Slideshow: Functional Presentations
Contents
1. Nane Sgt Colon Home Ankh Morpork Name Detritus Home berwald We choose imperative registration through slide because a slide presentation is most easily written as a sequence of interleaved def initions and expressions much like the examples in Section 2 A programmer could thread a list through the sequence but such a threading is awkward to read and maintain The picts that are reg We illustrate the effect of slide by showing a framed scaled version of the resulting slide s pict istered for slides remain purely functional i e they cannot be mu tated so a small amount of imperative programming causes little problem in practice Furthermore we usually write slide at the top level interspersed with definitions so each use of slide feels more declarative than imperative The slide title function is similar to slide except that it takes an extra string argument The string is used as the slide s name and it is also used to generate a title pict that is placed above the supplied content picts The title pict uses a standard configurable font and is separated from the slide content by a standard amount slide title Depth First Search scale graph 3 Depth First Search ane Angua Name Sgt Colon Home Uberwald Home Ankh Morpork Name Brutha Home Omnia Name Detritus Home berwald In principle the slide2. ee Angus ce Set Colon see Ang see Set Colon oe berwald Ankh Morpork oe Uerwald xc Ankh Morpork mum mum ou s en Deis ou s er Desine From Brutha From Brutha Try Dotrius Try Detritus No Breadth First Search Breadth First Search soe Angus ee Set Colon so Angus ee Set Colon toe Uberwald toe Ank Morpok am Uerwal oe Ankh Morpork mem mem Mena p rem eis Moe fae Deis From Brutha From Brutha Try Sgt Colon Try Sat Colon Yes Breadth First Search From Brutha Tey Sat Colon Yos So we find Sgt Colon in Ankh Morpork 3 4 Adjusting Slide Defaults As we noted in Section 2 7 the font used by a pict cannot be changed after the pict is created because the pict s size depends on its font At first glance this constraint might limit the use func tions like para which do not accept a font specification and implic itly use t Slideshow makes para and other functions more useful through implicit parameters for t In particular the font used by t and bt and it is determined by the current main font pa rameter and the size is determined by the current font size parameter A parameter s value can be set during pict creation us ing the parameterize form For example if we wan
3. list make edge a find cb b find ct b make node brutha list make edge b find rt c find 1b make edge b find rc d find 1c c make node colon list make edge c find rc o find 1c d make node detritus list make edge d find ct c find cb o make node others list i The following search function takes the current stack of edges a list of previously visited edges to avoid cycles a target person to find an initial value for the search s result and a old like proce dure for accumulating the result with each traversal of an edge define search edges seen target v traverse if null edges v let e car edges next v traverse e v new remove append seen edges node edges edge to e if eq target node p edge to e next v search append new cdr edges cons e seen target next v traverse Using search we can now define graph by adding a gray connec tion to people each time that we traverse an edge while exploring the entire graph define line adder h lambda e p hconn p node p edge from e edge find from e node p edge to e edge find to e h define graph search node edges nodes list f people line adder dim Name Angua Name Sgt Colon Home Uberwald Home Ankh Morpork Name Brutha Home Omnia We can then create graph3 by searching for colon re adding con nections along the way in highlight
4. a pict As noted in Section 2 7 a pict s font cannot be changed ex ternally because changing the font would invalidate computations based on the pict s bounding box In a constraint based system or where all primitive pict combination operations are encapsulated in operations like vc append then invalidated computations can be re executed With more general combinations using place over however the offsets are computed by arbitrary Scheme code so that automatic re calculation is not generally possible Functional reac tive programming 3 might be the right solution to this problem and we intend to explore this possibility in future work Mean while Slideshow s current trade off flexible place over versus inflexible fonts has worked well in practice If a pict needs to be e608 mm ss E oO CIE define node name home wa Sgt Colon let ffontent nx Ankh Morpork vl append tux berwald Boi appena text Name roman 6 flcext name roman 10 Boi appena fftext Home roman 6 text home roman 10 cc superimpose rectangle 10 pict width fJontent 10 pict height Jontent Bentent define angua Frode ngua Uberwald define brutha ffnode Brutha Omnia define colon kode Sgt Colon Ankh Morpork define detritus oae Detritus Uberwald define others fJcloud 40 25 eoe aes A c define node name home let ontent vl append bbl append text N
5. a single slide to be a pict that is 1024x768 units The default border leaves a 984x728 region for slide content These units do not nec essarily correspond to pixels however Depending on the display at presentation time the pict is scaled e g by a factor of 25 32 for an 800x600 display If the display aspect is not 4 3 then scaling is limited by either the display s width or height to preserve the pict s original 4 3 aspect and unused screen space is painted black Slideshow does not use a special file format for slide presentations Instead a Slideshow presentation is a program and pict layouts are computed every time the presentation is started Consequently the target screen resolution is known at the time when slides are built This information can be used for example to scale bitmap images to match the display s pixels instead of units in the virtual 1024x768 space Information about the display is also useful for font selection 4 20 Fonts Fonts are not consistently available or even consistently named across operating systems To avoid platform dependencies Slideshow presentations typically rely on PLT Scheme s mapping of platform specific fonts through portable family symbols such as roman a serif font swiss a sans serif font usually Hel vetica modern a fixed width font and symbol a font with Greek characters and other symbols PLT Scheme users control the family to font mapping so a Sl
