PRACTICING OPENGL- PRIMITIVES

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OPENGL OUTPUT PRIMITIVES

Each geometric object is described by a set of vertices and the type of primitive to be drawn. Whether and how the vertices are connected is determined by the primitive type.

OPENGL PRIMITIVES- GL_POINTS

Lab Activity (1): Add the following code to display() method.

glPointSize(4.0); /* specify point to be 4 pixels thick */

glBegin(GL_POINTS);glVertex2f(0.0f, 2.0f); //note 2D form glVertex2f(1.0f, 2.0f);glVertex2f(0.0f, -2.0f);glVertex2f(-1.0f, 0.0f);

glEnd();

OPENGL PRIMITIVES- LINES Three different line primitives can be created:

GL_LINES: glColor3f(0.0,0.0,0.0);glLineWidth(5.0);

glBegin(GL_LINES);glVertex2f (-20.0, -20.0); glVertex2f (20.0, 20.0);

glColor3f(1.0,1.0,0.0);glVertex2f (10.0, -20.0);glVertex2f (10.0, 20.0);

glEnd();

OPENGL PRIMITIVES- LINES

GL_LINE_STRIP: Draws a connected set of line segments from the first vertex to the last.

glColor3f(0.5,0.6,0.0);glLineWidth(4);glBegin(GL_LINE_STRIP);

glVertex2f (5.0, 10.0);glVertex2f (10.0, 10.0);glVertex2f (10.0, 0.0);glVertex2f (5.0, 0.0);

glEnd();

OPENGL PRIMITIVES- LINES

GL_LINE_LOOP:glColor3f(0.9,0.8,0.0);glLineWidth(4);glBegin(GL_LINE_LOOP);

glVertex2f (-10.0, 9.0);glVertex2f (5.0, 9.0);glVertex2f (5.0, -1.0);glVertex2f (-10.0, -1.0);

glEnd();

OPENGL PRIMITIVES –GL_TRIANGES

glColor3f(1.0,0.0,1.0);

glLineWidth(4);

glBegin(GL_TRIANGLES);glVertex2f (-10.0, -10.0);glVertex2f (-5.0, -10.0);glVertex2f (-5.0, -5.0);

glEnd();

Insert this command before glLineWidth, and note the effect.

glPolygonMode(GL_FRONT, GL_LINE);

GL_BACK or GL_FRONT_AND_BACK

GL_POINT or GL_FILL

-The default is GL_FILL for both front-and back-facing polygons.

OPENGL PRIMITIVES –GL_TRIANGLE_STRIP

glColor3f(0.0,1.0,0.0);

glLineWidth(4);

glPolygonMode(GL_FRONT, GL_LINE);

glBegin(GL_TRIANGLE_STRIP);

glVertex2f (-10.0, -10.0);

glVertex2f (-19.0, -10.0);

glVertex2f (-10.0, -20.0);

glVertex2f (-18.0,-19.0); //create 2ndtriangle

glVertex2f (-5.0, -25.0); //create 3rd triangle

glVertex2f (-20.0, -29.0); //create 4th triangle

glEnd();

Note: • Order of points does matter!• If the vertices are defined clockwise, the front of the polygon will be shown. Otherwise, the back of the polygon will be shown.

OPENGL PRIMITIVES –GL_TRIANGLE_FAN

Draws a connected set of triangles. One triangle is defined for each vertex presented after the first two vertices.

Note: Order of points does matter!glColor3f(0.0,0.0,1.0);glLineWidth(4);

/* draw only the outline of polygon */glPolygonMode(GL_FRONT, GL_LINE);

glBegin( GL_TRIANGLE_FAN);glVertex2f (12.0, -30.0); glVertex2f(30.0, -30.0); glVertex2f (30.0, -20.0);glVertex2f (22.0, -15.0);glVertex2f (12.0, -12.0);

glEnd();

OPENGL PRIMITIVES –GL_QUADS

Note: Order of points does matter!

/* creating 2 quadrilaterals */ glColor3f(0.0,0.0,0.0);glPolygonMode(GL_FRONT, GL_LINE);glLineWidth(4);glBegin( GL_QUADS );

glVertex2f (-28.0, 25.0);glVertex2f (-28.0, 10.0);glVertex2f (-20.0, 10.0);glVertex2f (-20.0, 20.0);

glVertex2f (-15.0, 20.0);glVertex2f (-2.0, 20.0);glVertex2f (-2.0, 28.0);glVertex2f (-15.0, 28.0);

glEnd();

OPENGL PRIMITIVES –GL_QUAD_STRIP

/* creating 2 quadrilaterals using GL_QUAD_STRIP */

glColor3f(0.0,1.0,1.0);

glPolygonMode(GL_FRONT, GL_LINE);

glLineWidth(4);

glBegin( GL_QUAD_STRIP);glVertex2f (20.0, 10.0);

glVertex2f (29.0, 13.0);

glVertex2f (18.0, 20.0);

glVertex2f (26.0, 20.0);

glVertex2f (22.0, 25.0);

glVertex2f (30.0, 25.0);

glVertex2f (15.0, 30.0);

glVertex2f (35.0, 30.0);

glEnd();

OPENGL PRIMITIVES –GL_POLYGON

glBegin(GL_POLYGON);glVertex2f(2.0,1.0);glVertex2f(12.0,1.0);glVertex2f(14.0,3.0);glVertex2f(1.0,3.0);

glEnd();

CREATIVE DRAWING USING OPENGL PRIMITIVES

LAB EXERCISE: TIME TO SHOW YOUR CREATIVITY

“Sample 2D Scenary are given Lab folder”

1. Show your best to Design your virtual World (2D Scene) onto graph paper.

With Well defined coordinates Points of each object in Scene.

Also Define Color of each Object Of Your Scene

2. Use Open GL built in primitives to Implement your Designed virtual world (2D Scene).

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