def GetTangentPoint(self, x, y, outx, outy):
"""
Get the tangent from an axternal point
args:
x,y is a point near the circle
xout,yout is a point far from the circle
return:
a tuple(x,y,x1,xy) that define the tangent line
"""
firstPoint = Point(x, y)
fromPoint = Point(outx, outy)
twoPointDistance = self.center.Dist(fromPoint)
if (twoPointDistance < self.radius):
return None, None
originPoint = Point(0.0, 0.0)
tanMod = math.sqrt(pow(twoPointDistance, 2) - pow(self.radius, 2))
tgAngle = math.asin(self.radius / twoPointDistance)
#Compute the x versor
xPoint = point.Point(1.0, 0.0)
xVector = Vector(originPoint, xPoint)
twoPointVector = Vector(fromPoint, self.center)
rightAngle = twoPointVector.Ang(xVector)
cx, cy = self.center.getCoords()
if (outy > cy): #stupid situation
rightAngle = -rightAngle
posAngle = rightAngle + tgAngle
negAngle = rightAngle - tgAngle
#Compute the Positive Tangent
xCord = math.cos(posAngle)
yCord = math.sin(posAngle)
dirPoint = Point(xCord, yCord) #Versor that point at the tangentPoint
ver = Vector(originPoint, dirPoint)
ver.Mult(tanMod)
tangVectorPoint = ver.Point()
posPoint = Point(tangVectorPoint + (outx, outy))
#Compute the Negative Tangent
xCord = math.cos(negAngle)
yCord = math.sin(negAngle)
dirPoint = Point(xCord, yCord) #Versor that point at the tangentPoint
ver = Vector(originPoint, dirPoint)
ver.Mult(tanMod)
tangVectorPoint = ver.Point()
negPoint = Point(tangVectorPoint + (outx, outy))
if firstPoint.Dist(posPoint) < firstPoint.Dist(negPoint):
return posPoint.getCoords()
else:
return negPoint.getCoords()