6. and slide title functions simply register a slide and programmers could build more elaborate abstractions in terms of these functions In practice programmers will prefer to use the more elaborate abstractions and part of Slideshow s job is to provide the most useful of such abstractions Thus Slideshow allocates the relatively short names slide slide title etc to functions that provide additional functionality The most simplest such addition is that each slide function takes any number of picts and it concatenates them with vc append us ing a separation of gap size which is 24 The slide function then ct superimposes the appended picts with a blank pict rep resenting the screen minus a small border The slide center function is like slide except that it centers the slide content with respect to the screen The slide title center accepts a title and also centers the slide slide title center Depth First Search scale graph 3 text An example graph swiss 32 Depth First Search Name Angua Name Sgt Colon Home Uberwald Home Ankh Morpork Name Brutha Home Omnia An example graph Name Detritus Home berwald The set of pre defined slide layouts includes only the layouts that we have found to be most useful Programmers can easily create other layouts by implementing functions that call slide 3 20 Managing Text In the spirit of providing short names for particula
7. might like hyperlinks on certain slides to start the demos Slideshow pro vides a clickback operator that takes a pict and a procedure of no arguments the result is a pict that displays like the given one but that also responds to mouse clicks by calling the pro cedure In this case we exploit the fact that slide generation and slide presentation execute on the same virtual machine Although many animations can be implemented as multiple slides that the speaker advances manually other animations should be entirely automatic Currently Slideshow provides only minimal support for such animations though an impera tive scroll transition function that registers a scroll ani mation over the previously registered slide This feature has been used mainly to animate an algebraic reduction making the expression movements easier to follow In the future the pict abstraction might be enriched to support more interesting kinds of animation 4 Rendering Slides Slideshow is designed to produce consistent results with any pro jector resolution as well as when generating PostScript versions of slides The main challenges for consistency concern pict scal ing and font selection as discussed in the following sections We also comment on Slideshow s ability to condense staged slides for printing and to pre render slides to minimize delays during a pre sentation 4 4 Scaling Since 1024x768 displays are most common Slideshow defines
8. minor improvements compared to the version 207 distribution paper and on slides A picture language alone is not enough how ever most of our effort behind Slideshow was in finding appropriate constructs for describing staging and rendering slides For further information on using Slideshow and for sample slide sets including slides for conference talks and slides for two courses see the following web page http www plt scheme org software slideshow 8 References 1 E Chailloux G Cousineau and A Su rez The MLgraph System 1997 2 J Clements M Felleisen R B Findler M Flatt and S Kr ishnamurthi Fostering little languages Dr Dobb s Journal pages 16 24 Mar 2004 3 C Elliott and P Hudak Functional reactive animation In Proc ACM International Conference on Functional Program ming pages 263 273 1997 4 R B Findler C Flanagan M Flatt S Krishnamurthi and M Felleisen DrScheme A pedagogic programming envi ronment for Scheme In Proc International Symposium on Programming Languages Implementations Logics and Pro grams pages 360 388 Sept 1997 5 S Finne and S Peyton Jones Pictures A simple structured graphics model In Proc Glasgow Functional Programming Workshop July 1995 6 P Henderson Functional geometry In Proc ACM Confer ence on Lisp and Functional Programming pages 179 187 1982 7 J D Hobby A user s manual for MetaPost Computer
9. of the graph we can use rectangle and cloud The rectangle and cloud functions take the height and width of the new pict rectangle 20 10 cloud 30 20 To label the boxes with the names of people we need picts for text The text function takes a string a font class and a font size and it produces a pict for the text text Angua roman 10 Angua To get a labeled box we need to combine a text pict with a rectangle pict The cc superimpose function stacks pictures on top of each other to create a new picture cc superimpose rectangle 50 20 text Angua roman 10 Angua The cc part of the name cc superimpose indicates that the picts are centered horizontally and vertically as they are stacked If in stead we want the label in the top left of the rectangle we can use lt superimpose 1t superimpose rectangle 50 20 Angua text Angua roman 10 To illustrate distances our boxes need to contain both a person s name and home We could put a name in the top left of a rectangle and the home in the bottom left but we d prefer to center both to gether The vl append function stacks picts vertically instead of on top of each other cc superimpose rectangle 50 30 vl append text Angua roman 10 Die text berwald roman 10 erwa The 1 in vl append means that the picts are left aligned as they are stacked We could right align the picts with vr append or cent
10. pic and MetaPost but like MLgraph etc Slideshow builds on a general purpose programming language so it can sup port modular development it allows programmers to write main tainable code libraries and tests and it is supported by a program ming environment MLgraph Pictures and FPIC provide a richer set of transformation operations mainly because they all build on PostScript while Slideshow provides a richer set of text formatting operations Also Slideshow s combination of find ghost and launder operations seems unique The primary difference between Slideshow and other functional picture languages though is that Slideshow has been refined through practice to meet the specific needs of slide creators In the IDEAL 13 picture language programmers define pic tures by describing constraints such as arrow X s endpoint is at tached to box Y s right edge In Slideshow the programmer ef fectively writes a constraint solver manually using functions like pict width ands find 1t We have opted for the more direct functional style instead of a constraint based language because we find that many patterns of constraints are easily covered by basic combinators such as v1 append and other patterns of constraints like adding lines to connecting node are easily abstracted into new functions Our choice of direct computation instead of using constraints af fects the kinds of properties that can be adjusted from outside
