Leaders

Leader Properties

Show/Hide Leader Attributes

• im

  PIL image handle, link to the calling program

• at

  Coordinates on object

• angle

  Angle of first extension line, changes leader orientation

• extA

  Length inclined extension line, default 20

• extB

  Length horizontal extension line, default 20

• text

  Dimension text

• font

  Font of the text

• fill

  Line colour

• width

  Line width in pixels

• arrowhead

  Three integer tuple describing the shape and size of the arrow

• arrow

  position of the arrow on the line, which influences the direction it points.

Upper Leader		Lower Leader
Left position 225°	Right position 315°	Left position 135°	Right position 45°

Leaders allow us to refer to a specific item property not easily shown by normal dimensions or general decriptive notes.

The leader example has a single arrow on an angled line with a horizontal line over which the text is placed.

Changing the angle gives different leader orientations. It is better to use angles between 30 and 60° in each of the quadrants.

Show/Hide Code test_leader.py

from PIL import Image, ImageDraw, ImageFont
from DimLinesPIL import angled_text, dimension, polar2cart


def leader(im, dr, at, angle=315, extA=20, extB=20, width=1, arrowhead=(3,5,10),
            arrow='first', fill=(0,0,0), text=None, font=None):
    # leader to object, angle and length (extA) first part, then goes horizontal
    # for second part (extB). Only one arrow where leader points.
    # start at,

    #font = ImageFont.load_default() if font is None else font
    font = font if font else ImageFont.load_default()
    (wide, height) = font.getsize(text)

    h = height // 2

    if wide > extB:
        print('extB was increased from:',extB,'to accommodate the text',wide+10)
        extB = wide+10


    # dimension line
    phi = 180 if 90 < angle < 270 else 0
    ptB = polar2cart(at, angle, extA)
    ptC = polar2cart(ptB, phi, extB)
    dimension(dr, at, ptB, width=width, fill=fill, arrowhead=arrowhead,
              arrow=arrow)
    dr.line([ptB, ptC], width=width, fill=fill)

    # text position
    tp = ((ptB[0] + ptC[0])//2, ptB[1] - h - 5)

    angled_text(im, tp, text, 0, font, aall=0)

    #ldraw.text([at[0], at[1] +15], text=text, fill='black')

if __name__ == "__main__":
    Text = 'y+ε+m'

    Font = ImageFont.truetype('consola.ttf', 12)
    (wi, ht) = Font.getsize(Text)

    eb = wi + 10

    image2 = Image.new('RGB', (120, 120), '#FFFFDD')
    sdraw = ImageDraw.Draw(image2)

    lat = (60, 60)
    a = 315

    leader(image2, sdraw, lat, angle=a, extB=50, text=Text, font=Font)

    image2.show()
    #image2.save('../figures/leader'+str(a)+'.png')