2: PGL • Each extensions supports making windows-based applications depending on operating systems. • But, it has restrictions of broadly using in other operating systems.

  34. What is GLUT? • OpenGL Utility Toolkit • A window system independent toolkit for writing OpenGL programs. • Works across all PC and workstation OS platforms • http://www.opengl.org/resources/libraries/glut.html • Better than AUX (Auxiliary) library • Need to locate the header and library files when using Windows Operating System (not obligation, but useful when making OpenGL applications) • (*.dll) C:\WINDOWS\system32 • Vs6 : • (*.h) C:\Program Files\Microsoft Visual Studio\VC98\Include\GL • (*.lib) C:\Program Files\Microsoft Visual Studio\VC98\Lib • .net • (*.h) C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\PlatformSDK\Include\gl • (*.lib) C:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\PlatformSDK\Lib

  35. How to use GLUT? • Initialization functions • void glutInit(int *argc, char **argv); • Initialize display mode • glutInitDisplayMode(unsigned int mode); • GLUT_RGB, GLUT_SINGLE, GLUT_DOUBLE • Set the initial size of the window • glutInitWindowSize(int width, int height); • The initial position of the window • glutInitWindowPosition(int x, int y); • Creates the window • int glutCreateWindow(char *name); • Specifying the function that needs to be called (callback function) • void glutDisplayFunc(void (*func)(void)); • Redraw the current window • void glutPostRedisplay(void); • A callback function called when window size is changed • void glutReshapeFunc(void (*func)(int width, int height)); • More info. at “An introduction to GLUT”, http://mindfuck.de-brauwer.be/articles/glut/

  36. #include<gl\glut.h> void DrawTriangle() { glBegin(GL_TRIANGLES); glColor3f(1.0f, 0.0f, 0.0f); // red glVertex2f(0.0f, 0.0f); glColor3f(0.0f, 1.0f, 0.0f); // green glVertex2f(1.0f, 0.0f); glColor3f(0.0f, 0.0f, 1.0f); // blue glVertex2f(0.0f, 1.0f); glEnd(); } void display() { glClearColor(0.0, 0.0, 0.0, 0.0); // black glClear(GL_COLOR_BUFFER_BIT); glPushMatrix(); // push modelview matrix glTranslatef(1.0f, 1.0f, 0.0f); glRotatef(45.0f, 0.5f, 1.0f, 0.5f); DrawTriangle(); glPopMatrix(); // pop modelview matrix glFlush(); } void reshape(int w, int h) { glViewport(0,0,w,h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-1.0, 1.0, -1.0, 1.0, 0.0, 100.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); gluLookAt(1.5f, 1.5f, 1.0f, 1.5f, 1.5f, -0.5f, 0.0f, 1.0f, 0.0f); } void init() { // Gouraud Shading glShadeModel(GL_SMOOTH); } void main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100,100); glutInitWindowSize(400,400); glutCreateWindow("OpenGL EXAMPLE"); init(); glutReshapeFunc(reshape); glutDisplayFunc(display); glutMainLoop(); } A simple example

  37. #include "glut.h" static int year = 0, day = 0; void display(void) { glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT); glColor3f (1.0, 1.0, 1.0); glPushMatrix(); glColor3f(1.0, 0.0, 0.0); glutSolidSphere(1.0, 10, 10);/* draw sun */ glRotatef((GLfloat) year, 0.0, 1.0, 0.0); glTranslatef (2.0, 0.0, 0.0); glRotatef((GLfloat) day, 0.0, 1.0, 0.0); glColor3f(0.0, 0.0, 1.0); glutSolidSphere(0.2, 10, 10);/* draw smaller planet */ glPopMatrix(); glFlush(); } void myinit(void) { glShadeModel(GL_SMOOTH); glEnable(GL_DEPTH_TEST); } void myReshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef (0.0, 0.0, -5.0); } void Key1(int key, int x, int y) { switch(key) { case GLUT_KEY_LEFT: year = (year - 5) % 360; break; case GLUT_KEY_RIGHT: year = (year + 5) % 360; break; case GLUT_KEY_UP: day = (day + 10) % 360; break; case GLUT_KEY_DOWN: day = (day - 10) % 360; break; } glutPostRedisplay(); } void main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100,100); glutInitWindowSize(400,400); glutCreateWindow("OpenGL EXAMPLE"); myinit(); glutReshapeFunc(myReshape); glutDisplayFunc(display); glutSpecialFunc(Key1); glutMainLoop(); } Transformation Example I

