1. Graphics Output Primitives
Sang Il Park
Sejong University

2. 2D Fill-Area Primitives

3. Irregular curved fill region
Fill-Area Primitives
Circular fill region
Irregular curved fill region
Polygonal fill
region
Tessellation

4. POLYGON
Polygon: a plane figure specified by a set of vertices connected with sequence of straight-line segments ex) triangles, rectangles, pentagons, octagons, ...
How to represent: a sequence of the vertices ( vertex list )

5. Polygon Representation
Using Tables:
1. Vertex table, edge table, surface table
2. Vertex table, surface table

6. OpenGL polygon fill-area functions
Rectangular fill area:
glRect* (x1,y1,x2,y2)
glRecti (50, 50, 200, 200)
int pt1 [] = {50, 50};
int pt2 [] = {200,200};
glRectiv (pt1, pt2);

7. OpenGL polygon fill-area functions
OpenGL에서의 그림 그리기는 다음과 같은 Begin-End 절로 표현 예)
glBegin (종류);
………
glEnd ( );
GL_POLYGON
GL_TRIANGLES
GL_TRIANGLE_STRIP
GL_TRIANGLE_FAN
GL_QUADS
GL_QUAD_STRIP
glBegin (GL_POLYGONS);
glVertex2iv (pt1);
glVertex2iv (pt2);
glVertex2iv (pt3);
glVertex2iv (pt4);
glVertex2iv (pt5);
glEnd ( );

8. OpenGL Vertex Arrays An efficient way to send the vertex data
glEnableClientState (GL_VERTEX_ARRAY);
glVertexPointer (2, GL_INT, 0, pt);
GLubyte vertIndex [] = {1, 2, 3, 4,
4, 3, 5, 6};
glDrawElements (GL_QUADS,8,
GL_UNSIGNED_BYTE, vertIndex);

9. OpenGL Display List An comvenient, efficient way to store an object
Execute a display list:
glNewList (listID, listMode );
// your drawing routine
glEndList();
listID: a unique name for the list (GLuint) Use glGenLists(1) to obtain a valid ID
listMode: GL_COMPILE / GL_COMPILE_AND_EXECUTE
glCallList(listID);

10. GLUT display reshape function
Reshape (or resize) callback: when changing the window size
Registration:
Implementation:
glutReshapeFunc ( MyReshape );
void MyReshape (int w, int h) {
// your reshaping code such as gluOrtho2D }

11. OpenGL Pixel-Array Primitives
Bitmap: using a bit for representing each pixel
Pixmap: using several bytes for each pixel

12. OpenGL Pixel-Array Primitives
glBitmap: draw a bitmap on the screen
Glubyte bitmap [20] = {
0x1c,0x00,0x1c,0x00,0x1c,0x00,0x1c,0x00,
0x1c,0x00,0xff,0x80,0x7f,0x00,0x3e,0x00,
0x1c,0x00,0x08,0x00};
glPixelStorei (GL_UNPACK_ALIGHMENT, 1);
glRasterPos2i(30,40);
glBitmap( 9, 10, 0.0, 0.0, 20.0, 15.0, bitmap);

13. OpenGL Pixel-Array Primitives
glDrawPixels: draw a pixmap on the screen
glDrawPixels ( width, height,
dataFormat, dataType, pixMap);

14. Text-Drawing Painting programs Drawing programs
bit-mapped representation
e.g., Adobe Photoshop, bit-map fonts
Drawing programs
object-based representation
e.g., Powerpoint, outline fonts

15. OpenGL Text Drawing Bitmap text: Ex) glutBitmapCharacter (font, char )
GLUT_BITMAP_8_BY_13
GLUT_BITMAP_9_BY_15
GLUT_BITMAP_TIMES_ROMAN_10 …
char a[]=“abced”;
glrasterPosition2i(100,100);
for(int i=0;i<5;i++)
glutBitmapCharacter (GLUT_BITMAP_8_BY_13, a[i]);

16. 연습 교재 page 181~189 까지 직접 입력해서 실행해 보고, 그 내용을 분석해 볼 것

17. Ch.4. Attributes of Graphics Primitives

18. OpenGL State variables:
Color
Point attributes
Line attributes
Fill-Area attributes

19. Color in OpenGL Color buffer Setting: Setting the color value: Ex)
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB)
GLUT_RGBA
GLUT_RGB
GLUT_INDEX
GLUT_SINGLE
GLUT_DOUBLE
glColor* (values);
glColor3f (0.0, 1.0, 0.5);
glColor3i ( 0, 255, 128);

20. Point Attributes in OpenGL
Size:
Color :
glPointSize ( size );
glColor* (values);

21. Line Attributes in OpenGL
Width:
Line-Style : ex)
Line-Style On/Off:
glLineWidth ( width );
glLineStipple (repeatFactor, pattern);
glLineStipple (1, 0x00FF);
glLineStipple (1, 0x0101);
glEnable (GL_LINE_STIPPLE);
glDisable (GL_LINE_STIPPLE);

22. Other Line Attributes Not in OpenGL
Line Caps:
Connecting:
Butt cap
Round cap
Projecting square cap
Miter join
Round join
Bevel join

23. Other Line Attributes Not in OpenGL
Pen and Brush Options:

24. Color in OpenGL Color buffer Setting: Setting the color value: Ex)
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB)
GLUT_RGBA
GLUT_RGB
GLUT_INDEX
GLUT_SINGLE
GLUT_DOUBLE
glColor* (values);
glColor3f (0.0, 1.0, 0.5);
glColor3i ( 0, 255, 128);

25. Area Filling
Scan line approach
Seed Fill Algorithm

26. Area Filling (Scan line Approach)
For each scan line
(1) Find intersections (the extrema of spans)
Use Bresenham's line-scan algorithm
(2) Sort intersections (increasing x order)
(3) Fill in between pair of intersections

27. Area Filling (Scan line Approach)
Take advantage of
Edge coherence: edges intersected by scan line i are also intersected by scan line i+1

28. Area Filling (Scan line method)

29. Area Filling (Seed Fill Algorithm)
basic idea
Start at a pixel interior to a polygon
Fill the others using connectivity
seed

30. Seed Fill Algorithm (Cont’)
4-connected
8-connected
Need a stack.
Why?

31. Seed Fill Algorithm (Cont’)
start position

32. Seed Fill Algorithm (Cont’)8 6 4 2 8 6 4 2
interior-defined
boundary-defined
flood fill algorithm
boundary fill algorithm

33. Seed Fill Algorithm (Cont’) 1 2 3 4 5 6 7 1 2 3 4 5 6 7
hole
boundary pixel
interior pixel
seed pixel
The stack may contain duplicated or unnecessary information !!!

34. Boundary Filling

35. Flood Filling
: Start a point inside the figure, replace a specified interior color only.

36. Scan Line Seed Fill scan line conversion seed filling +
Shani, U., “Filling Regions in Binary Raster Images:
A Graph-Theoretic Approach”, Computer Graphics,
14, (1981),

37. Boundary Filling Efficiency in space!
finish the scan line containing the starting position
process all lines below the start line
process all lines above the start line

38. Problems of Filling Algorithm
What happens if a vertex is shared by more than one polygon, e.g. three triangles?
What happens if the polygon intersects itself?
What happens for a “sliver”?
Solutions?
Redefine what it means to be inside of a triangle
Different routines for nasty little triangles

39. Aliasing in CG
Which is the better?