Tutorial request: BezierPath() to pen

jo

Is there some example code on how to feed a BezierPath into a custom pen (where I manipulate the coordinates with a function and change the _lineTo) and then draw that transformed path in my canvas?

thanks, j

gferreira

hallo @jo,

here’s a quick example using FlattenPen:

from fontParts.fontshell import RGlyph
from fontPens.flattenPen import FlattenPen

# make a bezier shape (oval)
srcShape = BezierPath()
srcShape.oval(100, 100, 600, 600)

# draw bezier shape into a glyph
srcGlyph = RGlyph()
srcPen = srcGlyph.getPen()
srcShape.drawToPen(srcPen)

# flatten glyph into a new glyph
dstGlyph = RGlyph()
dstPen = dstGlyph.getPen()
flattenPen = FlattenPen(dstPen, approximateSegmentLength=200)
srcGlyph.draw(flattenPen)

# draw the result into a bezier shape
dstShape = BezierPath()
dstGlyph.draw(dstShape)
drawPath(dstShape)

maybe there are better ways to do it…

frederik

thanks Gustavo!

A BezierPath acts already like a pen or pointPen object and can be draw into a pen using path.drawToPen(anotherPen) or path.drawToPointPen(anotherPointPen)

see BezierPath.drawToPen

gferreira

@frederik thanks for the clarification. (polymorphism FTW!)

here’s a variation of the example script above, using BezierPaths directly as pens:

'''transform a bezier path using a pen'''

from fontPens.flattenPen import FlattenPen

# make a source shape
srcShape = BezierPath()
srcShape.oval(100, 100, 600, 600)

# make a new shape for the result
dstShape = BezierPath()

# get a flatten pen to draw the result
flattenPen = FlattenPen(dstShape, approximateSegmentLength=200)

# feed the source shape into the pen
srcShape.drawToPen(flattenPen)

# draw the resulting shape
drawPath(dstShape)

jo

thanks @gferreira and @frederik!
great help. i managed to botch my rough attempt at type on a curve.

# --------------------------------
#  imports 

from fontTools.pens.basePen import BasePen

# --------------------------------
#  settings 

pw = ph = 400
r = 89

angle = pi * 3.1
baseline = ph/2 + r

txt = 'HELLO'

tang_f = .333 # tangent factor
center = pw/2, baseline
focus  = pw/2, baseline - r

# --------------------------------
#  functions 

def ip(a, b, f): return a + (b-a) * f

def conv_point(p):

    x, y = p
    f = (x - pw/2) / (pw/2)
    a = -angle/2 * f
    x_conv = center[0] + cos(a + pi/2) * (r + y - baseline)
    y_conv = center[1] + sin(a + pi/2) * (r + y - baseline) - r
    return x_conv, y_conv

class convert_path_pen(BasePen):
    def __init__(self, targetPen):
        self.targetPen = targetPen
    def _moveTo(self, pt):
        self.targetPen.moveTo( conv_point(pt) )
        self.prev_pt = pt
    def _lineTo(self, pt):
        if self.prev_pt[0] == pt[0]:
            self.targetPen.lineTo( conv_point(pt) )
        else:
            tang_1 = ip(self.prev_pt[0], pt[0], tang_f), ip(self.prev_pt[1], pt[1], tang_f)
            tang_2 = ip(self.prev_pt[0], pt[0], 1-tang_f), ip(self.prev_pt[1], pt[1], 1-tang_f)
            self.targetPen.curveTo(conv_point(tang_1), conv_point(tang_2), conv_point(pt))
        self.prev_pt = pt
    def _curveToOne(self, tang_1, tang_2, pt):
        self.targetPen.curveTo(conv_point(tang_1), conv_point(tang_2), conv_point(pt))
        self.prev_pt = pt
    def _closePath(self):
        self.targetPen.closePath()

# --------------------------------
#  drawings 

path = BezierPath()
path.text(txt, font="Helvetica", fontSize = 80, align = 'center', offset=(0, baseline))

newPage(pw, ph)
trans_path = BezierPath()
trans_pen = convert_path_pen( trans_path )

path.drawToPen( trans_pen )
drawPath(trans_path)

obligatory gifs

frederik

looking good!!

gferreira

@jo this is very nice. thanks for sharing it!

frederik

found it back: this reminds me a thing I wrote some years ago