  38. OpenGL display lists are designed to optimize performance drawCircle() { GLint i; GLfloat cosine, sine; glBegin(GL_POLYGON); for(i=0;i<100;i++){ cosine=cos(i*2*PI/100.0); sine=sin(i*2*PI/100.0); glVertex2f(cosine,sine); } glEnd(); } buildCircle() { GLint i; GLfloat cosine, sine; glNewList(MY_CIRCLE_LIST, GL_COMPILE); glBegin(GL_POLYGON); for(i=0;i<100;i++){ cosine=cos(i*2*PI/100.0); sine=sin(i*2*PI/100.0); glVertex2f(cosine,sine); } glEnd(); glEndList(); } glCallList(MY_CIRCLE_LIST); Display List

  39. #include "glut.h" GLuint listName = 1; void display(void) { glClear(GL_COLOR_BUFFER_BIT); GLuint i; glColor3f(0.0, 1.0, 0.0); for (i = 0; i < 10; i++) glCallList (listName); glFlush (); } void myinit(void) { glShadeModel(GL_SMOOTH); glNewList (listName, GL_COMPILE); glColor3f(1.0, 0.0, 0.0); glBegin (GL_TRIANGLES); glVertex2f (0.0, 0.0); glVertex2f (1.0, 0.0); glVertex2f (0.0, 1.0); glEnd (); glTranslatef (1.2, 0.0, 0.0); glEndList (); } void myReshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); if (w <= h) gluOrtho2D (0.0, 2.0, -0.5 * (GLfloat) h/(GLfloat) w,1.5 * (GLfloat) h/(GLfloat) w); else gluOrtho2D (0.0, 2.0 * (GLfloat) w/(GLfloat) h, -0.5, 1.5); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } void main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100,100); glutInitWindowSize(400,400); glutCreateWindow("OpenGL EXAMPLE 2"); myinit(); glutReshapeFunc(myReshape); glutDisplayFunc(display); glutMainLoop(); } Transformation Example II

  40. Shading model • Flat shading • glShadeModel(GL_FLAT) • Smooth (Gouraud) shading • glShadeModel(GL_SMOOTH)

  41. Light source • Ambient (GL_AMBIENT) • The light from that source that's been scattered so much by the environment • Diffuse (GL_DIFFUSE) • Comes from one direction • Specular (GL_SPECULAR) • Comes from a particular direction GLfloat light_ambient[] = { 0.0, 0.0, 0.0, 1.0 }; GLfloat light_diffuse[] = { 1.0, 1.0, 1.0, 1.0 }; GLfloat light_specular[] = { 1.0, 1.0, 1.0, 1.0 }; GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 }; glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient); glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse); glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular); glLightfv(GL_LIGHT0, GL_POSITION, light_position);

  42. Material Properties • Define the material properties of the objects in the scene: • GL_AMBIENT, GL_DIFFUSE, GL_AMBIENT_AND_DIFFUSE, GL_SPECULAR, Etc. • GLfloat mat_amb_diff[] = { 0.1, 0.5, 0.8, 1.0 }; • glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE, mat_amb_diff);

  43. #include "glut.h" void display(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glutSolidSphere(1.0, 50, 50); glFlush(); } void myinit(void) { GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 }; GLfloat mat_shininess[] = { 50.0 }; GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 }; glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular); glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess); glLightfv(GL_LIGHT0, GL_POSITION, light_position); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glEnable(GL_DEPTH_TEST); } void myReshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); if (w <= h) glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w, 1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0); else glOrtho (-1.5*(GLfloat)w/(GLfloat)h,1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } void main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100,100); glutInitWindowSize(500,500); glutCreateWindow("OpenGL EXAMPLE 3"); myinit(); glutReshapeFunc(myReshape); glutDisplayFunc(display); glutMainLoop(); } Light Example I

