1. CSC 307 1.0 Graphics Programming
Budditha Hettige
Department of Statistics and Computer Science

2. Graphics Programming 2D Drawing03
Graphics Programming 2D Drawing

3. Primitive Types GL_POINTS GL_LINES GL_TRIANGLES GL_TRIANGLE_STRIP
GL_QUAD_STRIP
GL_LINE_STRIP
GL_LINE_LOOP
GL_QUADS
GL_POLYGON
GL_TRIANGLE_FAN

4. Points
point is represented by a set of floating-point numbers called a vertex
glBegin(GL_POINTS);
glVertex2f(0.0, 0.0);
glVertex2f(0.0, 3.0);
glVertex2f(4.0, 3.0);
glVertex2f(6.0, 1.5);
glVertex2f(4.0, 0.0);
glEnd();

5. Lines (GL_LINES)
Pairs of vertices interpreted as individual line segments

6. Lines (GL_LINE_STRIP)
Series of connected line segments

7. Lines (GL_LINE_LOOP)
Same as GL_LINE_STRIP, with a segment added between last and first vertices

8. Line Details Specify lines with different widths and lines
void glLineWidth(GLfloat width);
Stippled Lines
void glLineStipple(GLint factor, GLushort pattern);
glEnable(GL_LINE_STIPPLE);

9. Example
glEnable(GL_LINE_STIPPLE); glLineStipple(1, 0x0101); /* dotted */ glLineStipple(1, 0x00FF); /* dashed */ glLineStipple(1, 0x1C47); /* dash/dot/dash */ glLineStipple(1, 0x0101); glBegin(GL_LINE_LOOP); glVertex2f(-0.5, -0.5); glVertex2f(-0.5, 0.5); glVertex2f(0.5, 0.5); glVertex2f(0.5, -0.5); glEnd();

10. Triangles (GL_TRIANGLES)
Triples of vertices interpreted as triangles

11. OpenGL 2D-Drawing glBegin(GL_TRIANGLES); glEnd();
glVertex2f(-0.20f, 0.0f);
glVertex2f(0.20f, 0.0f);
glVertex2f(0.0f, 0.40f);
glVertex2f(-0.60f,-0.20f);
glVertex2f(-0.20f,-0.40f);
glVertex2f(0.0f, -0.80f);
glVertex2f(0.20f, -0.40f);
glVertex2f(0.60f, -0.20f);
glEnd();

12. Triangles (GL_TRIANGLE_STRIP)
Linked strip of triangles

13. Triangles (GL_TRIANGLE_FAN)
Linked fan of triangles

14. Quad-(GL_QUADS)
Quadruples of vertices interpreted as four-sided polygons

15. Quads (GL_QUAD_STRIP)
Linked strip of quadrilaterals

16. Polygon (GL_POLYGON)
Boundary of a simple, convex polygon

17. Polygon Details Points, Outlines, or Solids
void glPolygonMode(GLenum face, GLenum mode);
Face
GL_FRONT_AND_BACK, GL_FRONT, or GL_BACK
Mode
GL_POINT, GL_LINE, or GL_FILL

18. Stippling Polygons Example
filled polygons are drawn with a solid pattern
void glPolygonStipple(const GLubyte *mask);
Example
Polygons.cpp
glEnable(GL_POLYGON_STIPPLE);
glPolygonStipple(fly);
glRectf(125.0, 25.0, 225.0, 125.0);
GLubyte fly[] = {
0x00, 0x00, 0x00, 0x00, 0x00,... };

19. OpenGL 2D-Drawing void display(void) { glClear (GL_COLOR_BUFFER_BIT);
glColor3f (1.0, 0.0, 0.0); // red
glBegin(GL_POLYGON);
glVertex2f(-0.20f, 0.50f);
glVertex2f(0.20f, 0.50f);
glVertex2f(0.50f, 0.20f);
glVertex2f(0.50f, -0.20f);
glColor3f (0.0, 0.0, 1.0); // blue
glVertex2f(0.20f, -0.50f);
glVertex2f(-0.20f, -0.50f);
glVertex2f(-0.50f, -0.20f);
glVertex2f(-0.50f, 0.20f);
glEnd();
glFlush (); }

20. RGB Color Space G R B Green (1,0,0) Yellow (1,1,0) White (1,1,1) Cyan
Image: Pixel maps to color
Green
(1,0,0)
Yellow
(1,1,0)
White
(1,1,1)
Cyan
(0,1,1)
Red
(1,0,0) R
Blk
Blue
(0,0,1)
Magenta
(1,0,1) B

21. Common Composite Colors

22. Colors
glColor3f(1.0, 0.0, 0.0);
The current RGB color is red: full red, no green, no blue.
RGB Display Modes

23. Specifying a Color and a Shading Model
RGBA mode, use the glColor*() command to select a current color.
void glColor3{b s i f d ub us ui}(TYPE r, TYPE g, TYPE b);
void glColor4{b s i f d ub us ui}(TYPE r, TYPE g, TYPE b, TYPE a);
void glColor3{b s i f d ub us ui}v(const TYPE *v);
void glColor4{b s i f d ub us ui}v(const TYPE *v);

24. Specifying a Shading Model
single color (flat shading)
many different colors (smooth shading, also called Gouraud shading)
void glShadeModel(GLenum mode);
GL_SMOOTH (the default) or GL_FLAT.
glShadeModel(GL_SMOOTH);
Example:
Shading.cpp