Transcript Lecture 7. 2D Viewing • 2D viewing pipeline • Clipping window, • Normalization • viewport transformation • OpenGL 2D viewing functions • Setup clipping window, viewport •

Lecture 7. 2D Viewing
• 2D viewing pipeline
• Clipping window,
• Normalization
• viewport transformation
• OpenGL 2D viewing functions
• Setup clipping window, viewport
• Display window managing
• Clipping algorithms
– TWO-DIMENSIONAL POINT CLIPPING
– LINE CLIPPING
(1) Cohen-Sutherland Line Clipping
(2) Liang-Barsky Line Clipping
(3) Nicholl-Lee-Nicholl Line Cliping
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2D viewing pipeline
• Transformation vertices from MC to DC in five stages
MC
Construct WC
scene using MC
transformation
WC
Convert WC
to VC
VC
Transform VC
to NC
NC
DC
Map NC
to DC
• Clipping window (world window, or viewing window)
The section of 2D scene selected for display
• Display window
• Viewport
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2D viewing pipeline transformations
MC
Construct WC
scene using MC
transformation
MC M mc ,wc
WC
Convert WC
to VC
VC
Transform VC
to NC
NC
S2  T3
V1
DC
Map NC
to DC
V
R  T1
WC
MC
S1  T2
WC
M 'mc,wc
V  S2  T3  S1  T2  R  T1  M mc,wc V1  M V1
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OpenGL 2D viewing functions
• OpenGL has no specific functions for 2D viewing. 2D
viewing is a special case of 3D viewing
glMatrixMode(GL-PROJECTION)
• Designate the projection matrix as the current matrix.
Which is originally the identity matrix. Set the current
matrix as identity matrix
glLoadIdentity();
• GLU clipping window function
gluOrtho2D(xwmin, xwmax, ywmin, ywmax);
• OpenGL viewport function
glViewport(xvmin, yvmin, vpWidth, vpHeight);
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GLUT display window functions
•
Set Color mode, buffer mode
•
glutInitDispalyMode(GLUT_SINGLE | GLUT_RGB);
glClearColor(red, green, blue, alpha);
glClearIndex(index);
Display-window identifier
glutSetWindow(windowID);
•
currentWindowID = glutGetWindow();
Deleting a GLUT display window
•
glutDestroyWindow(windowID);
Relocate and resize
glutPositionWindow(x, y);
glutReshapeWindow(newWidth, newHeight);
•
Display window relocate, and resize
glutFullScreen();
glutReshapeFunc(winreshapFcn);
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Managing multiple GLUT display windows
glutIconifyWindow();
glutSetIconTitle(“Icon Name”);
glutSetWindowTitle(“New window name”);
glutPopWindow();
glutPushWindow();
glutHideWindow();
glutShowWindow();
glutCreateSubWindow(……)
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Clipping algorithms
• Clipping: Generally, any procedure that identifies those
portions of a picture that are either inside or outside of a
specified region of space is referred as a clipping
algorithm, or simply clipping.
• Types of Clipping:
–
–
–
–
–
Point clipping
Line Clipping (straight-lines Segments)
Area Clipping (Polygons, Curve-boundary Areas)
Curve Clipping
Text Clipping
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Point clipping
• Given a point P=(x, y), we display the point if the
following inequalities are satisfied:
xwmin <= x <= xwmax
ywmin <= y <= ywmax
where (xwmin, xwmax , ywmin , ywmax ) defines the
clipping window position in WC or SC.
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Line Clipping
•
Possible relationships between line positions and a clipping
rectangle:
1.
2.
3.
4.
Totally out
Totally in
in-and-out
out-in-out
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