  44. #include "glut.h" static int spin = 0; void display(void) { GLfloat position[] = { 0.0, 0.0, 1.5, 1.0 }; glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glPushMatrix (); glTranslatef (0.0, 0.0, -5.0); glPushMatrix (); glRotated ((GLdouble) spin, 1.0, 0.0, 0.0); glRotated (0.0, 1.0, 0.0, 0.0); glLightfv (GL_LIGHT0, GL_POSITION, position); glTranslated (0.0, 0.0, 1.5); glDisable (GL_LIGHTING); glColor3f (0.0, 1.0, 1.0); glutWireCube(0.1); glEnable (GL_LIGHTING); glPopMatrix (); glutSolidSphere(0.9, 50, 50); glPopMatrix (); glFlush (); } void myinit(void) { glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glEnable(GL_DEPTH_TEST); } void myReshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(40.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0); glMatrixMode(GL_MODELVIEW);} void Key1(int key, int x, int y) { switch(key) { case GLUT_KEY_LEFT: spin = (spin + 30) % 360; break; } glutPostRedisplay(); } void main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100,100); glutInitWindowSize(500,500); glutCreateWindow("OpenGL EXAMPLE 4"); myinit(); glutReshapeFunc(myReshape); glutDisplayFunc(display); glutSpecialFunc(Key1); glutMainLoop(); } Light Example II

  45. #include "glut.h" GLfloat diffuseMaterial[4] = { 0.5, 0.5, 0.5, 1.0 }; void display(void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glutSolidSphere(1.0, 50, 50); glFlush(); } void myinit(void) { GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 }; GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 }; glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial); glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular); glMaterialf(GL_FRONT, GL_SHININESS, 25.0); glLightfv(GL_LIGHT0, GL_POSITION, light_position); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glEnable(GL_DEPTH_TEST); glColorMaterial(GL_FRONT, GL_DIFFUSE); glEnable(GL_COLOR_MATERIAL); } void myReshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); if (w <= h) glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w,1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0); else glOrtho (-1.5*(GLfloat)w/(GLfloat)h,1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } void Mouse(int button, int state, int x, int y) { if (state == GLUT_DOWN) { switch (button) { case GLUT_LEFT_BUTTON : diffuseMaterial[0] += 0.1; if (diffuseMaterial[0] > 1.0) diffuseMaterial[0] = 0.0; glColor4fv(diffuseMaterial); break; case GLUT_RIGHT_BUTTON : diffuseMaterial[1] += 0.1; if (diffuseMaterial[1] > 1.0) diffuseMaterial[1] = 0.0; glColor4fv(diffuseMaterial); break; case GLUT_MIDDLE_BUTTON : diffuseMaterial[2] += 0.1; if (diffuseMaterial[2] > 1.0) diffuseMaterial[2] = 0.0; glColor4fv(diffuseMaterial); break; } } glutPostRedisplay(); } void main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100,100); glutInitWindowSize(500,500); glutCreateWindow("OpenGL EXAMPLE 5"); myinit(); glutReshapeFunc(myReshape); glutDisplayFunc(display); glutMouseFunc(Mouse); glutMainLoop(); } Light Example III

  46. Complicated Examples

  47. Complex Model I • Does it look complicated? • Only use simple shape models such as sphere, rectangle boxes, octagon, etc. • Configurations • Torso, Hip, Shoulder, RocketPod, UpperArm, ForeAm, UpperLeg, Foot, VulcanGun, Building models • Smooth animation • Only transformation functions

  48. Complex Model II • Environment • Loading the tunnel model • Add texture images • For navigation pre-calculated camera route used • Text • glfont library used Environmental map

  49. Complex Model III • Loading models • Use user-defined file format • Additional Features • Collision detection • Fog effects (OpenGL support)

  50. Complex Model IV • Loading models • Importing Wavefront OBJ file to display • *.obj file includes vertex, texture coordinate, and face numbers Rendered using 3DS MAX without texture Rendered using 3DS MAX with texture

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