11. remedy to PowerPoint s lack of abstraction HTML s lack of flexibility and IATEX s lack of maintainability More generally we believe that the time is ripe for a functional approach to slide construction so we have reported on the constructs that we have found to work best Programmatic construction of pictures and slides is probably not for everyone even with powerful programming environment tools For various reasons many people will prefer to create pictures and slides in PowerPoint and without significant abstraction no matter how nice the language of picture construction For the authors tastes and purposes however programmatic con struction works well and we believe that it appeals to many pro grammers In our slides with proper code abstraction we can quickly experiment with different configurations of a picture add slide by slide animation and evolve ever more general libraries to use in constructing talks Many tasks can be automated entirely such as typesetting code and animating reduction sequences All of the figures in this paper are generated by Slideshow s pict library using exactly the code as shown In fact like many other picture languages Slideshow began as a system for generating fig ures for papers and the core pict language works equally well on We re defined the slide operations to produce boxed picts we scaled a few picts to save space and we used Slideshow ver sion 299 10 which includes
12. specifically support slide creation Figure 1 shows two screen dumps for one such tool The tool keeps track of picts that are generated during the run of a Slideshow pro gram and then allows a programmer to move the mouse over an in dividual expression to see the pict s generated the expression The black rectangles indicate mouseable positions In the first screen dump the mouse is over the content variable in node and on the right the four result pictures are shown one for each call to node when the program is executed In the second screen dump the mouse is over the rectangle call so four rectangles are shown to the right and the size of each rectangle matches the size of each corresponding content pict Moving the mouse over one of the calls to code would show a single pict which is the boxed content result of the call The cc superimpose call in code is in tail po sition To avoid turning loops into deep recursion our prototype tool ignores tail expressions Screen dumps for non textual slide syntax appear in Figure 2 The value for the nodes definition is expressed using a pict box as in dicated by the icon in the top right of the box For the first screen dump inside the pict box are five purple Scheme boxes as indi cated by the comma suggestive of unquote in the top right Each Scheme box escapes from pict mode back into Scheme The pro grammer created each Scheme box dragged it into place relative to other Schem
13. which takes horizontal and vertical displacements plus the size of the arrowhead and place it onto people let values ax ay find cb people angua bx by find ct people brutha place over people ax pict height people ay arrow line bx ax by ay 10 Name Angua Home berwald I Name Brutha Home Omnia Name Sgt Colon Home Ankh Morpork Name Detritus Home Uberwald Since we need to create many people we abstract the connection code Different connections will connect to different parts of of the source and destination people so our conn function accepts the relevant find procedures as arguments define conn main from find from to find to let values ax ay find from main from bx by find to main to place over main ax pict height main ay arrow line bx ax by ay 10 define graph letx p conn people people find lt angua find 1t p conn p angua find cb brutha find ct p conn p brutha find rt colon find 1b p conn p brutha find rc detritus find 1c p conn p detritus find ct colon find cb p conn p colon find rc others find 1c p Name Angua Name Sgt Colon Home Uberwald Home Ankh Morpork Ny Name Brutha ome Omia Name Detritus Home Uberwald 2 4 Colors and Line Widths The graph pict so far corresponds to the i
14. Slideshow Functional Presentations Robert Bruce Findler University of Chicago robby 2cs uchicago edu Abstract Among slide presentation systems the dominant application offers essentially no abstraction capability Slideshow an extension of PLT Scheme represents our effort over the last several years to build an abstraction friendly slide system We show how functional programming is well suited to the task of slide creation we re port on the programming abstractions that we have developed for slides and we describe our solutions to practical problems in ren dering slides We also describe a prototype extension to DrScheme that supports a mixture of programmatic and WYSIWYG slide cre ation Categories and Subject Descriptors H 4 1 Information Systems Applications Office Automation I 7 2 Document and Text Processing Document Preparation General Terms Languages 1 Abstraction Friendly Applications Strand a computer scientist at an airport and the poor soul would probably survive for days with only a network connected computer and five applications an e mail client a web browser a general purpose text editor a typesetting system and a slide presentation application More specifically while most any mail client or browser would satisfy the stranded scientist probably only Emacs or vi would do for editing IATEX for typesetting and Microsoft PowerPoint for preparing slides The typical business traveler
15. abstraction PowerPoint provides certain pre defined abstractions the background the default font and color etc but no ability to create new abstractions Among those who refuse to work without abstraction many retreat to a web browser because HTML is easy to generate programmat ically or the various extension of TEX plus a DVI PostScript PDF viewer Usually the results are not as aesthetically pleasing as PowerPoint slides and not as finely tuned to the problems of pro jecting images onto a screen Moreover novice users of TEX based systems tend to produce slides with far too many words and far too few pictures due to the text bias of their tool Meanwhile as a programming language TEX leaves much to be desired Slideshow a part of the PLT Scheme application suite 10 fills the gap left by abstraction poor slide presentation systems First and foremost Slideshow is an embedded DSL for picture generation but it also provides direct support for step wise animation bullet style text slide navigation image scaling to fit different display and projector types cross platform consistency Windows Mac OS and Unix X and PostScript output for ease of distribution Functional programming naturally supports the definition of picture combinators and it enables slide creators to create new abstractions that meet their specific needs In this paper we mainly demonstrate how Slideshow as a pro gramming language supports a
