Real Time Acrobat PDF Animation

Real Time Acrobat PDF Animation

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Description: Some simple JavaScript routines allow surprisingly fast and fancy (200x200, 20 frames per second) direct animation from within a PDF document. Demo shows a three phase power simulation.

Author: Don Lancaster (Fellow) | Visits: 2624 | Page Views: 2686
Domain:  High Tech Category: IT Subcategory: Computer Graphics 
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Real Time Acrobat Animation: A 3-Phase Power Simulation
Don Lancaster Synergetics, Box 809, Thatcher, AZ 85552 copyright c2005 as GuruGram #47 (928) 428-4073

A dobe's recent addition of JavaScript over Acrobat has dramatically upped the
animation possibilities done from totally within an Acrobat .PDF document. Obvious immediate uses are the not-previously-possible timed slideshows within a browser window, scroll and marquee effects, or flashing text in a PowerPoint Simulation. I was playing around with some simple Acrobat animation using JavaScript scripting and was utterly amazed at how fast and how large Acrobat animation can now be done. All at surprisingly low file sizes and rather simple program constructs. Ferinstance, nearly 20 frames per second seem possible on an older and sedate 850 MHz Pentium XP. While showing 200x200 pixel images. And needing only 8K or so per animation cell for storage. Before we go into some of the details, let's first click here to...


Yeah, I coulda built the demo into this GuruGram, but let's instead keep things brief and simple. What you are viewing here is a simulation of the electric field surrounding a three-phase power cable as it varies through each of its cycles. This is an expansion of the third example of our new Rebounding method of quickly and simply analyzing complex electromagnetic fields.

Getting Started
The key Adobe document needed is the Acrobat JavaScript Scripting Reference. This should be built into the help menu of your copy of Acrobat. Otherwise, you can click here for a copy of this and other JavaScript support docs. There are often five steps involved in Acrobat animation...
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Design an animated sequence. Build up the individual Cells. Assemble a continuing sequence. Single step the full sequence. Add user interactive control.

Your animated sequence could be either PostScript images or vector graphics and text. Or a mix of the two. Some browsers may be faster and better about glitchlessly displaying pure images, so images may end up better...

Always test your animation WITHIN a browser to avoid any rude surprises over glitches and continuity!

The third field plot example in REBOUND1.PDF clearly lent itself to a repeating sequence of 200 x 200 images that trace three phase power over one full cycle. Twenty-four cells of fifteen degrees of phase shift each seemed about right for the animated display. The more cells, the smoother the action, but the slower the maximum possible speed. The original field PostScript code can be modified for different phases by adding...

/phase 195 store

% set phase here

/calca {phase cos 500 mul 500 add} store /calcb {phase 120 add cos 500 mul 500 add} store /calcc {phase 240 add cos 500 mul 500 add} store

Field values of 1000 represent red and 0 represent blue. Procs calca, calcb, and calcc can be used to find the appropriate boundary value color for each of the three conductors in your current cell as a function of the desired phase angle. After you have created all of your cells, combine them in one Acrobat document. Then test them by using the front and back arrows. Then add this crucial detail...

When assembling your cells into a complete sequence, DUPLICATE YOUR FIRST CELL to provide a good place to initialize JavaScript variable definitions and such.

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When closing your animation loop, always return to the SECOND cell, not the first one. Remember that internal Acrobat page numbering always starts with page ZERO.

JavaScript and PostScript complement themselves in many ways. PostScript is a far more powerful and more intuitive general purpose computing language, while JavaScript excels at interactive user control. Two of the many places where JavaScript actions can be added to an Acrobat document are on page start and on mouse action. Any page start JavaScript command is entered by going to Document and then Set Page Action. A mouse action for a field such as a button is entered by clicking on the Form Tool, right clicking on the button, then followed by Properties. JavaScript variables must be initialized before they can be used. If a variable is to be used on all the pages of an Acrobat display, it must have a name similar to global.zorch. Once you figure out all of the arcane rules, the final JavaScript code can be surprisingly compact and simple. Here is some possible JavaScript initialization code for the first document page of our simulation...

global.animate = false ; global.speed = 4 ; this.pageNum++ ;

Our first line defines a flag that determines whether the animation will stop or run. This is important because...

Continuous animation will hang your program! ALWAYS provide user exit stop buttons or timouts!

The second line is an optional time delay that can be added to each cell. The integer is in milliseconds Normally, you are processor limited and want to run as fast as possible. But additional time delay can provide user interaction or reduce the variations with CPU speed. In other uses, a app.setTimeOut variable of 1300 might give a 1.3 second display for a chosen slide show cell. Unlike the original full screen slide shows, you can have fractional second values and do your show from within a web browser.
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The third line moves you unconditionally to the next cell. Thus, on entry or when the user clicks on the "go to beginning" arrow, needed JavaScript values are initialized, followed by a jump to the start of the actual animated sequence.

Cell Sequencing
Here's some page entry code to move you to the next cell in the sequence...

bbb = app.setTimeOut ("if (global.animate){this.pageNum++}", global.stall) ; bbb ;

This defines a local bbb variable that says "Delay for the global.stall time, then check to see if the global.animate flag will let us animate. If so, move to the next cell at the end of the stall time." The very last cell in the sequence is slightly different because it has to return to the beginning of the live cells to be displayed...

bbb = app.setTimeOut ("if (global.animate){this.pageNum = 1}", global.stall) ; bbb ;

Note that this.pageNum = 1 goes to the second cell in the sequence. Because internal page numbering starts at zero. We thus bypass the initialization cell on repeated cycles. Note also that Adobe uses an app.setTimeOut variable that differs from the normal JavaScript setTimeout by its case sensitivity. Capital "O", not "o".

User Interaction
Three step, stop, and run field buttons are used to provide a user interface. Here is the JavaScript step code for an internal cell...

this.pageNum++ ;

And for the last cell...
this.pageNum = 1 ;

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The stop button JavaScript coding is the same for all cells...

global.animate = false ;

A pair of codings is needed for our run buttons. This for internal cells...

global.animate = true ; if (global.animate){this.pageNum++} ;

And this one to close the loop for the next cycle...

global.animate = true ; if (global.animate){this.pageNum = 1} ;

Some additional tips: Debugging can be eased with temporary alert boxes, perhaps done as...

zzz = app.alert ("hi there",0) zzz

Variables can be inserted into the alert message text string and inspected. A similarly done yyy = app.beep(4) ; can also be used to place one of four system beeps at any cell during debugging. For some strange reason, the right and left arrows will be much slower (and a lot more glitchy) at moving between your Acrobat pages than the this.pageNum++ or a this.pageNum = 1 JavaScript commands. Always check "live" in a browser to make sure your page content will appear fast enough for effective, fast, and totally glitch-free animation.

For More Help
Enhancements and improvements on this fast, convenient, and super flexible .PDF animator can be made available to you on a Custom Consulting basis. Additional GuruGrams are found here, PostScript topics here, and Acrobat info here. Further GuruGrams await your ongoing support as a Synergetics Partner.
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