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Accessing shader metadata

While creating a Pixel Bender shader kernel, the author can specify metadata about the shader in the Pixel Bender source code. While using a shader in ActionScript, you can examine the shader and extract its metadata.

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.<String> = new Vector.<String>();

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. For more information about input and parameter properties, see Specifying shader input and parameter values.