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OpenGL Primitives

Instructor: Marryam Murtaza

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The ten glBegin-style OpenGL Primitives

Points (1 primitive) GL_POINTS

Polylines (3 primitives) GL_LINES GL_LINE_STRIP

GL_LINE_LOOP

OpenGL Primitives

Filled Polygons (6primitives) Triangles

GL_TRIANGLES GL_TRIANGLE_STRIP

GL_TRIANGLE_FAN

Quadrilaterals

GL_QUADS GL_QUAD_STRIP

General Polygons GL_POLYGON

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A primitive is given a number of vertices speci!e" #ithglVertex$% &o# #e loo' at #hat the primitives "o #ith thevertices they are given%

&umbers in"icate verte( or"ering%

)lueob*ects mar' #hat is actually ren"ere"%

Points GL_POINTS

Attribtes

glPoint+ize,%$.

OpenGL Primitives: Points

/

0,1

23

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Polylines GL_LINES

GL_LINE_STRIP

GL_LINE_LOOP

OpenGL Primitives: Polylines

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0,1

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3

3

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2

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2

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4olor5 thic'ness5 stippling%

/% gl4olor2f$ sets color%

,% glLine6i"th1%$ sets thic'ness% The "efault thic'ness is/%%

2%

glLine+tipple15 7289$.1% glnableGL;LI&;+TIPPL$.

Line Attributes

a$% thin lines b$% thic' lines c$%stipple" lines

it is disabled by passing the same argumentto glDisable()

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Polygons: Triangles GL_TRIANGLES

4loc'#ise orcountercloc'#ise

"oes not matter yet$%

GL_TRIANGLE_STRIP

GL_TRIANGLE_FAN

OpenGL Primitives:Polygons !riangles

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, 1

2

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3

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,

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, 1

2

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Polygons in OpenGL

Triangles

glBegin(GL_TRIANGLES);

glVertex2fv(p0);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p4);

glVertex2fv(p5);

glVertex2fv(p6);

glVertex2fv(p7);

glEnd();

glBegin(GL_TRIANGLES);

glVertex2fv(p0);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p4);

glVertex2fv(p5);

glVertex2fv(p6);

glVertex2fv(p7);

glEnd();

p0p1

p2

p3

p4

p5

p6

p7

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OpenGL: !riangle "trips

An OpenGL triangle stripprimitive re"ucesthis re"un"ancy by sharing vertices:glBegin!GL_TRIANGLE_STRIP"#

glVertex$%&!&'"#

glVertex$%&!&("#glVertex$%&!&)"#

glVertex$%&!&$"#

glVertex$%&!&*"#

glVertex$%&!&+"#

glEn,!"#

v0

v2

v1

v3

v4

v5

triangle is v5 v/5 v,triangle / is v,5 v/5 v2 why not v1, v2, v3?$triangle , is v,5 v25 v1triangle 2 is v15 v25 v0 again5 notv25 v15 v0$

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OpenGL: !riangle Fan

The GL_TRIANGLE_FANprimitive is another #ay tore"uce verte( re"un"ancy:

v0

v1

v2

v3

v4

v5

v6

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gl)egin GL;T

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Polygons

>e!nition Ob*ect that is close" as in a line loop5 but that

has an interior

+imple Polygon &o pair of e"ges of a polygon cross each other

+imple &onsimple

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Polygons: ?ua"rilaterals

GL_QUADS

4loc'#ise orcountercloc'#ise"oes not matter yet$%

GL_QUAD_STRIP

&ote "i@erences inverte( or"ering

Polygons: General

GL_POLYGON

OpenGL Primitives:Polygons Quad#s$ General

/

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, 2

1

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3

/

0

,

1

2

,

B

3

/

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2

B

9

3

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Polygons in OpenGL

?ua"rilaterals

glBegin(GL_QUADS);

glVertex2fv(p0);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p4);

glVertex2fv(p5);

glVertex2fv(p6);

glVertex2fv(p7);

glEnd();

glBegin(GL_QUADS);

glVertex2fv(p0);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p4);

glVertex2fv(p5);

glVertex2fv(p6);

glVertex2fv(p7);glEnd();

p0p1

p2

p3

p4

p5

p6

p7

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Polygons in OpenGL

?ua"strip

glBegin(GL_QUAD_STRIP);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p0);

glVertex2fv(p4);

glVertex2fv(p7);

glVertex2fv(p5);

glVertex2fv(p6);

glEnd();

glBegin(GL_QUAD_STRIP);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p0);

glVertex2fv(p4);

glVertex2fv(p7);

glVertex2fv(p5);

glVertex2fv(p6);glEnd();

p0p1

p2

p3

p4

p5

p6

p7

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Polygons in OpenGL

Polygon

glBegin(GL_POLYGON);

glVertex2fv(p0);

glVertex2fv(p1);

glVertex2fv(p2);

glVertex2fv(p3);

glVertex2fv(p4);

glVertex2fv(p5);

glVertex2fv(p6);

glVertex2fv(p7);

glEnd();

glBegin(GL_POLYGON);

glVertex2fv(p0);

glVertex2fv(p1);

glVertex2fv(p2);glVertex2fv(p3);

glVertex2fv(p4);

glVertex2fv(p5);

glVertex2fv(p6);

glVertex2fv(p7);glEnd();

p0p1

p2

p3

p4

p5

p6

p7

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/% 6hat is the "i@erence bet#een

i% Cua"5

ii% Cua"strip an"

iii% polygons% Implement these using openGL

,% >ra# 1 rectangles using for loop%

Assignment