ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working with Pixel Bender shaders
Specifying shader input and parameter values
Flash Player 10 and later, Adobe AIR 1.5 and later
Many Pixel Bender shaders are defined to use one or more input images that are used in the shader processing. For
example, it’s common for a shader to accept a source image and output that image with a particular effect applied to
it. Depending on how the shader is used the input value may be specified automatically or you may need to explicitly
provide a value. Similarly, many shaders specify parameters that are used to customize the output of the shader. You
must also explicitly set a value for each parameter before using the shader.
You use the Shader object’s data property to set shader inputs and parameters and to determine whether a particular
shader expects inputs or parameters. The data property is a ShaderData instance.
Identifying shader inputs and parameters
Flash Player 10 and later, Adobe AIR 1.5 and later
The first step in specifying shader input and parameter values is to find out whether the particular shader you’re using
expects any input images or parameters. Each Shader instance has a data property containing a ShaderData object. If
the shader defines any inputs or parameters, they are accessed as properties of that ShaderData object. The properties’
names match the names specified for the inputs and parameters in the shader source code. For example, if a shader
defines an input named src, the ShaderData object has a property named src representing that input. Each property
that represents an input is a ShaderInput instance, and each property that represents a parameter is a ShaderParameter
instance.
Ideally, the author of the shader provides documentation for the shader, indicating what input image values and
parameters the shader expects, what they represent, the appropriate values, and so forth.
However, if the shader isn’t documented (and you don’t have its source code) you can inspect the shader data to
identify the inputs and parameters. The properties representing inputs and parameters are dynamically added to the
ShaderData object. Consequently, you can use a for..in loop to examine the ShaderData object to find out whether
its associated shader defines any inputs or parameters. As described in “Accessing shader metadata” on page 303, any
metadata value defined for a shader is also accessed as a dynamic property added to the Shader.data property. When
you use this technique to identify shader inputs and parameters, check the data type of the dynamic properties. If a
property is a ShaderInput instance it represents an input. If it is a ShaderParameter instance it represents a parameter.
Otherwise, it is a metadata value. The following example shows how to use a for..in loop to examine the dynamic
properties of a shader’s data property. Each input (ShaderInput object) is added to a Vector instance named inputs.
Each parameter (ShaderParameter object) is added to a Vector instance named parameters. Finally, any metadata
properties are added to a Vector instance named metadata. Note that this example assumes a Shader instance named
myShader is already created:
Last updated 6/6/2012
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