Adobe
Pixel Bender is a programming language that is used to create or
manipulate image content. Using Pixel Bender you create a kernel,
also known as a shader. The shader defines a single function that
executes on each of the pixels of an image individually. The result
of each call to the function is the output color at that pixel coordinate
in the image. Input images and parameter values can be specified
to customize the operation. In a single execution of a shader, input
and parameter values are constant. The only thing that varies is
the coordinate of the pixel whose color is the result of the function
call.
Where possible, the shader function is called for multiple output
pixel coordinates in parallel. This improves shader performance
and can provide high-performance processing.
In ActionScript, three types of effects can be easily created
using a shader:
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drawing fill
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blend mode
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filter
A shader can also be executed in stand-alone mode. Using stand-alone
mode a shader’s result is accessed directly rather than pre-specifying
its intended use. The result can be accessed as image data or as
binary or number data. The data need not be image data at all. In
this way you can give a shader a set of data as an input. The shader
processes the data, and you can access the result data returned by
the shader.
Pixel Bender support is available starting in Flash Player 10
and Adobe AIR 1.5. Pixel Bender blends, filters, and fills are not
supported under GPU rendering. On mobile devices, Pixel Bender shaders
do run under CPU rendering. However, performance is not at the same
level as on a desktop computer. Many shader programs may only execute
at a few frames per second.
Important concepts and terms
The following
reference list contains important terms that you will encounter when
creating and using Pixel Bender shaders:
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Kernel
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For Pixel Bender, a kernel is the same thing as a shader.
Using Pixel Bender your code defines a kernel, which defines a single
function that executes on each of the pixels of an image individually.
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Pixel Bender bytecode
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When a Pixel Bender kernel is compiled it is transformed
into Pixel Bender bytecode. The bytecode is accessed and executed
at run time.
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Pixel Bender language
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The programming language used to create a Pixel Bender kernel.
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Pixel Bender Toolkit
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The application that is used to create a Pixel Bender bytecode
file from Pixel Bender source code. The toolkit allows you to write,
test, and compile Pixel Bender source code.
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Shader
-
For the purposes of this document, a shader is a set of functionality written
in the Pixel Bender language. A shader’s code creates a visual effect
or performs a calculation. In either case, the shader returns a
set of data (usually the pixels of an image). The shader performs
the same operation on each data point, with the only difference
being the coordinates of the output pixel.The shader is not written
in ActionScript. It is written in the Pixel Bender language and compiled
into Pixel Bender bytecode. It can be embedded into a SWF file at compile
time or loaded as an external file at run time. In either case it
is accessed in ActionScript by creating a Shader object and linking
that object to the shader bytecode.
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Shader input
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A complex input, usually bitmap image data, that is provided
to a shader to use in its calculations. For each input variable
defined in a shader, a single value (that is, a single image or
set of binary data) is used for the entire execution of the shader.
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Shader parameter
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A single value (or limited set of values) that is provided
to a shader to use in its calculations. Each parameter value is
defined for a single shader execution, and the same value is used
throughout the shader execution.
Working through the code examples
You
may want to test the example code listings that are provided. Testing
the code involves running the code and viewing the results in the
SWF that’s created. All the examples create content using the drawing
API which uses or is modified by the shader effect.
Most of the example code listings include
two parts. One part is the Pixel Bender source code for the shader
used in the example. You must first use the Pixel Bender Toolkit
to compile the source code to a Pixel Bender bytecode file. Follow these
steps to create the Pixel Bender bytecode file:
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Open
Adobe Pixel Bender Toolkit. If necessary, from the Build menu choose “Turn
on Flash Player warnings and errors.”
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Copy the Pixel Bender code listing and paste it into the
code editor pane of the Pixel Bender Toolkit.
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From the File menu, choose “Export kernel filter for Flash
Player.”
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Save the Pixel Bender bytecode file in the same directory
as the Flash document. The file’s name should match the name specified
in the example description.
The
ActionScript part of each example is written as a class file. To
test the example in Flash Professional:
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Create an empty Flash document and save it to your computer.
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Create a new ActionScript file and save it in the same directory
as the Flash document. The file’s name should match the name of
the class in the code listing. For instance, if the code listing
defines a class named MyApplication, use the name MyApplication.as
to save the ActionScript file.
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Copy the code listing into the ActionScript file and save
the file.
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In the Flash document, click a blank part of the Stage or
work space to activate the document Property inspector.
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In the Property inspector, in the Document Class field, enter
the name of the ActionScript class you copied from the text.
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Run the program using Control > Test Movie
You will
see the results of the example in the preview window.
These techniques for testing example code
listings are explained in more detail in
How to Use ActionScript Examples
.