16. ackages IATEX remains well adapted for presenting math formulae and blocks of text but not for con structing pictures and not for implementing and maintaining ab stractions Like Slideshow Skribe 11 12 builds on Scheme to support doc ument creation but Skribe targets mainly the creation of articles books and web pages Since Skribe includes a IATEX output en gine it could be used to build slides through IATEX based packages by adding appropriate bindings Unlike Slideshow most slide presentation systems including all IATEX based PostScript based and PDF based systems treat the slide viewer as an external tool Separating the viewer from the slide generation language makes display specific customization more difficult and it inhibits the sort of integration with a program ming environment that we advocate An integrated viewer mean while can easily support executable code that is embedded within slides Embedded code is particularly useful in a presentation about programming or about a software system since an eval hyperlink can be inserted into any slide More generally Slideshow gives the presentation creator access to the complete PLT Scheme GUI tool box so practically anything is possible at presentation time 7 Conclusion In only the last few years laptop projected slides have become the standard vehicle for delivering talks and tools other than Power Point are still catching up We offer Slideshow as a
17. ame roman 6 text name roman 10 bbl append text Home roman 6 fjtext home roman 10 cc superimpose Geectengle 10 pict width Jfontent 10 pict height Jontent Bontent define angua Pode ngua Uberwald define brutha ffnode Brutha Omnia define colon Frode Sgt Colon Ankh Morpork define detritus pode Detritus Uberwald define others fJcloud 40 25 gt i Figure 1 Mousing over expressions to see resulting picts eoo nodes ss DrScheme oO eo nodes ss break define angua node Angua berwald define angua node Angua U berwald define brutha node Brutha Omnia define brutha node Brutha Omnia define colon node Sgt Colon Ankh Morpork define colon node Sgt Colon Ankh Morpork define detritus node Detritus berwald define detritus node Detritus Uberwald define others cloud 40 25 define others cloud 40 25 define nodes define nodes Figure 2 A pict box containing Scheme boxes parameterized by its font we simply use functional abstraction or parameterize Countless packages exist for describing slides with an HTML like notation Such packages typically concentrate on arranging text and pictures are imported from other sources Countless additional packages exists for creating slides with IATEX including foiltex and Prosper 14 With these p
18. bstraction but slide creators can also benefit from a measured dose of WYSIWYG slide construction WYSIWYG tools should be part of the slide language s program ming environment analogous to GUI builders for desktop appli cations We therefore report on experimental extensions of the DrScheme programming environment that support interactive slide construction along with language based abstraction Section 2 describes Slideshow s primitives for picture generation and Section 3 shows how we build on these operations to ad dress common slide construction tasks Section 4 briefly addresses practical issues for rendering slides on different media and op erating systems Section 5 describes our prototype extension of DrScheme 2 Picture Combinators A pict is the basic building block for pictures in Slideshow Roughly a pict consists of a bounding box and a procedure for drawing relative to the box Ultimately a slide is represented as a single pict to be drawn on the screen As a running example suppose that we wish to illustrate graph searching to novice programmers showing how a graph of people is traversed to find the name of a person who lives in a particular city The illustration will contain boxes labeled with names and lo cations directed connections among the boxes an arrow indicating the starting box and a cloud that stands in place of many unspeci fied boxes and connections 2 1 Pict Basics To create the basic elements
19. d drop adjust the top and bottom baselines e place over launder and ghost combination opera tors e find 1t sub pict finder All other pict operations can be implemented in terms of the above operations For historical reasons the actual primitives are less tidy than this set but Slideshow continues to evolve toward an im plementation with this set as the true primitives 3 From Pictures to Slides Picture construction primitives are half of the story for Slideshow The other half is a library of pict operations that support common slide tasks and that cooperate with a slide display system Com mon tasks include creating a slide with a title creating text with a default font breaking lines of text bulletizing lists and staging the content of a multi step slide Cooperating with the display system means correlating titles with a slide selection dialog and enabling clickable elements within interactive slides 3 Generating Slides Abstractly a slide presentation is a sequence of picts Thus a pre sentation could be represented as a list of picts and a Slideshow program could be any program that generates such a list We have opted instead for a more imperative design at the slide level a Slideshow program calls a slide function or variants of slide to register each individual slide s content slide scale graph 3 scale to fill the slide Name Angua Home berwald Name Brutha Home Omnia
