Introduction to OpenGL & HW1 Announcement 劉軒銘, 網媒所 碩二 ICG 2012 Fall

Introduction to OpenGL & HW1 Announcement 劉軒銘, 網媒所 碩二 ICG 2012 Fall Introduction to openGL Coordinate system and transformations in openGL A simple sample Requirements of HW1 Others

Introduction to openGL A Graphics rendering API introduced in 1992 by Silicon Graphics Inc Now managed by Khronos Group Provide the API functions to access graphics hardware directly Cross-platform

Introduction to openGL GLU (OpenGL Utility Library) ◦ Part of OpenGL ◦ Use the prefix of glu (ex: gluLookAt()) GLUT (OpenGL Utility Toolkit) ◦ Not officially part of OpenGL ◦ hide the complexities of differing window system APIs. ◦ Use the prefix of glut (ex:glutDisplayFunc())

World coordinates object coordinates Coordinate system

World coordinates Camera coordinates Coordinate system

World coordinates Camera coordinates Clip coordinates Coordinate system

Model-view transformati on Projection transformatio n Vertices World coordinates Camera coordinates Clip coordinates Vertices There are two matrix stacks. ◦ ModelView matrix (GL_MODELVIEW) ◦ Projection matrix (GL_PROJECTION) CTM

Coordinate system Model-view transformati on Projection transformatio n Vertices World coordinates Camera coordinates Clip coordinates Vertices glMatrixMode(GL_MODELVIEW); //now we are in modelview matrix stack! //do modelview transformation here….. glMatrixMode(GL_PROJECTION); //now we are in projection matrix stack! //do projection transformation here…. When we call functions of transformation, we should change to the appropriate matrix stack first.

openGL as state machine Put a value into various states, then it will remain in effect until being changed. ◦ e.g. glColor*() Many state variables are enabled or disabled with glEnable(), glDisable() ◦ e.g. glEnable(GL_LIGHT0)

openGL as state machine glBegin(GL_LINES); R G B glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); (1,1,0) (-1,-1,0) (-1,1,0) (1,-1,0)

openGL as state machine glLoadIdentity(); glTranslatef( distance,0, 0); glRotatef(angleX, 1.0, 0.0, 0.0); glRotatef(angleY, 0.0, 1.0, 0.0); glBegin(GL_QUADS); glVertex3f(-7, 7, 7); … glEnd(); (1,1,0) (-1,-1,0) (-1,1,0) (1,-1,0) Current Transformation matrix (CTM)

Matrix in OpenGL Mantain matrix stack ◦ glPushMatrix() : used to save current stack ◦ glPopMatrix() : used to restore previous stack glPushMatirx() x glRotatef glPopMatrix() 13

World coordinates glBegin(TYPE) glVertex3f(x,y,z) ……. glEnd() Coordinate system

Primitives

Transformations : Model-View glMatrixMode(GL_MODELVIEW) //Affine Transformation glRotatef(angle,direction) glTranslatef(displacement) glScalef(scale coefficients) glBegin(TYPE) glVertex3f(x,y,z) …………………. glEnd() World coordinates Camera coordinates V ’ <- [R][T][S] V

glMatrixMode(GL_MODELVIEW) gluLookAt({eye},{look at},{{up}) //Affine Transformation glBegin(TYPE) glVertex3f(v0) glEnd() World coordinates Camera coordinates Transformations : Model-View

glMatrixMode(GL_PROJECTION) //projection Transformation glOrtho(clipping volume) gluPerspective(fov,ciipping Volume) glFrustrum(clipping volume) glMatrixMode(GL_MODELVIEW) gluLookAt //Affine Transformation glBegin(TYPE) glVertex3f(v0) ……….. glEnd() World coordinates Camera coordinates Image coordinates Transformations : Projection

Notice!! Each affine and projective transformation is implemented as a matrix, the order of function calls plays an important role. glRotatef glTranslatef glScalef Code: glBegin glVertex3f …… glEnd Matrix multiplication gluLookAt glMatrixMode(GL_MODELVIEW) glMatrixMode(GL_PROJECTION) gluperspective = V gluLookAt glRotatef glTranslatef glScalef glVertex3f gluperspective

A Simple Example

#include int main(int argc, char** argv) { glutInit(&argc, argv); glutInitWindowSize(600, 800); glutInitWindowPosition(500, 500); glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE); glutCreateWindow("ICG simple"); glutReshapeFunc(GL_reshape); glutDisplayFunc(GL_display); glutMainLoop(); return 0; }

