ctypes example

draw.py

from ctypes import *
import sys

class Colour(Structure):
    _fields_ = [(c, c_uint8) for c in "rgb"]

foo = cdll.LoadLibrary('./image.so')

# foo.setup_image

foo.add_point.argtypes = (c_int, c_int, Colour)

foo.colour.argtypes = (c_uint8, c_uint8, c_uint8)
foo.colour.restype = Colour

# foo.write_image

foo.setup_image()

# We can define colours either using the C function or the above class
red = foo.colour(255, 0, 0)
blue = Colour(0, 0, 255)

for i in range(10, 50):
    for j in range(10, 50):
        if foo.add_point(i, j, red):
            print("Failed add point", file=sys.stderr)

for i in range(30, 70):
    for j in range(30, 70):
        if foo.add_point(i, j, blue):
            print("Failed add point", file=sys.stderr)

if foo.write_image():
    print("Failed to write image", file=sys.stderr)

image.c

#include <stdint.h>
#include <stdio.h>

struct colour {
	uint8_t r, g, b;
} image[80][80];

void
setup_image(void)
{
	for (int y = 0; y < 80; y++) {
		for (int x = 0; x < 80; x++) {
			image[x][y].r = 0;
			image[x][y].g = 0;
			image[x][y].b = 0;
		}
	}
}

int
add_point(int x, int y, struct colour p)
{
	if (x < 0 || x >= 80 || y < 0 || y >= 80)
		return 1;
	image[x][y] = p;
	return 0;
}

struct colour
colour(int r, int g, int b)
{
	return (struct colour){(uint8_t)r, (uint8_t)g, (uint8_t)b};
}

int
write_image(void)
{
	int r = 0 > printf("P3\n%d %d\n%d\n", 80, 80, 255);
	for (int y = 0; y < 80; y++) {
		for (int x = 0; x < 80; x++) {
			r |= 0 > printf("%d %d %d ",
				image[x][y].r,
				image[x][y].g,
				image[x][y].b);
		}
		printf("\n");
	}
	return r;
}

void
say_hello(int x)
{
	printf("Hello: %d\n", x);
}

Makefile

.PHONY: default
default: out.png

%.png: %.ppm
	convert $< $@

out.ppm: draw.py image.so
	python3 $< > $@

image.so: image.c
	$(CC) $(CFLAGS) $(LDFLAGS) -fPIC -shared -o $@ $<

.PHONY: clean
clean:
	rm -f image.so out.png out.ppm