20. e Omnia Name Detritus Home Uberwald 2 6 More Abstractions The graph example illustrates all of the properties of a pict it has a bounding box upper and lower baselines for text alignment sub pict locations and a drawing procedure In general a drawing ab straction may require additional properties and they can be imple mented as a new abstraction that encapsulates picts In particular instead of manually highlighting links to create graph2 and graph3 we would prefer to represent the figure as an actual graph of records and then implement depth first search to highlight certain links We therefore replace add lines with a graph definition and search function To implement the graph we first define record types for nodes and edges define struct node p edges define struct edge from find from to find to The declaration of node introduces the constructor make node and the selectors node p for the node s picture and node edges for the node s outgoing edges The declaration of edge similarly in troduces the constructor nake edge and selectors node from etc In addition to its start and end nodes an edge includes find from and find to fields for drawing the edge with hconn Using the new record constructors and PLT Scheme s shared ex tension of letrec we can define the graph of people define nodes shared i make node people list make edge i find lt a find 1t a make node angua
21. e boxes and then entered a Scheme expression into each box When the pict box is evaluated the expressions within Scheme boxes are evaluated to obtain sub picts and these sub picts are combined using the relative positions of Scheme boxes in the overall pict box Thus the pict box in the screen dump implements the node layout that we created with vr append and hc append in Section 2 2 and interactive placement seems more natural in this case than pro grammatic stacking For a full WYSTWYG treatment the program mer needs to see the pict results for each Scheme box rather than the Scheme code The second screen dump in Figure 2 shows the same tool and program in preview mode which uses results for the Scheme boxes from a recent execution to show a preview of the pict result The Sgt Colon box is highlighted because the pro grammer has just moved it using preview mode to pick a better arrangement These slide specific tools have yet to evolve beyond the experimen tal stage but they illustrate how a programming environment can provide WYSIWIG style tools that complement the language s ab straction capabilities 6 Slideshow Design and Related Work Slideshow s pict language is by no means the first language de signed for generating pictures and its picture constructors are sim ilar to those of Henderson s functional pictures 6 MLgraph 1 Pictures 5 FPIC 8 pic 9 MetaPost 7 and many other sys tems Unlike
22. e state components show up in the pict abstraction in terms of attribute defaults such as the draw ing color or width of a drawn line In particular the 1inewidth and colorize operators change the line width and color of a pict produced by triangle One further aspect of the drawing context that can be controlled externally is the drawing scale The scale operator scales a pict to make it bigger or smaller Inde pendent horizontal and vertical scales enable squashing and stretch ing as well Like color and line widths scaling is implemented by adjusting the scale of the underlying drawing context so that scale affects picts generated by dc as well as any other pict scale graph 0 4 0 2 M Although the underlying drawing context includes a current font as part of its state a pict s font cannot be changed externally unlike the pict s scale color or line width Changing a pict s font would mean changing the font of sub picts which would in turn would cause the bounding box of each sub pict to change in a complex way thus invalidating computations based on the sub pict boxes We discuss this design constraint further in Section 6 2 8 Pict Primitives Overall the following may be considered the primitives for Slideshow picts e dc the main constructor of picts e scale linewidth and colorize property adjusting op erations e inset lift and drop bounding box adjustments where lift an
23. ed hconn angua brutha M angua find cb brutha find ct hilite Name Brutha Home Omnia Finally we assemble the connection additions into a function and parameterize it over the highlighting function for each arrow By calling add lines with different arguments we can generate a sequence of pictures to use in a sequences of slides that illustrate how a search algorithm traverses links define add lines let p hconn ih abh bch bdh dch coh p find lt angua find lt ih P P p hconn p angua find cb brutha find ct abh p hconn p brutha find rt colon find lb bch p hconn p brutha find rc detritus find lc bdh p hconn p detritus find ct colon find cb dch p hconn p colon find rc others find lc coh p define graph2 add lines people hilite hilite dim dim dim dim define graph3 add lines people hilite hilite hilite dim dim dim nme Angua Hone berwald suc Brutha Hone Omnia sanc Sgt Colon Hone Ankh Morpork Name Detritus Home berwald Nume Sgt Colon Home Ankh Morpork one Name Detritus Home berwald 2 5 Functional Picts and Identity The colorize and linewidth operations are functional so they produce a new pict rather than modifying an existing pict The func tional nature of picts means that they can be used multiple times in constructing an image For example we can add a shadow to peo p
24. ed size of the rectangle It should grow to match the size of the labels plus a small amount of padding To create a pict whose size depends on another pict s size we can use pict width and pict height define person name home let content vl append hbl append text Name roman 6 text name roman 10 hbl append text Home roman 6 text home roman 10 cc superimpose rectangle 10 pict width content 10 pict height content content Name Angua define angua Home Uberwald person Angua Uberwald Name Brutha define brutha Home Omnia person Brutha Omnia At this point we can create several people plus the cloud and start ing arrow and combine them in a picture If we just use vc append and hc append to combine the people the layout will look too regular We can use inset to wrap varying extra space around some people the inset takes a pict and either one argument for an amount of space to add around the pict two arguments for separate horizontal and vertical space or four arguments for separate left top right and bottom space We can also use a blank pict to put extra space between the people define angua brutha vr append inset angua 10 10 10 O blank O 18 brutha define colon person Sgt Colon Ankh Morpork define detritus person Detritus berwald define others cloud 40 25 define people
