Drawbot output for responsive lettering UFO

responsive_drawbot_animated.py

#
# script for drawbot extension in robofont
# draws a fitted / interpolating image from a responsive lettering ufo
# erik@letterror.com / 20231204

def ip(a, b, f):
    return a + f * (b-a)
    
page = (659, 500)    # image size
margin = 59    # nice to have a margin

f = CurrentFont()

nt = f["narrow-thin"].toMathGlyph()
wt = f["wide-thin"].toMathGlyph()
nb = f["narrow-bold"].toMathGlyph()
wb = f["wide-bold"].toMathGlyph()

# get the ratios
ntBounds = f["narrow-thin"].getLayer("bounds").bounds
wtBounds = f["wide-thin"].getLayer("bounds").bounds
nbBounds = f["narrow-bold"].getLayer("bounds").bounds
wbBounds = f["wide-bold"].getLayer("bounds").bounds

# get the bounds
xMin, yMin, xMax, yMax = ntBounds
narrowX = xMax-xMin
narrowY = yMax-yMin
xMin, yMin, xMax, yMax = wtBounds
wideX = xMax-xMin
wideY = yMax-yMin


f = CurrentFont()

names = ["narrow-thin", "wide-thin", "narrow-bold", "wide-bold"]

# what width and height are we aiming for
wantWidth = page[0]-2*margin
wantHeight = page[1]-2*margin
wantRatio = wantWidth / wantHeight
wantScale = wantHeight / narrowY

# have a responsive lettering ufo open as current font
# make sure we have the names we need for this to work
for n in names:
    assert n in f

# this is how to find the widthFactor from the known parameters:
# ---
#wantRatio = (narrowX + widthFactor*(wideX-narrowX)) / narrowY
#wantRatio * narrowY = narrowX + widthFactor*(wideX-narrowX)
#(wantRatio * narrowY) - narrowX = widthFactor*(wideX-narrowX)
#((wantRatio * narrowY) - narrowX) / (wideX-narrowX) = widthFactor
# ---

widthFactor = ((wantRatio * narrowY) - narrowX) / (wideX-narrowX)

# these are the fitted thin and bold masters
w1 = ip(nt, wt, widthFactor)
w2 = ip(nb, wb, widthFactor)

weightFactor = 0.4
steps = 10

for s in range(steps+1):
    newPage(*page)
    weightFactor = s/steps

    # draw the steps
    with savedState():
        fill(.4,1,0)
        stroke(None)
        translate(margin, margin)
        scale(wantScale)
        translate(0,-f.info.descender)
        # this is how to calculate the weightfactor
        w3 = ip(w1, w2, weightFactor)
        drawGlyph(w3)

saveImage(f"{f.info.familyName}_{steps}.gif")