1 glBegin( ) Param eters glBegin( ) Param eters glBegin(GL_LI - - PDF document

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CS 4 7 3 1 Lecture 3 : I ntroduction to OpenGL and GLUT: Part I I Emmanuel Agu OpenGL Draw ing

• OpenGL drawing usually done in display function
• Display function is called once when program starts
• Recall that first, register callback in m ain( ) function

glutDisplayFunc( display );

• Then, im plem ent display function

void display( void ) { // put drawing stuff here ……. glBegin( GL_LINES ); glVertex3fv( v[0] ); glVertex3fv( v[1] ); …………… glEnd(); }

Basic Draw ing Prim itives

• Draw points, lines, polylines, polygons
• Prim itives are specified using form at:

glBegin(primType) // define your primitives here glEnd( )

• primType: GL_POINTS, GL_LINES, GL_POLYGON….

Basic Draw ing Prim itives: Exam ple

• Exam ple: to draw three dots:

glBegin(GL_POINTS) glVertex2i(100,50) glVertex2i(100,130) glVertex2i(150, 130) glEnd( )

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glBegin( ) Param eters

glBegin(GL_POI NTS)

– draws dots

glBegin(GL_LI NES)

– draws lines

glBegin( ) Param eters

glBegin(GL_LI NE_STRI P)

– polylines

glBegin( GL_POLYGON)

– convex filled polygon

glBegin( ) Param eters

• GL_POI NTS - dots
• GL_LI NES – lines, in pairs
• GL_LI NE_STRI P – polylines
• GL_LI NE_LOOP – closed loop
• GL_TRI ANGLES – triangles, three vertices
• GL_QUADS – quad, four vertices
• GL_POLYGON – convex filled polygon

OpenGL Com m and Form at glVertex2i(… )

basic command

Vertex Color Clear Flush

number of argum ents

2 – (x,y) 3 – ( x,y,z) 4 – (x,y,z,w) or (r,g,b,a)

type of argum ent

b – byte ub- unsigned byte s - short us – unsigned short i – int ui – unsigned int f – float d - double * - wildcard

library

gl glu glut

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Som e OpenGL Com m ands

• glVertex2i( ) – x,y vertex position
• glColor3f( ) – RGB color
• glRecti( ) – aligned rectangled
• glClearColor – clear color in RGB
• glClear( ) – clears screen
• glFlush( ) – forces im age drawing

OpenGL Data Types

GLuint Unsigned int GLushort Unsigned short GLubyte Unsigned char GLDouble Double GLFloat Float GLInt Int GLShort Short GLByte Signed char OpenGL C+ +

Mouse I nteraction

• Declare prototype
• myMouse(int button, int state, int x, int y)
• myMovedMouse
• Register callbacks:
• glutMouseFunc(myMouse): when mouse button pressed
• glutMotionFunc(myMovedMouse): when mouse moves
• Button returned values:
• GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON,

GLUT_RIGHT_BUTTON

• State returned values:
• GLUT_UP, GLUT_DOWN
• X,Y returned values:

Keyboard I nteraction

• Declare prototype
• myKeyboard(unsigned int key, int x, int y)
• Register callback:
• glutKeyboardFunc(myKeyboard): when keyboard is pressed
• Key values:
• ASCII value of key pressed
• X,Y values:
• Coordinates of mouse location
• Large switch statem ent to check which key

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Exam ple: Keyboard Callback

• How to use keyboard to control program ?
• 1. register callback in m ain( ) function

glutKeyboardFunc( myKeyboard );

• 2. im plem ent keyboard function

void myKeyboard(char key, int x, int y ) { // put keyboard stuff here ………. switch(key){ // check which key case ‘f’: // do stuff break; } …………… }

OpenGL State

• OpenGL tracks states
• Drawing color
• Point size
• Rendered objects appearance based on current state
• State variable rem ains active till changed

m iniGL: W h a t ?

• Object- oriented wrapper in C+ +
• Allows you choose to either:

• First few projects will use pure openGL option
• Later, you will learn the algorithm s and im plem ent som e

OpenGL calls

• Google note: there exists another m iniGL, OpenGL port to

PDAs

m iniGL: How ?

• Can run executables (gears, bounce, your code) using two
• ptions:
• ope n GL opt ion sim ply ca lls pur e Ope nGL ca ll
• cs4 7 3 1 GL opt ion ca lls y ou r code
• I n beginning, both options are set up to call pure OpenGL

call

• Later, you will replace some parts, which are called by –

cs4731GL option (* gulp!!* )

• Exam ple:

hom e_grown_glRotate

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m iniGL: How ?

• m iniGL advantage: debugging, can test sam e code using

both pure calls and your code

• How? When coding your functions, can always use –openGL
• ption to debug
• Design:

• Examples:

m iniGL: W ho?

• m iniGL written initially by Mark Stevens
• Stevens, previously CS professor, taught this class before
• m iniGL extended by Em m anuel Agu
• Som e students (Paul Tessier, Tony Andrade, etc) subm itted

bug fixes, corrections, etc

• miniGL m ostly stable, been used in this course 3 or 4

previous times

Hom ew ork 1

• On class website
• Goal: to get you going, work out platform issues!!
• Get OpenGL and GLUT
• Set up your program m ing environm ent
• Com pile m iniGL code
• Examples:
• Read sect ions of Hill book
• Convert exam ples t o m iniGL form at
• Derive new HW1 class ( from cs4731app class)
• Modify m iniGL draw funct ion
• Type in m issing funct ion( s)
• Com pile and run

Hom ew ork 1

• I f you called OpenGL calls directly, it would work
• Don’t make openGL calls directly
• Always m ake call to m iniGL
• For exam ple:

• miniGL calls either call openGL calls or cs4731app (your

hom e- grown functions).

• Due on Friday, Sept. 5, 2003

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References

• Hill, chapter 2