25. er them with vc append If we want to prefix the boxed fields with Name and Home labels we can use hb append cc superimpose rectangle 80 30 vl append hb append text Name roman 10 text Angua roman 10 hb append Name Angua text Home roman 10 text berwald roman 10 Home Uberwald Naturally the b in hb append means that the picts are bottom aligned as they are stacked horizontally and hc append and ht append center and top align pictures In addition hbl append aligns text on baselines which is useful when picts contain text in different fonts or sizes cc superimpose rectangle 80 30 vl append hbl append text Name roman 6 text Angua roman 10 hbl append text Home roman 6 text berwald roman 10 Name Angua Home berwald More precisely hbl append aligns text using the bottom baseline in each pict in case one pict is a vertical combination of other text picts The ht1 append function aligns text using top baselines 2 2 Pict Abstractions Since we need to create several people in the graph we should ab stract the box construction into a function define person name home cc superimpose rectangle 80 30 vl append hbl append text Name roman 6 text name roman 10 hbl append text Home roman 6 text home roman 10 One obvious problem with this implementation is the hard wir
26. hc append angua brutha blank 20 0 inset vl append colon blank O 24 inset detritus 10 0 0 0 0 200 0 blank 20 0 others Name Angua A Name Sgt Colon Home Uberwald Home Ankh Morpork Name Brutha tne Omnia Name Detritus Home berwald 2 3 Finding Picts To add an arrow from Angua to Brutha we could insert an arrow pict into the vr append sequence but adding an arrow from Brutha to Sgt Colon is not so straightforward with stacking operations Slideshow provides a more general way to extend a pict which is based on finding the relative location of sub picts Each pict has an identity in the sense of Scheme s eq and all pict combining op erations preserve that identity internally To locate a sub pict within an aggregate pict Slideshow provides a family of operations begin ning with find The suffix of a find operation indicates which corner or edge of the sub pict to find it is a combination of 1 c or r i e left center or right with t t1 c or bl b i e top top baseline center bot tom baseline or bottom The results of a find operation are the coordinates of the found corner edge relative to the aggregate pict A find operation is often combined with place over which takes a pict horizontal and vertical offsets and a picture to place on top of the first pict For example we can create a connect ing arrow with arrow line
27. ide center scale add lines people hilite if after b hilite dim if after c hilite dim if after etc hilite dim if after etc hilite dim if after etc hilite dim 3 if after etc page para And so on page para Check cond Conly a Angua Conly b Brutha Conly c Sgt Colon ne Angus ee Sgt Colon tame berwald soe Ankh Morpork nee Angus ee Sgt Colon tame Oberwald hoe Ak Mo see Bra ee Bra ae Dette oen Jae Desine cs berwald Rcs berwald Check Angua Check Brulha AL Angus am Set Colon ee Angon ae Set Colon se Oberwald ce Anki Morpork am Oberwald n Ankh Morpork ao att sw Omnia oe Oberwald soma tell Check Sgt Colon And soon Much like text and hbl append for typesetting paragraphs with steps is too primitive for staging bullets or lines of text on a slide For example when posing a question to students an answer may be revealed only after the students have a chance to think about the question To support this simple kind of staging the slide function and all its variants treats the symbol next specially when it appears in the argument sequence All of the picts before next are first used to generate a slide and then the picts before next plus
28. ideshow programmer can assume that the user has selected reasonable fonts Alternately a program mer can always name a specific font though at the risk of making the presentation unportable Since specific fonts vary across platforms displays and users the specific layout of picts in a Slideshow presentation can vary due to different bounding boxes for text picts Nevertheless as long as a programmer uses pict width and pict height instead of hard wiring text sizes slides display correctly despite font varia tions This portability depends on computing pict layouts at display time instead of computing layouts in advance and distributing pre constructed picts Text scaling leads to additional challenges For many displays a font effectively exists only at certain sizes if a pict is scaled such that its actual font size would fall between existing sizes the un derlying display engine must substitute a slightly larger or smaller font Consequently a simple scaling of the bounding box in the 1024x768 space does not accurately reflect the size of the text as it is drawn leading to overlapping text or unattractive gaps To compensate for text scaling problems Slideshow determines the expected scaling of slides based on the current display size before generating picts It then uses the expected scale to gen erate a bounding box for text picts that will be accurate after scaling Occasionally the predicted scale is incorrect becau
29. le by creating a gray version that is behind and below the black version Name Angua Home berwald 1t superimpose inset colorize angua gray 3 3 0 0 angua In the resulting pict however a find operation for angua is am biguous it might find the black instance or it might find the gray instance The launder primitive takes a pict and produces one that is drawn the same its its input but with no find able sub picts By using launder we can provide a shadow for the graph without interfering with the way that connecting lines are drawn define add shadow p 1t superimpose inset colorize launder p gray Name Angua Home Uberwald 3300 p NX hconn add shadow angua brutha Name Brutha angua find cb brutha find ct Home Omnia hilite The complement of launder is ghost The ghost function creates a pict with the dimensions and sub pict locations of a given pict but with no drawing For example if we want just the arrows of the graph without the people we can ghost out the people This operation might be used for example to increase the default width of the arrow lines without affecting the default width of the person box lines 1t superimpose people linewidth 1 affects arrows not boxes add lines ghost people hilite hilite hilite dim dim dim Name Angua h Name Sgt Colon Home berwald Home Ankh Morpork Name Brutha Hom
