We now combine both mammal and bird leg motions to create a sinister-looking spider. We also introduce a moving background for the first time. No transparent images are used here as the entire spider is made of animated vector lines and ovals.
Here, we need one long narrow strip image that is substantially wider than the Tkinter canvas provided. This not a problem and aids us in creating the illusion of a spider walking through an endless forest.
Execute the program shown as before.
# walker_spider_1.py
# >>>>>>>>>>>>>>>>
from Tkinter import *
import math
import time
root = Tk()
root.title("Mr Incy Wincy")
cw = 500 # canvas width
ch = 100 # canvas height
chart_1 = Canvas(root, width=cw, height=ch, background="white")
chart_1.grid(row=0, column=0)
cycle_period = 100 # time between new positions of thespider # (milliseconds).
base_x = 20
base_y = 100
avian = 1
ax = [ base_x, base_x+20, base_x+60 ]
ay = [ base_y, base_y, base_y ]
bx = [ base_x+90, base_x+130, base_x+170]
by = [ base_y, base_y, base_y ]
cx1 = base_x + 80
cy1 = base_y - 20
thy = 50
#=============================================
posn_x = 0
posn_y = 00
spider_backg = PhotoImage(file = "/constr/pics1/jungle_strip_1.gif")
mammal and bird leg motionscombining#===========================================
foot_lift = [10,10,5,-5,-10,-10] # 3 legs per side, each foot in # sequence = 18 moves
foot_stay = [ 0, 0,0, 0, 0, 0]
#========================================
# Given a line joining two points xy0 and xy1, the base of an # isosceles triangle,
# as well as the length of one side, "thy" this returns the # coordinates of
# the apex joining the equal-length sides - the position of the knee.
def kneePosition(x0, y0, x1, y1, thy, avian):
theta_1 = math.atan2((y1 - y0), (x1 - x0))
L1 = math.sqrt( (y1 - y0)**2 + (x1 - x0)**2)
if L1/2 < thy:
# The sign of alpha determines which way the knees bend.
if avian == 1:
alpha = -math.acos(L1/(2*thy)) # Avian
else:
alpha = math.acos(L1/(2*thy)) # Mammalian
else:
alpha = 0.0
theta_2 = alpha + theta_1
x_knee = x0 + thy * math.cos(theta_2)
y_knee = y0 + thy * math.sin(theta_2)
return x_knee, y_knee
def animdelay():
chart_1.update() # This refreshes the drawing on the # canvas.
chart_1.after(cycle_period) # This makes execution pause for 100 # milliseconds.
chart_1.delete(ALL) # This erases *almost* everything on # the canvas.
for j in range(0,11): # Number of steps to be taken - arbitrary.
mammal and bird leg motionscombiningposn_x -= 1
chart_1.create_image(posn_x,posn_y,anchor=NW, image=spider_backg)
for k in range(0,len(foot_lift)*3):
posn_x -= 1
chart_1.create_image(posn_x,posn_y,anchor=NW, image=spider_backg)
#cx1 += 3.5
cx1 += 2.6
# Phase 1
if k >= 0 and k <= 5:
ay[0] = base_y - 10 - foot_lift[k]
ax[0] += 8
by[0] = base_y - 10 - foot_lift[k]
bx[0] += 8
# Phase 2
if k > 5 and k <= 11:
ay[1] = base_y - 10 - foot_lift[k-6]
ax[1] += 8
by[1] = base_y - 10 - foot_lift[k-6]
bx[1] += 8
# Phase 3
if k > 11 and k <= 17:
ay[2] = base_y - 10 - foot_lift[k-12]
ax[2] += 8
by[2] = base_y - 10 - foot_lift[k-12]
bx[2] += 8
for i in range(0,3):
aknee_xy = kneePosition(ax[i], ay[i], cx1, cy1, thy, 1) # Mammal knee
bknee_xy = kneePosition(bx[i], by[i], cx1, cy1, thy, 0) # Bird knee
chart_1.create_line(ax[i], ay[i] ,aknee_xy[0], aknee_xy[1], width = 3)
chart_1.create_line(cx1, cy1 ,aknee_xy[0], aknee_xy[1], width = 3)
chart_1.create_line(bx[i], by[i] ,bknee_xy[0], bknee_xy[1], width = 3)
chart_1.create_line(cx1, cy1 ,bknee_xy[0], bknee_xy[1], width = 3)
chart_1.create_oval(cx1-15 ,cy1-10 ,cx1+15 , cy1+10, fill="black")
animdelay()
root.mainloop()
The essential art in making the spider walk acceptably is to adjust the length of stride, height of body above the ground, and thigh (leg segment) length to be consistent with each other. With slightly wrong adjustments, the legs roll over or appear made of very stretchy material.
There is also the issue of how the spider's leg movements should be synchronized. In this recipe, we have opted to make the limbs move in paired sequences.