A Simple Example void GL_display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin( GL_LINES ); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); glutSwapBuffers(); }

A Simple Example void GL_display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin( GL_LINES ); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); glutSwapBuffers(); }

A Simple Example void GL_display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin( GL_LINES ); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); glutSwapBuffers(); }

A Simple Example void GL_display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin( GL_LINES ); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); glutSwapBuffers(); }

A Simple Example void GL_display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin( GL_LINES ); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); glutSwapBuffers(); }

A Simple Example void GL_reshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f); }

A Simple Example void GL_reshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f); }

A Simple Example void GL_reshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f); }

A Simple Example #include void GL_reshape(GLsizei w, GLsizei h); void GL_display(); int main(int argc, char** argv) { glutInit(&argc, argv); glutInitWindowSize(600, 800); glutInitWindowPosition(500, 500); glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE); glutCreateWindow("ICG simple"); glutReshapeFunc(GL_reshape); glutDisplayFunc(GL_display); glutMainLoop(); return 0; } void GL_reshape(GLsizei w, GLsizei h) { glViewport(0, 0, w, h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f); } void GL_display() { glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin( GL_LINES ); glColor3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0, 1.0, 0.0); glVertex3f(-1.0, -1.0, 0.0); glColor3f(1.0f, 0.0f, 0.0f); glVertex3f(-1.0, 1.0, 0.0); glVertex3f(1.0, -1.0, 0.0); glEnd(); glutSwapBuffers(); }

Requirements of HW1 Due : 10/24 You are required to do the following in homework #1: (6 points ) 1. Load a 3D model file of TRI format. Draw it in wireframe mode and view it in perspective view.(2 pts) 2. Implement basic transformations such as rotation, translation, scaling and shearing.(3 pts) 3. Object rotation around x, y and z-axis.(4 pts) ** You have to make these transformation matrix by yourself in problem 2 and 3 ** glTranslate, glRotate, glScale are not allowed 4. Clipping implementation. Try to show the difference between clipping and non- clipping. (5 pts) ** glOrtho, gluPerspective and glFrustum are not allowed in problem 4 5. Bonus. Any kind of effort you made more than requirements above.(6 pts)

z x y screen at z = 0 clipping box is enclosed by: x = 1,x=-1,y=1,y=-1,z=1,z=-1 Notice!! How does openGL set its clipping volume for window?? Using homogeneous coordinates clipping box nonhomogeneous coordinate: x y z w, w =/= 1

z x y screen at z = 0 clipping box is enclosed by: x = 1,x=-1,y=1,y=-1,z=1,z=-1 Notice!! How does openGL set its clipping volume for window?? Using homogeneous coordinates clipping box homogeneous coordinate: x/w y/w z/w 1

Notice!! How does openGL set its clipping volume for window?? Using homogeneous image coordinates clipping box You’d better set your own homogeneous image coordinates clipping box different from openGL’s. ※ Here the homogeneous image coordinates clipping volume is different from the One described in textbook, which is refer to camera coordinates clipping volume.

Others Glut window functions: glutInit(&argc, argv); glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutInitWindowSize(800, 600); glutInitWindowPosition(100, 100); glutCreateWindow(“Name"); glutDisplayFunc(display); glutReshapeFunc(reshape); glutKeyboardFunc(keyboard); glutMouseFunc(mouse); glutMainLoop();

Others Interactive setting: void keyboard(unsigned char key, int x, int y){ switch(key){ ……… case 'a': glClearColor(1., 1., 1., 1.); startPosX -= 10; glutPostRedisplay(); break; }

Others Interactive setting: void mouse(int button, int state, int x, int y){ static float preX, preY; switch(state){ case GLUT_DOWN: preX = x; preY = y; glutPostRedisplay(); break; ………………. }

Others Setting up openGL(visual C++): 1.download glut bin.zip or similar - GLUT for Win32 dll, lib and header file - there. 2.Make a directory called "GL" under C:\Program Files\Microsoft Visual Studio 9.0\VC\include or similar 3.Copy the header files into C:\programme\microsoft visual studio\vc98\include\GL 4.Copy all *.lib files into C:\programme\microsoft visual studio\vc98\Lib 5.Copy all.dll files into C:\Windows\System32 6.In the Menu of VC++ go through to -> project -> settings -> Link and add (do not remove the others!) the following libraries to the Object/libary modules line: glut32.lib glu32.lib opengl32.lib glaux.lib

Reference 1.Introduction to OpenGL PPT, Presented by Chung-Lin Wen ICG 2006 Fall 2.Interactive Computer Graphics – A Top-Down Approach Using openGL