ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working with Pixel Bender shaders
When you create a Shader instance and link it to a Pixel Bender shader, a ShaderData object containing data about the
shader is created and stored in the Shader object’s data property. The ShaderData class doesn’t define any properties
of its own. However, at run time a property is dynamically added to the ShaderData object for each metadata value
defined in the shader source code. The name given to each property is the same as the name specified in the metadata.
For example, suppose the source code of a Pixel Bender shader includes the following metadata definition:
namespace : "Adobe::Example";
vendor : "Bob Jones";
version : 1;
description : "Creates a version of the specified image with the specified brightness.";
The ShaderData object created for that shader is created with the following properties and values:
namespace (String): "Adobe::Example"
vendor (String): "Bob Jones"
version (String): "1"
description (String): "Creates a version of the specified image with the specified brightness"
Because metadata properties are dynamically added to the ShaderData object, you can use a for..in loop to examine
the ShaderData object. Using this technique you can find out whether the shader has any metadata and what the
metadata values are. In addition to metadata properties, a ShaderData object can have properties representing inputs
and parameters that are defined in the shader. When you use a for..in loop to examine a ShaderData object, check
the data type of each property to determine whether the property is an input (a ShaderInput instance), a parameter (a
ShaderParameter instance), or a metadata value (a String instance). The following example shows how to use a
for..in loop to examine the dynamic properties of a shader’s data property. Each metadata value is added to a Vector
instance named metadata. Note that this example assumes a Shader instance named myShader is already created:
var shaderData:ShaderData = myShader.data;
var metadata:Vector. = new Vector.();
for (var prop:String in shaderData)
{
if (!(shaderData[prop] is ShaderInput) && !(shaderData[prop] is ShaderParameter))
{
metadata[metadata.length] = shaderData[prop];
}
}
// do something with the metadata
For a version of this example that also extracts shader inputs and parameters, see “Identifying shader inputs and
parameters” on page 305. For more information about input and parameter properties, see “Specifying shader input
and parameter values” on page 305.
Last updated 6/6/2012
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