This document discusses 2D graphics programming in OpenGL. It covers primitive types like points, lines, triangles, and polygons. It describes how to specify vertices to draw these primitive types and how to set properties like color, line width, and stippling. The RGB color space and methods for specifying color and shading models are also summarized.

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

2. Graphics Programming
2D Drawing
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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
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4. Points
• point is represented by a set of floating-
point numbers called a vertex
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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();
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5. Lines (GL_LINES)
• Pairs of vertices interpreted as individual
line segments
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6. Lines (GL_LINE_STRIP)
• Series of connected line segments
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7. Lines (GL_LINE_LOOP)
• Same as GL_LINE_STRIP, with a
segment added between last and first
vertices
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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);
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9. Example
glEnable(GL_LINE_STIPPLE);
glLineStipple(1, 0x0101); /* dotted */
glLineStipple(1, 0x00FF); /* dashed */
glLineStipple(1, 0x1C47); /* dash/dot/dash */
glEnable(GL_LINE_STIPPLE);
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();
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10. Triangles (GL_TRIANGLES)
• Triples of vertices interpreted as triangles
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11. OpenGL 2D-Drawing
glBegin(GL_TRIANGLES);
glVertex2f(-0.20f, 0.0f);
glVertex2f(0.20f, 0.0f);
glVertex2f(0.0f, 0.40f);
glVertex2f(-0.20f, 0.0f);
glVertex2f(-0.60f,-0.20f);
glVertex2f(-0.20f,-0.40f);
glVertex2f(-0.20f,-0.40f);
glVertex2f(0.0f, -0.80f);
glVertex2f(0.20f, -0.40f);
glVertex2f(0.20f, -0.40f);
glVertex2f(0.60f, -0.20f);
glVertex2f(0.20f, 0.0f);
glVertex2f(-0.20f, 0.0f);
glVertex2f(-0.20f,-0.40f);
glVertex2f(0.20f, 0.0f);
glVertex2f(-0.20f,-0.40f);
glVertex2f(0.20f, -0.40f);
glVertex2f(0.20f, 0.0f);
glEnd();
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12. Triangles (GL_TRIANGLE_STRIP)
• Linked strip of triangles
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13. Triangles (GL_TRIANGLE_FAN)
• Linked fan of triangles
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14. Quad-(GL_QUADS)
• Quadruples of vertices interpreted as four-
sided polygons
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15. Quads (GL_QUAD_STRIP)
• Linked strip of quadrilaterals
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16. Polygon (GL_POLYGON)
• Boundary of a simple, convex polygon
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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
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18. Stippling Polygons
• 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,... };
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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 ();
}
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20. RGB Color Space
Green
(1,0,0)
Blue
(0,0,1)
Red
(1,0,0)
Yellow
(1,1,0)
Magenta
(1,0,1)
Blk
Cyan
(0,1,1)
White
(1,1,1)
G
B
R
Image: Pixel maps to color
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21. Common Composite Colors
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22. Colors
• glColor3f(1.0, 0.0, 0.0);
– The current RGB color is red: full red, no green, no
blue.
– RGB Display Modes
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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);
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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
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