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# Practicing 2d drawing primitives

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### Practicing 2d drawing primitives

1. 1. MyTricksLab.com (Computer Science & Tech Tutorials) PRACTICING OPENGL- PRIMITIVES
2. 2. 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.
3. 3. 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();
4. 4. 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();
5. 5. OPENGL PRIMITIVES- LINESGL_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();
6. 6. OPENGL PRIMITIVES- LINESGL_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();
7. 7. OPENGL PRIMITIVES –GL_TRIANGESglColor3f(1.0,0.0,1.0);glLineWidth(4); -The default is GL_FILL for both front-and back-facing polygons.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 GL_POINT or or GL_FRONT_AND_BACK GL_FILL
8. 8. OPENGL PRIMITIVES –GL_TRIANGLE_STRIPglColor3f(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 triangleglEnd(); 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.
9. 9. OPENGL PRIMITIVES –GL_TRIANGLE_FANDraws 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();
10. 10. OPENGL PRIMITIVES –GL_QUADSNote: 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();
11. 11. 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();
12. 12. OPENGL PRIMITIVES –GL_POLYGONglBegin(GL_POLYGON); glVertex2f(2.0,1.0); glVertex2f(12.0,1.0); glVertex2f(14.0,3.0); glVertex2f(1.0,3.0);glEnd();
13. 13. CREATIVE DRAWING USING OPENGLPRIMITIVES
14. 14. LAB EXERCISE: TIME TO SHOW YOURCREATIVITY “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 Scene1. Use Open GL built in primitives to Implement your Designed virtual world (2D Scene). MyTricksLab.com (Computer Science & Tech Tutorials)