Class Function

vispy/visuals/shaders/function.py:34–504

Representation of a GLSL function Objects of this class can be used for re-using and composing GLSL snippets. Each Function consists of a GLSL snippet in the form of a function. The code may have template variables that start with the dollar sign. These stubs can be replaced with ex

class Function(ShaderObject):
    """Representation of a GLSL function

    Objects of this class can be used for re-using and composing GLSL
    snippets. Each Function consists of a GLSL snippet in the form of
    a function. The code may have template variables that start with
    the dollar sign. These stubs can be replaced with expressions using
    the index operation. Expressions can be:

    * plain text that is inserted verbatim in the code
    * a Function object or a call to a funcion
    * a Variable (or Varying) object
    * float, int, tuple are automatically turned into a uniform Variable
    * a VertexBuffer is automatically turned into an attribute Variable

    All functions have implicit "$pre" and "$post" placeholders that may be
    used to insert code at the beginning and end of the function.

    Examples
    --------
    This example shows the basic usage of the Function class::

        vert_code_template = Function('''
            void main() {
            gl_Position = $pos;
            gl_Position.x += $xoffset;
            gl_Position.y += $yoffset;
        }''')

        scale_transform = Function('''
        vec4 transform_scale(vec4 pos){
            return pos * $scale;
        }''')

        # If you get the function from a snippet collection, always
        # create new Function objects to ensure they are 'fresh'.
        vert_code = Function(vert_code_template)
        trans1 = Function(scale_transform)
        trans2 = Function(scale_transform)  # trans2 != trans1

        # Three ways to assign to template variables:
        #
        # 1) Assign verbatim code
        vert_code['xoffset'] = '(3.0 / 3.1415)'

        # 2) Assign a value (this creates a new uniform or attribute)
        vert_code['yoffset'] = 5.0

        # 3) Assign a function call expression
        pos_var = Variable('attribute vec4 a_position')
        vert_code['pos'] = trans1(trans2(pos_var))

        # Transforms also need their variables set
        trans1['scale'] = 0.5
        trans2['scale'] = (1.0, 0.5, 1.0, 1.0)

        # You can actually change any code you want, but use this with care!
        vert_code.replace('gl_Position.y', 'gl_Position.z')