grid.py

#!/usr/bin/python3

import os
import os.path
import math
import cairo

def draw_grid(ctx, cx, cy):
	ctx.set_source_rgba(0.0, 1.0, 1.0, 0.7)
	for u in range(0, int(cx) + 1, 5):
		ctx.move_to(u, 0)
		ctx.line_to(u, cy)
	for v in range(0, int(cy) + 1, 5):
		ctx.move_to(0, v)
		ctx.line_to(cx, v)
	ctx.stroke()
	ctx.set_source_rgba(0.0, 1.0, 1.0, 0.2)
	for u in range(int(cx) + 1):
		if u % 5 == 0:
			continue
		ctx.move_to(u, 0)
		ctx.line_to(u, cy)
	for v in range(int(cy) + 1):
		if v % 5 == 0:
			continue
		ctx.move_to(0, v)
		ctx.line_to(cx, v)
	ctx.stroke()

SIZE = 2048

for k, (bkg, dx, gx, dy, gy, fx, m) in enumerate([
		((.8, .0, .0), 0, (.0, .5, .0), 1, (.0, .0, .5), 1, (0, 1, 1, 0, 0, 0)),
		((.0, .5, .5), 1, (.0, .5, .0), 1, (.0, .0, .5), 0, (0, -1, -1, 0, SIZE, SIZE)),
		((.0, .8, .0), 1, (.5, .0, .0), 1, (.0, .0, .5), 0, (1, 0, 0, -1, 0, SIZE)),
		((.5, .0, .5), 0, (.5, .0, .0), 1, (.0, .0, .5), 1, (-1, 0, 0, 1, SIZE, 0)),
		((.0, .0, .8), 0, (.5, .0, .0), 1, (.0, .5, .0), 1, (-1, 0, 0, 1, SIZE, 0)),
		((.5, .5, .0), 1, (.5, .0, .0), 1, (.0, .5, .0), 0, (-1, 0, 0, 1, SIZE, 0)),
		]):
	surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, SIZE, SIZE)
	ctx = cairo.Context(surface)
	ctx.set_antialias(cairo.ANTIALIAS_NONE)
	ctx.set_source_rgba(*bkg, 1.0)
	ctx.paint()
	ctx.transform(cairo.Matrix(*m))

	ctx.save()
	ctx.scale(2048, 2048)
	ctx.set_operator(cairo.OPERATOR_ADD)

	pat = cairo.LinearGradient(0.0, 0.0, 1.0, 0.0)
	pat.add_color_stop_rgba(dx, *gx, 1)
	pat.add_color_stop_rgba(1 - dx, 0, 0, 0, 1)
	ctx.set_source(pat)
	ctx.paint()

	pat = cairo.LinearGradient(0.0, 0.0, 0.0, 1.0)
	pat.add_color_stop_rgba(1 - dy, *gy, 1)
	pat.add_color_stop_rgba(dy, 0, 0, 0, 1)
	ctx.set_source(pat)
	ctx.paint()

	ctx.restore()

	ctx.scale(102.4, 102.4)
	ctx.set_line_width(0.05)
	draw_grid(ctx, 20, 20)
	ctx.set_source_rgba(1.0, 1.0, 1.0, 1.0)
	ctx.move_to(10, 0)
	ctx.line_to(10, 20)
	ctx.move_to(0, 10)
	ctx.line_to(20, 10)
	ctx.stroke()
	ctx.select_font_face("DejaVu Sans", cairo.FONT_SLANT_NORMAL, cairo.FONT_WEIGHT_NORMAL)
	fo = cairo.FontOptions()
	fo.set_antialias(cairo.ANTIALIAS_NONE) # ANTIALIAS_GRAY doesn’t work for whatever reason
	ctx.set_font_options(fo)
	ctx.set_font_size(0.3)
	for u in range(20):
		x = u/10-1.0
		if fx:
			x = -x
		ctx.move_to(u + 0.1, 9.9)
		ctx.show_text(f'{x:.1f}')
	for v in range(20):
		if v == 10:
			continue
		ctx.move_to(10.1, 19.9 - v)
		ctx.show_text(f'{v/10-1.0:.1f}')

	os.chdir(os.path.dirname(__file__))
	surface.write_to_png(f'grid{k}.png')