CGLIB - Constraint-based Graphics Library

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CGLIB - Constraint-based Graphics Library

• Features
• Use constraints to specify the layouts of objects
• Use action rules to specify interactions
• Implementation
• Implemented in B-Prolog, Java, and C
• Applications
• Drawing editors, interactive user interfaces,
  document authoring, animation, information
  visualization, intelligent agents, and games.

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An Illustrative Example
go- cgButton(B), (1)
Btext Hello World!, (2) handleButtonClick(
B), (3) cgShow(B). (4)   handleButtonClick(B
), (5) actionPerformed(B) (6) gt
(7) halt. (8)
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Objects

• cgButton(X)
• Create a button X
• cgButton(X1,,Xn)
• Create a list of buttons

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Attributes of Objects
B is a button

• Base

• Derivative

y
Bwindow Bx By Bwidth Bheight Btext
Bcolor Bfont
BrightX BbottomY BcenterX BcenterY BleftTopPo
int BleftBottomPoint BrightTopPoint BrightBotto
mPoint Bcenter
x
height
width
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Constraints

• Arithmetic constraints
• O1x O1width//2 O2x
• O1centerX O2x
• Positioning constraints
• cgLeft(O1,O2)
• Same property constraints
• cgSame(O1,O2,size)
• cgSame(O1,O2,width,100)

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Constraints (Cont.)

• Grid constraints

cgGrid(_, S1,_, S2,S3,S4,
_,S5,_)
cgGrid(Bc,Bdiv,Bmul,Bsub, B7,B8, B9,
Badd, B4,B5, B6, Badd, B1,B2, B3,
Beq, B0,B0, Bdot,Beq,1,1),
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Constraints (Cont.)

• Table constraints

cgTable(Larc,Arc,Button,Lbutton,
Lcheckbox, Checkbox, Choice, Lchoice,
Lcircle,Circle,Image,Limage,
Llabel,Label,Line,Lline,
Llist,List,Oval,Loval,
Lrrectangle,Rrectangle,Rectangle,Lrectangle,
Lpolygon,Polygon,Square,Lsquare,
Lstar,Star,TextArea,Ltextarea,
Ltextfield,TextField,TextBox,Ltextbox,
Ltriangle,Triangle,_,_,20,20),
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Constraints (Cont.)

• Tree constraints

Tnode(C0,node(C1,node(C3,
node(C4,)), node(C2,node(C5,),
node(C6,))), cgTree(T,top_down,10,10,centered)
.
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Event Handling

• Action rule
• Examples

Agent ConditionSeq Event gt ActionSeq
handleButtonClick(B),actionPerformed(B) gt
handleMousePress(O),mousePressed(O,E)
gt Ex X, Ey Y, write(mouse_pressed
_at(X,Y)),nl. handleKeyType(O),keyTyped(O,E)
gt Echar Char, write(Char).
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Other Primitives in CGLIB

• Packing and showing objects
• cgPack(O) cgShow(O)
• Altering and moving objects
• Oattr Value
• cgScale(O,F) cgResize(O,W,H)
• cgMove(O,X,Y)
• Animation
• cgSleep(Time)
• Generating Java applets
• cgStartRecord(FileName) cgStopRecord

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Demo of CGLIB
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Related Work

• Postscript Latex
• Every detail must be specified
• Java Tcl/Tk
• Layout managers are helpful for certain layouts
• Functional programming
• New data types and functions for events, time,
  and behaviors
• Constraints Constraint programming
• Sketchpad, ThinkLab, Amulet, SubArctic

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Further Work

• Extension of the set of base objects
• Application-specific objects
• 3D objects
• Constructs for users to define their own objects
• Non-linear and soft constraints
• Improving the performance
• Constraint solving
• Graphics rendering

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Papers

1. N.F. Zhou CGLIB - A Constraint-based Graphics
   Library, Software - Practice and Experience, Vol.
   33, No.13, pp.1199-1216, 2003.
2. N.F. Zhou Authoring Graphics-rich and
   Interactive Documents in CGLIB - A
   Constraint-based Graphics Library, Proceedings of
   the ACM Symposium on Document Engineering,
   pp.28-38, November, 2001.