30. mode Name Detritus Home berwald define graph3 search node edges nodes list colon graph line adder hilite Name Angua h Name Sgt Colon Home berwald Home Ankh Morpork Name Brutha nous Omnia Name Detritus Home berwald 2 7 Direct Drawing and Scaling Many pictures can be implemented purely with the functions de scribed so far For cases when the programmer wants direct access to the underlying drawing toolbox Slideshow provides a dc con structor where dc stands for drawing context The dc function takes an arbitrary drawing procedure and bounding box attributes When the pict must be rendered the drawing procedure is called with a target drawing context and offset For example a triangle pict constructor can be implemented us ing the primitive draw 1ine method of a drawing context define triangle w h dc lambda dest x y let mid x x w 2 far x x w far y y h send dest draw line x far y mid x y send dest draw line far x far y mid x y send dest draw line far x far y x far y w h 00 triangle 20 10 ZEN The primitive drawing context is highly stateful with attributes such as the current drawing color and drawing scale Not sur prisingly slides that are implemented by directly managing this state are prone to error which is why we have constructed the pict abstraction Nevertheless th
31. mplement any kind of staged slide where parts of the screen are revealed or modified in a sequence of slides In some cases a sequence of staged slides can be generated auto matically For example we can use slide center in a traversal with search to generate a sequence of slides that illustrates depth first search search node edges nodes list f graph compose lambda x slide center scale x 3 x line adder hilite En nuns lt E En thee berwald eee Ankh Morpork eee berwald thee Ankh Morpork cm rue cm rue E E tome berwald i Ankh Morpork Ne tome berwald ieee Ankh Morpork Ne o e E um Few slide sequences are so automatic however To facilitate man ual sequences Slideshow provides a with steps form that names each step in the sequence Expressions in the body of with steps can test whether the current step is before a particular step af ter a particular step or between two steps inclusive or exclusive to determine how to generate a slide For example we can use with steps to generate a slide sequence with commentary that is specific to our sample graph of people with steps a b c etc step names to use in the body sl
32. ndense mode and printing A skip slides function allows the programmer to increment the slide count directly 4 4 Pre rendering Slides To avoid screen flicker when advancing slides in an interactive pre sentation Slideshow renders each slide in an offscreen bitmap and then copies the bitmap to the screen The time required to render a slide is rarely noticeable but since a programmer can create arbitrary complex picts or write arbitrarily complex code that uses the drawing context directly the rendering delay for some slides can be noticeable To ensure instantaneous response in the common case Slideshow pre renders the next slide in the presentation sequence while the speaker dwells on the current slide If the speaker requests a slide change within half a second the slide is not pre rendered because the speaker may be stepping backward through slides 5 Environment Support Slideshow programs can be implemented using the DrScheme pro gramming environment 4 since Slideshow is an extension of PLT Scheme All of DrScheme s programming tools work as usual in cluding the on the fly syntax colorer the syntax checker the de bugger and the static analyzer Non textual syntax can be used in a Slideshow program such as a test case boxes comment boxes or XML boxes which support literal XML without concern for es cape characters 2 More importantly we can use DrScheme s extension interface to add new tools to DrScheme that
33. nitial slide in our demon stration To illustrate depth first search we need to highlight arrows in the picture as the algorithm traverses links We might implement this highlighting using the find operations re drawing arrows to add color More simply we can parameterize our existing code to add highlighting For example we can generalize conn to accept a highlighting dimming function that gives the arrow a color define hconn main from find from to find to hi dim let values ax ay find from main from bx by find to main to place over main ax pict height main ay hi dim arrow line bx ax by ay 10 define dim p colorize p gray define hilite p colorize p red Name Angua Home berwald hconn angua brutha angua find cb brutha find ct hilite Name Brutha Home Omnia In general a pict is constructed to use certain default attributes such as the width for lines and the color for drawing The colorize operation overrides the default color but it does not affect picts where the default is already overridden For arrows a color change is a good start but it does not ade quately highlight a thin arrow especially for readers of this paper who printed the colorized PS PDF on a black and white printer We can change hilite further to adjust the line width Name Angua defi hilit m define ilit p Home Uberwald linewidth 2 colorize p r
34. rly useful ab stractions Slideshow provides the function t for creating a text pict with a standard font and size which defaults to sans serif 32 units high Thus the label for the earlier example could have been im plemented as t An example graph instead of text An example graph swiss 32 The bt function is similar to t except that it makes the text bold and it makes its text italic For typesetting an entire sentence which might be too long to fit on a single line and might require multiple fonts Slideshow provides a para function The para function takes a width and a sequence of strings and picts and it arranges the text and picts as a paragraph that is bounded by the given width In the process para may break strings on word boundaries The page para function is like para but with a built in width that corresponds to the screen s width mi nus the margin slide title Depth First Search scale graph3 3 page para For bt depth first search follow a single branch at each node and backtrack only when a branch fails Depth First Search Name Angua A Name Sgt Colon Home Uberwald Home Ankh Morpork Name Brutha A Name Detritus Home Omnia i Home berwald For depth first search follow a single branch at each node and backtrack only when a branch fails The item function is similar to para except that it adds a bullet to the lef
35. science technical report AT amp T Bell Laboratories 1992 CSTR 162 8 S N Kamin and D Hyatt A special purpose languae for picture drawing In Proc USENIX Conference on Domain Specific Languages pages 297 310 Oct 1997 9 B W Kernighan PIC a graphics language for typesetting user manual Computer science technical report AT amp T Bell Laboratories 1991 CSTR 116 10 PLT PLT Scheme www plt scheme org 11 M Seranno and E Gallesio Skribe Home Page http www inria fr mimosa fp Skribe 12 M Seranno and E Gallesio This is Scribe In Proc Work shop on Scheme and Functional Programming pages 31 40 Oct 2002 13 C J Van Wyk IDEAL user s manual Computer science technical report AT amp T Bell Laboratories 1981 CSTR 103 14 T Van Zandt Prosper prosper sourceforge net
