Patterns - special fills


Martin McBride, 2020-08-01
Tags pattern
Categories generativepy generative art

In generativepy, shapes can be filled or stroked (outline) using solid colours or patterns.

Currently, the only pattern supported is linear gradient. More patterns will be supported in future versions.

Patterns make use of the following classes, in the geometry module:

  • LinearGradient - defines a linear gradient.

Patterns all work in s similar way:

  • The pattern is first constructed using the constructor and any required builder methods.
  • The build method is then called to create the pattern.

The object returned by get_pattern can be used in place of a Color object when setting a stroke or fill.

See the patterns tutorial for examples.

LinearGradient

The LinearGradient class defines a linear gradient.

Constructor

LinearGradient()

Creates a LinearGradient object.

of_points

Sets the start and end points.

of_points(start, end)
Parameter Type Description
start (number, number) A tuple of two numbers, giving the (x, y) position of start point.
end (number, number) A tuple of two numbers, giving the (x, y) position of end point.

Specifies the start and end points of the gradient.

with_start_end

Sets the start and end colours.

with_start_end(start, end)
Parameter Type Description
start Color The first colour in the gradient.
end Color The second colour in the gradient.

Specifies the start and end colours of a simple two colour gradient.

This is a shortcut for

of_points([(0, start), (1, stop)])

A LinearGradient should always have either with_start_end or of_points, but not both.

with_stops

Sets a list of colour stops.

with_stops(stops)
Parameter Type Description
stops Sequence of stops A list or tuple of stops (see below)

Specifies individual stops in the gradient.

Each stop is a tuple of (position, color), where:

  • position is the position within the gradient (0 for start, 1 for end, 0.5 for halfway etc).
  • color is the colour at that stop.

For example [(0, Color('black')), (0.5, Color('red')), (1, Color('blue'))] goes from black to red to blue.

build

build()

Finalises the creation of the pattern. You must call this after all the construction steps, but before using the pattern.

get_pattern

get_pattern()

This method is used internally to get the Pycairo pattern object when the pattern is passed in to s Shape fill or stroke method.

You should not normally need to call this in your code.

If you found this article useful, you might be interested in the book Computer Graphics in Python or other books by the same author.

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