How to write simple geometric shapes into numpy arrays

Question

I would like to generate a numpy array of 200x200 elements in size and put into it a circle centered into 100,100 coordinates, radius 80 and stroke width of 3 pixels. How to do

Answer 1

Cairo is a modern, flexible and fast 2D graphics library. It has Python bindings and allows creating "surfaces" based on NumPy arrays:

import numpy
import cairo
import math
data = numpy.zeros((200, 200, 4), dtype=numpy.uint8)
surface = cairo.ImageSurface.create_for_data(
    data, cairo.FORMAT_ARGB32, 200, 200)
cr = cairo.Context(surface)

# fill with solid white
cr.set_source_rgb(1.0, 1.0, 1.0)
cr.paint()

# draw red circle
cr.arc(100, 100, 80, 0, 2*math.pi)
cr.set_line_width(3)
cr.set_source_rgb(1.0, 0.0, 0.0)
cr.stroke()

# write output
print data[38:48, 38:48, 0]
surface.write_to_png("circle.png")

This code prints

[[255 255 255 255 255 255 255 255 132   1]
 [255 255 255 255 255 255 252 101   0   0]
 [255 255 255 255 255 251  89   0   0   0]
 [255 255 255 255 249  80   0   0   0  97]
 [255 255 255 246  70   0   0   0 116 254]
 [255 255 249  75   0   0   0 126 255 255]
 [255 252  85   0   0   0 128 255 255 255]
 [255 103   0   0   0 118 255 255 255 255]
 [135   0   0   0 111 255 255 255 255 255]
 [  1   0   0  97 254 255 255 255 255 255]]

showing some random fragment of the circle. It also creates this PNG: