Untitled

    def ccw(self, p):

        p1x,p1y,p2x,p2y,p3x,p3y = p ##basic math

        return (p2x - p1x)*(p3y - p1y) - (p2y - p1y)*(p3x - p1x)

 

    def Evaluate(self,event):

        blist = []## our list of points

        l= ly = lx = 0 ## our lowest x and y value and it's index in the list

        for x in range(self.Image.Width): ## loop through image

            for y in range(self.Image.Height):

                if self.Image.GetRed(x,y) == 0: ## if there's no red(should be black as there's only black and white)

                    if y > ly: lx, ly, l = x, y, len(blist)-1 ## if this y is lower(lower location on screen means higher value) then our current ly, make this our new ly

                    blist.append([x,y])## add it to the list

 

        for a in range(blist.count([lx,ly])): ## remove our lowest point

            blist.remove([lx,ly])

        N = len(blist) + 2 ## the lenght of our list when we can start the algorithm

        i = 0 ## current index

        for x,y in blist:

            ## a.b = |a||b|cos alpha, basic math

 

            blist[i] = [acos( (lx-x)/sqrt((lx-x)**2 + (ly-y)**2)),x,y]## the format of each element is [angle with lowest x and y, x, y]

            i = i + 1 ## our next index

        blist.sort() ## will sort or list by angle (first element of each element)

        blist.insert(0,[0,lx,ly]) ## insert our lowest x and y, would've thrown an devide by zero if we would calculate the angle.....

        blist.insert(0,blist[len(blist)-1])## our first element should be the same as our last

        blist = map(lambda x: x[1:],blist)## after sorting we only need our coordinates, so discard the angle element of each element

        M = 2 ## M has to be two

        for i in range(3, N):## loop through the list

            while self.ccw(blist[M-1] + blist[M] + blist[i]) <= 0:##while the three points are counterclockwise

                M = M - 1

            M += 1

            t = blist[i]## swam M and i

            blist[i] = blist[M]

            blist[M] = t

        blist = blist[:M]## we only need the list untill element M

        blist.append(blist[0])## to draw it we need our last and first element to be the same

        self.DrawHere.AddPoly(blist)

        self.DrawHere.UpdateDrawing()