Circle
Martin McBride, 2020-08-23
Tags geometry circle arc sector segment
Categories generativepy generative art
The Circle class draws circles, arcs, sectors and segments.
There is also a circle function that just creates a circle as a new path.
Circle class methods
The Circle class inherits add, fill, stroke, fill_stroke, path, clip and other methods from Shape.
It has an additional method:
- of_center_radius
- as_arc
- as_sector
- as_segment
of_center_radius
Creates a circle based on the centre point and radius.
of_center_radius(center, radius)
| Parameter | Type | Description |
|---|---|---|
| center | (number, number) | A tuple of two numbers, giving the (x, y) position of the centre of the circle. |
| radius | number | A number, giving the radius of the circle. |
as_arc
Modifies a circle, to show only an arc. An arc is part of the circumference of the circle.
as_arc(start_angle, end_angle)
| Parameter | Type | Description |
|---|---|---|
| start_angle | number | A number, giving the start angle of the arc |
| end_angle | number | A number, giving the end angle of the arc |
This is used as a modifier with of_center_radius, to draw just an arc. To draw an arc use:
Circle(ctx).of_center_radius((0, 0), 1).as_arc(0, 1).stroke(Color('black'), 0.1)
Angles are measured in radians. Angle zero lies along the positive x-axis, and the angle increases in the clockwise direction - note that this is opposite to the normal mathematical convention, where angle increases in the counterclockwise direction. The difference is due to the fact that y increases as you move down the image in generativepy.
If you are using a flipped coordinate system (see the setup function in the drawing module), the angle increases in the counterclockwise direction.
Since an arc is a line, you should normally use the stroke method to draw it. If you attempt to fill the arc, it will fill it as if it was a segment.
as_segment
Modifies a circle, to show only a segment. An segment is the part of the circle that is cut off by a chord.
as_segment(start_angle, end_angle)
This function works in a similar way to the as_arc function, but it includes the area of the segment. You can fill or stroke the area, see the example below.
as_sector
Modifies a circle, to show only a sector. An sector is a "pizza slice", like you would use in a pie chart,.
as_sector(start_angle, end_angle)
This function works in a similar way to the as_arc function, but it includes the area of the sector. You can fill or stroke the area, see the example below.
circle function
Adds a circle as a new path, without the need to create a Circle object in code.
circle(ctx, center, radius)
| Parameter | Type | Description |
|---|---|---|
| ctx | Context | The Pycairo Context to draw to |
| center | (number, number) | A tuple of two numbers, giving the (x, y) position of the centre of the circle. |
| radius | number | A number, giving the radius of the circle. |
The circle function doesn't allow you to create arcs, segments or sectors.
Example
Here is some example code that draws circles 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 Circle, circle ''' Create circles using the geometry module. ''' def draw(ctx, width, height, frame_no, frame_count): setup(ctx, width, height, width=5, background=Color(0.8)) # The circle function is a convenience function that adds a circle as a new the path. # You can fill or stroke it as you wish. circle(ctx, (1, 1), 0.7) ctx.set_source_rgba(*Color(1, 0, 0)) ctx.fill() # Circle objects can be filled, stroked, filled and stroked. Circle(ctx).of_center_radius((2.5, 1), 0.7).fill_stroke(Color(0, 0, 1), Color(0), 0.05) Circle(ctx).of_center_radius((4, 1), 0.7).as_arc(0, 1).stroke(Color(0, 0.5, 0), 0.05) Circle(ctx).of_center_radius((1, 2.5), 0.7).as_sector(1, 3).stroke(Color('orange'), 0.05) Circle(ctx).of_center_radius((2.5, 2.5), 0.7).as_sector(2, 4.5).fill(Color('cadetblue')) Circle(ctx).of_center_radius((4, 2.5), 0.7).as_sector(2.5, 6).fill_stroke(Color('yellow'), Color('magenta'), 0.05) Circle(ctx).of_center_radius((1, 4), 0.7).as_segment(1, 3).stroke(Color('orange'), 0.05) Circle(ctx).of_center_radius((2.5, 4), 0.7).as_segment(2, 4.5).fill(Color('cadetblue')) Circle(ctx).of_center_radius((4, 4), 0.7).as_segment(2.5, 6).fill_stroke(Color('yellow'), Color('magenta'), 0.05) make_image("/tmp/geometry-circles.png", draw, 500, 500)
