Triangle_display

#Triangle_display  code by Ken Adams
#Triangle coordinates are entered in pixels. Then a turtle object is used to draw a triangle with fill color decided by
#the parameter 'col'. Then the perimeter and area are calculated. Results can be displayed in pixels or centimeters;
#to use centimeters the parameter 'cm' must be set to 1. Testing: four triangles were sketched by hand and area, perimeter
#calculated then their shape and calculations were confirmed using this program.

from turtle import Turtle

tina = Turtle() # time is a turtle object
pxcm = 0.026458333 # multiply pixels by this number to convert to centimeters

# calculates the distance on the plane between two coordinates
# will be called by the draw_triangle function
def line_length(x1,y1,x2,y2):
    length = ((x1-x2)**2 + (y1-y2)**2)**0.5
    return length

#draws a triagle with points (x1,y1), (x2,y2), (x3,y3)
def draw_triangle(t_name,x1,y1,x2,y2,x3,y3,col,cm): # if cm is set to 1 result will be in centimeters
    t_name.penup()# we dont want to trace the path from the origin to the starting point
    t_name.goto(x1,y1) # the first vertex of the triangle
    t_name.pendown() # ready to trace
    t_name.begin_fill()
    t_name.color(col)
    t_name.goto(x2,y2) # we trace from the first vertix to the second
    t_name.goto(x3,y3) # from the second to the third
    t_name.goto(x1,y1) #then back to the first
    t_name.end_fill()
    a = line_length(x1,y1,x2,y2) # we call another function to calculate the length of the side between the first two vertices
    b = line_length(x1,y1,x3,y3) # length second side
    c = line_length(x2,y2,x3,y3) # length third side
    #print("a = " +str(a) + "b = " +str(b) + "c = " +str(c))# code for testing
    perimeter = a + b + c # with known lengths we calculate the perimeter
    s= perimeter*0.5 # used later to calculate area
    area = (s*(s-a)*(s-b)*(s-c))**0.5 # well known formula for area


    if cm == 1: # dimensions were input and calculated in pixels. Here we have the option to convert to centimeters
        print("results in centimeters")
        perimeter = perimeter*pxcm
        area = area*pxcm*pxcm
        units = "centimeters" # the string 'units' will be printed as part of the output
    else:
        print("results in pixels")
        units = "pixels"
    xmean = (x1+x2+x3)/3
    ymean = (y1+y2+y3)/3
    t_name.penup()
    t_name.goto(xmean,ymean) # (xmean,ymean) should be somewhere in the middle of the triangle
    t_name.pendown()
    t_name.color("black")# new color for printing information on the triangle
    print_area =round(area,2) # we print results rounded to 2 dp
    print_perimeter =round(perimeter,2)
    t_name.write("Area: " + str(print_area) + " " + units + "\n\n")
    t_name.write("perimeter: " + str(print_perimeter) + " " + units)

    return perimeter, area
#draws the triangle and returns the perimeter and area
prim, area = draw_triangle(tina,-250,-275,-100,200,315,-275,"yellow",1) #example and first test
#prim, area = draw_triangle(tina,-275,-50,0,250,250,200,"yellow",1) # three more tests
#prim, area = draw_triangle(tina,50,200,-280,270,275,125,"yellow",1)
#prim, area = draw_triangle(tina,50,50,200,300,100,200,"yellow",1)

#prints the results in the python screen (not the Turtle screen)
print("perimeter " + str(prim) + "; area " + str(area))
print("bye")