eMDL

1. eMDL Extended Motion Description Language

2. EMDL vs. MDL

3. MDL classic • Syntax: • line x1, y1, z1, x2, y2, z2 • Box x, y, z, dx, dy, dz • sphere x, y, z, r • move x, y, z [knob]

4. EMDL • Simple • Object Oriented • Robust • Supports Animation

5. # delcare filename filename sample_syntax; # fucntion definiitions function ears { sphere2=sphere1; sphere3=sphere1; sphere2.r=sphere1.r/2; sphere3.r=sphere1.r/2; save; } function moveout { move sphere3 <0,50,0>; sphere2.y=sphere2.y-50; save; } #more function definitions function moveback { sphere3.y=sphere3.y-50; sphere2.y=sphere2.y+50; save; } function movesideways { sphere3.x=sphere3.x-50; sphere2.x=sphere2.x+50; save; } function moveup { sphere3.y=sphere3.y-50; sphere2.y=sphere2.y-50; save; } Sample Syntax

6. # main body set sphere1 as sphere <150,150,150,50>; set sphere2 as sphere <100,100,100,100>; set sphere3 as sphere <100,100,100,100>; hide sphere2; hide sphere3; save; funct ears; repeat <2>{funct moveout;}; repeat <2>{funct moveback;}; repeat <2>{funct movesideways;}; repeat <2>{funct moveup;}; Sample Syntax (2)

7. Output

8. Output

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13. Output

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17. Structure of eMDL • Filename Specification • Function Declarations • Variable Declarations • Main Body

18. Filename Specification • Allows users to chose the filename for all MDL files that will be output • Must be the first line of the eMDL script • Optional : if not included, then the program will default to outputting tmp.mdl files.

19. Filename Specification (2) • Example : filename mdlTest; • Will result in all outputted MDL files named mdlTest<number>.mdl • <number> is enumerated based on how many times the save function was called in the code.

20. Function Declarations • If you want to create any functions, they must be declared and defined in the second section. • eMDL supports macro style functions with no parameters • Every function must have a unique identifier.

21. Function Declarations (2) • Function declarations consist of the keyword “function” followed by the identifying name • The function body is enclosed in curly braces and can contain of any combination of pre or user defined functions, assignments, or repeat clauses.

22. Function Declarations (3) • Example : function move50 { repeat <3> { move sphere1 <0, 50, 0>; move box2 <0, -50, 0>; save; } }

23. Variable Declarations • Must occur between the function declarations and the main body • All variables have a global scope. • Each variable must have its own unique identifier. • Five types of variables.

24. Variable Types • Integer set <name> as integer <value> • Box set <name> as box <x, y, z, dx, dy, dz> • Line set <name> as line <x, y, z, x2, y2, z2> • Sphere set <name> as sphere <x, y, z, r> • Torus set <name> as torus <x, y, z, r, R>

25. Main Body • This is where the actual graphic manipulations occur • Any variable declared previously can be changed and moved

26. Main Body (2) • Users may: • Utilize assignment statements • Call predefined functions • Call user defined functions • Create repeat blocks • Remove a variable • Save the current state to an MDL file

27. Details of our Compiler

28. Details of our Compiler • Lexer – splits code into tokens. • Parser – creates an AST. • TreeWalker – generates mdl Code • mdlParser – mdl Parser generates gif images. (compiled in C)

29. How We Implemented Our Compiler

30. emdlLexer • Lexer splits emdl code into tokens. • Some common tokens are: • INT • ID, which can be variable names and function names.

31. emdlParser • Parser makes an Abstract Syntax Tree out of the stream of tokens that the Lexer outputs. • Syntax is checked here. • The AST is designed and created here in the most efficient way for static semantic analysis to take place.

32. emdlTreeWalker • TreeWalker performs the static semantic analysis, as well as the code generation. • A linked list is created to hold all global variables. • The object in linked list knows what type of object the variable is, and all of its parameters.

33. emdlTreeWalker • A copy of the AST is made before we walk through the function declarations. • This is to facilitate function calls. • Each function call creates a copy of the this tree and call a treeWalker function on this tree. • Since our functions act like macros, the function body is just a sequential continuation of our code.

34. mdlParser • mdlParser is a binary executable that is compiled in C. • It asks the user for the names of an mdl file, and the name of the image file to be created. • It then outputs an image file for the given mdl file.

35. Comparison between emdl and mdl • One of the main reasons for the creation of this language was to extend mdl so that we could make the coding tighter and cleaner. • For the demo you had seen earlier, one emdl file created 9 separate mdl files, which created 9 separate image files.

36. Comparison between eMDL and mdl • Now if we had wanted to run the same animation, but with the two outside spheres being farther away from the interior sphere, I would only need to change on line in emdl. • But to do the same change in mdl would require us to modify all 9 of the mdl files that created this animation.

37. Testing • Tested during and after development.

38. During Development • Ran two test files when each new functionality was implemented. • One that ought to work • One that ought not and give errors • Didn’t always include all possible formations of newly implemented statements.

39. After Development • Created suite of test cases • Tested all legal formations of statements. • Tested for what we predicted to be common syntactic and semantic mistakes.

40. Lessons Learned • Compilers are harder to make than you might think. • Perpetual debugging and error-checking, since errors can and did crop up in the simplest functions.