opengl basic functions

8/9/2019 OpenGL Basic Functions

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Simple OpenGLSimple OpenGL

FunctionsFunctions


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Outline

Todaydrawing lines, polygons, etc

setting colors,clearing the screen

Next Class

skeleton of an applicationcompiling OpenGL

simple movement


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OpenGL Libraries

gl - opengl

glut - windowing functions

glu - common objects and procedures

glux - interface to X for glut


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command format

glVertex3f (1.0, 0.25, 0.333);

gl library first letter of a function is always small

specify a point first letter of command is always capitalied

! parameters parameters types are floats

see parameter types on next page


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"arameter #ypes

b $-bit integer GLbyte

s %&-bit integer GLshort

i !'-bit integer GLintf !'-bit float GLfloat

d &(-bit float GLdouble

ub $-bit unsigned int GLubyte

us %&-bit unsigned int GLushort

ui!'-bit unsigned int GLuint


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example

#o set the drawing color to blue

glColor3f ( 0.0, 0.0, 1.0 );

or

GLfloat blue[] = {0.0, 0.0, 1.0};

glColor3fv (blue);


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)learing the *creen

glClearColor ( R, G, , ! )

glClear (GL"C#L#R"$%%&R"')

to clear to black, use RGBA values of 0.0

later in the semester, you will also need to clear the Depth

Buffer along with the olor Buffer


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+rawing *tuff

gleg* ( drawing mode );

glVertex...

glVertex...

...gl&*+();

odesGL"#'-

GL"#L/G#-GL"L'-& GL"L'-&"R' GL"L'-&"L##

GL"R'!-GL& GL"R'!-GL&"R' "%!-

GL"$! GL"G$!"R'


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example - drawing lines

Given four points "., "%, "', and "!

GL/L012* GL/L012/*#30" GL/L012/LOO"

". "%

"! "'


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example - #riangles

%

.

'

!

(

4


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example - #riangle *trip

.

!

4

(

% '


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example - #riangle 5ans

%

.

'

!

(

4


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6now your Limitations

Don't try to draw this star as a single polygon is "! inside the star or outside7

is "., "%, "' going clockwise or counterclockwise7

".

"%

"'

"!


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)olor 0nterpolation

gleg* (GL"L'-&)

glColor3f (1.0,0.0,0.0); re+

gl4erte2f(1.0,0.0);

glColor3f (1.0,1.0,0.0); 6ello7 gl4erte2f(0.0,1.0);

gl&*+();

8e get a line that starts out red and turns yellowassuming we left the default as gl8a+e9o+el (GL"9##:) instead of GL"%L!


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Line "roperties

Changing the width glL*e+t8 (float)

default is %9. Creating dashed and dotted lines gl&*able (GL"L'-&"'L&)

gltor,


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"olygon "roperties

Fill Pattern gl&*able (GL"#L/G#-"'L&)

glol6go*tle ( ?a


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5lushing

8hen you are done, don>t forget to flush

gl%lu


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bigger example

creating a cone ?ow can 0 create a @smooth@ cone7

use a triangle fan with lots of triangles


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!" !" !#

!" !" $%!#

x" y" $%!#x" y" $%!#

So" how do we compute a &unch o (alues or x and y)


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*

+Given that2 B 62 = r2

then

62 = r2 2

y = sqrt (r2 - x2)

*o, we run a loop where x changes, and compute the y valueA 5or example, with r B '., and x B %., then y B %C

6 =


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gleg* (GL"R'!-GL&"%!-);

glColor3f (1.0, 0.0, 0.0);

gl4erte3f (0.0,0.0,0.0); glColor3f (0.0, 1.0, 1.0);

ra+u< = 20

for (=20; =20; =5)

{

6 =

opengl basic functions

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