# Polygon

Categories: generativepy generative art

The `Polygon`

class draws a polygon.

A polygon is defined by a list of points. The polygon is formed by joining the points with straight lines.

It is also possible to use bezier curves rather than straight lines to join the points. A shape can be formed from any combination of straight lines and curves.

There is also a `polygon`

function that just creates a polygon as a new path.

See the polygons tutorial for examples.

## Polygon class methods

The Polygon class inherits `add`

, `fill`

, `stroke`

, `fill_stroke`

, `path`

, `clip`

and other methods from Shape.

It has additional methods:

- of_points
- open

### of_points

Creates a polygon based on a list of points.

of_points(points)

Parameter | Type | Description |
---|---|---|

points | sequence of points | A sequence of line or curve specifiers. |

To define a simple polygon with straight sides, `points`

should just be a list of points, like this:

[(300, 100), (300, 150), (400, 200), (450, 100)]

This will create a polygon with 4 vertices, at the points (300, 100), (300, 150), (400, 200), and (450, 100).

Alternatively, it is possible to specify that some of the sides are bezier curves rather than straight lines, like this:

[(1, 4.5), (1, 2.5), (2, 3, 3, 4, 4, 2.5), (4, 4.5)]

In this case, the third item is 6 elements long. This means that the second and third points are connected by a bezier curve (rather than a straight line) with values:

(1, 2.5), (2, 3), (3, 4), (4, 2.5)

See the composite paths tutorial for more details.

The polygon will be closed by default. To create an open polygon, call the `open`

method.

### open

Creates an open polygon, rather than a closed polygon.

open()

Calling this method will cause the final polygon to be open - the last point will not be connected to the first point (see the example). To create a closed polygon, simply don't call this method.

## polygon function

Adds a polygon as a new path, without the need to create a `Polygon`

object in code.

polygon(ctx, points, closed=True)

Parameter | Type | Description |
---|---|---|

ctx | Context | The Pycairo Context to draw to |

points | list of (number, number) | A sequence of (x, y) tuples, giving the position of each vertex of the polygon. |

closed | boolean | Optional, set to `False` to create an open polygon |

## Example

Here is some example code that draws polygons using the class and the utility function. The full code can be found on github.

from generativepy.drawing import make_image, setup from generativepy.color import Color from generativepy.geometry import polygon, Polygon ''' Create polygons using the geometry module. ''' def draw(ctx, width, height, frame_no, frame_count): setup(ctx, width, height, width=500, background=Color(0.8)) # The polygon function is a convenience function that adds a polygon as a new path. # You can fill or stroke it as you wish. polygon(ctx, ((100, 100), (150, 50), (200, 150), (200, 200))) ctx.set_source_rgba(*Color(1, 0, 0)) ctx.fill() Polygon(ctx).of_points([(300, 100), (300, 150), (400, 200), (450, 100)]).open().stroke(Color('orange'), 10) make_image("/tmp/geometry-polygon.png", draw, 500, 500)

## See also

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