Pseudo shaders in Python

The file ShaderLib.py can be imported - It contains the following classes

• BaseShader
• BaseImage - Inherits from BaseShader
• MultiThreadedShader - Inherits from BaseShader
• LayerShader - Inherits from BaseShader
• NumExprLayerShader - Inherits from BaseShader

BaseShader

The BaseShader has little function and should not be used.

However its methods are used throughout.

Construction

Arguments:

• Width
• Height

saveImage(filename)

Method to save a shader's image to file locally.
Arguments:

• Filename: A string relating to the where the file will be saved. Uses PIL.

getPixel(u, v)

Method to get the colour information of an individual pixel. Returns an numpy.ndarray.

Arguments:

• u: Float relating to X position in image (0 to 1)
• v: Float relating to Y position in image (0 to 1)

BaseImage

Used to load images from file into a format that can be processed

Construction

Arguments:

• filename

MultiThreadedShader

Construction

See base shader

Arguments:

• Threads: The total number of threads used when executing this shader.

runShader(shaderProgram)

Runs the specified program on the shader's image.

Example:

def shader(arguments):
    u, v = arguments
    # u, v: the relative position of the pixel (x/width, y/height) in the image. Float between 0 and 1.
    e = np.uint8(v * 255)
    # Output must be a np.array consisting of np.uint8 - 0 to 255. RGBA format.
    return np.array([e, e, e, 255])

This method is multithreaded.

LayerShader

Construction

See base shader

addSubShader(shaderID, shader, shaderProgram)

Used to add layers to a LayerShader.
The shader will be run when added - There is no need to run it first.
Arguments:

• shaderID: A string identifying this layer.
• shader: A class descended from BaseShader
• shaderProgram: The program to be run on the layer.

putShader(shaderID, shader)

Used like addSubShader, however the shader will not be run when added.
Arguments:

• shaderID: A string identifying this layer.
• shader: A class descended from BaseShader

runShader(masterShader)

Used to run a shader which has access to the layers added to the shader.
Arguments:

• masterShader: A shader which has access to all layers of the current LayerShader
  An example of a "master program":

def masterShader(u, v, ls):
    # Currently collapsed arguments are not needed.
    # u, v: Same as base ShaderProcess
    # ls: A dictionary relating ShaderID with sub shaders
    e = ls["sh1"].getPixel(u, v)[0] * (1-u) * v ** 2
    # ls["sh1"] retrieves the subProcess with ID "sh1"
    return np.array([e, e, e, 255])

NumExprLayerShader

Construction

See base shade

runShader

This method can be used to run a NumExpr epression which operates on the whole image array. - So it's similar to the LayerShader, but can, with optimisation, be more efficient.
NumExpr does not support dictionaries or any sort of indexing, in order to run an expression on this object, you must first define properties on this object of the image property from the image/shader you wish to use.

Example:

nelsh = NumExprLayerShader(512, 512)

nelsh.sh1 = sh1.image
nelsh.sh2 = sh2.image

nelsh.runShader("sh1 * 0.1 + sh2 * 0.9")

Where sh1 and sh2 are implementations of the BaseShader class.

For more information, visit the NumExpr 2.0 User Guide