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2ae16069d1
scripting engine fixes and cleanups, improved random generator in scripts, some documentation updates, tagged version 0.7.1 git-svn-id: svn://dyne.org/rastasoft/freej/freej@255 383723c8-4afa-0310-b8a8-b1afb83214fc
100 lines
3.8 KiB
Plaintext
100 lines
3.8 KiB
Plaintext
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FREEJ SCRIPT INTRODUCTION
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$Id$
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FreeJ is an asynchronous video rendering engine, it can be scripted
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using javascript syntax in an object oriented way, to control its
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operations thru a procedural list of commands and actions.
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This way we can start talking about "procedural video" as an evolution
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of the current non/linear paradigm widely spread in video production.
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Far from starting with such an high theoretical approach, this document
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aims to be a small and effective introduction to the first free software
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implementation of such a powerful functionality.
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It will not cover the programming syntax, but simply describe the
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objects that are made available to script FreeJ.
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Knowledge of generic object oriented programming syntax is suggested but
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not strictly necessary to make the first steps in the wonderful world of
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Procedural Video Scripting.
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Now let's get started!
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FreeJ scripting is completely object oriented, meaning that almost every
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operation is provided by objects that can be created: there are no global
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functions, but commands that are strictly related to a certain object.
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Layers and Effects are the object classes we can deal with. Once they
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exist, they will provide methods to control their operations.
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EXAMPLE:
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my_text_layer = new TxtLayer(); // create an new TxtLayer object (1)
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add_layer(my_text_layer); // make the new layer shown (2)
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my_text_layer.print("hello world!"); // print a message on the layer (3)
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In this example (1) we first create a new instance of the TxtLayer() class,
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which provides the Truetype rendering text layer; (2) then we add it to
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the list of layers processed by the engine; (3) at last we use the print()
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specific method to print something on the screen.
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Now try your first script by writing the three lines above in a file and
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then execute the file with 'freej -j myfile'
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there you are?
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then consider in *NIX systems you can use the interpreter header
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#!/usr/local/bin/freej -j
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at the beginning of your script, then by making it executable you'll have
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a self executing freej script!
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Generic and Specific methods:
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Every layer class inherits methods from the Layer superclass, providing
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generic methods common to all of them.
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Generic methods are available to change Layer attributes like: position,
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blit method, rotation, zoom, spin etc.
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Specific methods are found only on their layer, they can control special
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operations that a specific layer provides, like: printing a word on the
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text layer, appending a line to the scroll layer, skipping to a keyframe
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in a movie layer, etc.
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Here we go with a reference of all the methods made available by FreeJ:
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GENERIC METHODS common to all layers
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Layer.set_position(int x, int y) // coords of the upper left corner
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.set_blit("name") // must be an existing layer
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.set_blit_val(int val) // usually a value between 0 and 255
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.rotate(double val) // usually between 0 and 360
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.zoom(double x, double y) // floating point multiplier,
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// 1.0 means no zoom, 2.0 means double size
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.spin(double rotation, double zoom) // the layer will start rotating
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// and/or zooming (0 means stop)
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SPECIFIC LAYER TYPES:
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new CamLayer("/dev/video")
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new TextLayer("poetry.txt") (*)
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new MovieLayer("movie.avi")
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new ImageLayer("photo.png")
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new VScrollLayer("book.txt") (*)
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new ParticleLayer() // doesn't need a file
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(*) = the filename can be also omitted, the layer is then used with
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its own methods to feed the data to be processed.
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i.e. TxtLayer.print("string") or VScrollLayer.append("phrase")
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the constructor initialization consists of an open() on the file
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and it can return NULL in case of failure.
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In case the object returned is not NULL, it can be initialized using
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the init() call.
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...to be continued...
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see the script example in doc/freejscript-example.js
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