tensor_patch

#!/usr/bin/python3
#+
# Demonstration of effect of control points in a tensor-product patch.
#
# Copyright 2015 by Lawrence D'Oliveiro <ldo@geek-central.gen.nz>. This
# script is licensed CC0
# <https://creativecommons.org/publicdomain/zero/1.0/>; do with it
# what you will.
#-

import sys
import os
import qahirah as qah
from qahirah import \
    CAIRO, \
    Colour, \
    Matrix, \
    Rect, \
    Vector

colour1 = Colour.from_hsva((0.55, 0.7, 0.7))
colour2 = Colour.from_hsva((0.05, 0.7, 0.7))
offsets = (None, -1.0, -0.5, 0, 0.5, 1.0, 2.0)
  # offsets of patch control points from centre towards corners, None for default (Coons patch)
swatch_size = Vector(300, 300)
pix = qah.ImageSurface.create \
  (
    format = CAIRO.FORMAT_RGB24,
    dimensions = swatch_size * Vector(len(offsets), 1)
  )
g = qah.Context.create(pix)
for i, offset in enumerate(offsets) :
    pat = qah.MeshPattern.create()
    pat.begin_patch()
    for j, corner in \
        enumerate((
            Vector(0, 0),
            Vector(1, 0),
            Vector(1, 1),
            Vector(0, 1),
        )) \
    :
        pat.line_to(corner)
        pat.set_corner_colour(j, (colour1, colour2)[j % 2 == 0])
        if offset != None :
            pat.set_control_point(j, qah.interp(offset, Vector(0.5, 0.5), corner))
        #end if
    #end for
    pat.end_patch()
    pat.matrix = Matrix.scale(swatch_size).inv()
    g.matrix = Matrix.translate(Vector(swatch_size.x, 0) * i)
    g.source = pat
    g.new_path()
    g.rectangle(Rect.from_dimensions(swatch_size))
    g.fill()
#end for
pix.flush().write_to_png("%s.png" % os.path.basename(sys.argv[0]))