36. se the programmer uses the scale operation in addition to the implicit scale for the target display but this problem is rare When neces sary the programmer can correct the scale prediction by using the scale improve new text form and creating text picts within the dynamic extent of this form 4 3 Printing Slides A drawing context in PLT Scheme is either a bitmap display possi bly offscreen or a PostScript stream Thus printing a Slideshow presentation is as simple as rendering the slides to a PostScript drawing context instead of a bitmap context Slideshow provides a condense mode for collapsing staged slides Collapse mode automatically ignores next annotations a pro grammer can use next instead of next to force separate slides in condense mode In contrast alts annotations cannot be ig nored because each alternative can show different information A Slideshow programmer can indicate that intermediate alternatives should be skipped in condense mode by using alts instead of alts Slideshow synchronizes page numbering in condensed slides with slide numbering in a normal presentation In other words when slide skips a next annotation it also increments the slide num ber As a result a condense slide s number is actually a range indi cating the range of normal slides covered by the condensed slide Programmers can use the condense and printing predicates to further customize slide rendering for co
37. t of the paragraph In parallel to page para and para the page item function is like item but with a built in width that corresponds to the screen s width slide title Breadth First Search scale graph3 3 page para For bt breadth first search page item Check the immediate node page item If not found queue the node s neighbors and try the first node in the queue Breadth First Search Nave Angua A Nane Sgt Colon Home Uberwald Home Ankh Morpork Name Brutha Home Omnia Name Detritus Home Uberwald For breadth first search Check the immediate node If not found queue the node s neighbors and try the first node in the queue Note that given a bullet pict item is easily implemented in terms of para define item w picts htl append bullet blank gap size 2 0 apply para w pict width bullet gap size 2 picts Just as Slideshow provides many slide variants it also provides many para and item variants including variants for right justified or centered paragraphs and bulleted sub lists The page para function for example typesets a paragraph like page para but allows the result to be more narrow than the screen so that it gets centered 3 3 Staging Slides In Section 2 4 we showed how to abstract a pict constructing ex pression to support incremental changes to a pict This technique can be used to i
38. t to typeset a paragraph as italics we can use parameterize while constructing a pict with page parax slide center scale graph3 3 parameterize current main font italic swiss page para Remember links that we have traversed and don t follow them again later Nane Sgt Colon Home Ankh Morpork Nane Angua Hone Uberwald Name Detritus Home berwald Remember links that we have traversed and don t follow them again later Slideshow provides several other parameters to control slide de faults such as the current slide assembler parameter It con trols the overall style of a slide including the background and the layout of titles and it is typically set once per presentation 3 5 Display Interaction In addition to creating pictures for the screen slide presenters must sometimes interact more directly with the display system e A slide author might wish to attach a commentary to slides for the benefit of the speaker or for those viewing the slides after the talk Slideshow provides a comment constructor that takes a commentary string and produces an object that can be supplied to slide When the slide function finds a comment object it accumulates the comment into the slide s overall commentary instead of generating an image The Slideshow viewer displays a slide s commentary on demand in a separate window e For presentations that involve demos the speaker
39. the arguments after next are passed back into slide to generate more slides slide title Depth First Search scale graph3 3 colorize page para Colon in Ankh Morpork red next colorize page para Yes so we re done blue Depth First Search Depth First Search noe Angus M Set Colon ee Agua he Set Colon nm Oberwald i Ank Morpor a Oberwald n Ankh Morpork scs Bruha scs Bruha sor Omit oe Oberwald 2 S a Oberwald Colon in Ankh Morpork Colon in Ankh Morpork Yes so we re done Besides simple linear staging with next the slide function sup ports staging with alternatives that are later abandoned The alts symbol triggers this mode of staging The argument following alts must be a list of lists instead of a single pict Each of the lists is appended individually onto the preceding list of pict to gen erate a slide The final list is further appended onto the remaining arguments after the list of lists The next and alts symbols can be mixed freely slide title Breadth First Search scale graph2 3 page para From Brutha alts list list page item Try Detritus next page item No list page item Try Sgt Colon next page item Yes next page para So we find Sgt Colon in Ankh Morpork Breadth First Search Breadth First Search
40. would more likely insist on Microsoft Word for both text editing and typesetting In part computer scientists may prefer Emacs and IATEX because text editing has little to do with typesetting and these different tasks are best handled by different specialized applications More importantly tools such as Emacs vi and IATEX are programmable Through the power Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page To copy otherwise to republish to post on servers or to redistribute to lists requires prior specific permission and or a fee ICFP 04 September 19 21 2004 Snowbird Utah USA Copyright 2004 ACM 1 58113 905 5 04 0009 5 00 Matthew Flatt University of Utah mflatt cs utah edu of programming abstractions a skilled user of these tools becomes even more efficient and effective Shockingly many computer scientists give up the power of ab straction when faced with the task of preparing slides for a talk PowerPoint is famously easy to learn and use it produces results that are aesthetically pleasing to most audience members and it enables users to produce generic slides in minutes Like most GUI WYSIWYG oriented applications however PowerPoint does not lend itself easily to extension and
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