def preShear(self, h, v):
        """Calculate pre shearing and replace current matrix."""
        a, b = self.a, self.b
        self.a += v * self.c
        self.b += v * self.d
        self.c += h * a
        self.d += h * b
        return self
def preShear ( self , h , v ) : a , b = self . a , self . b self . a += v * self . c self . b += v * self . d self . c += h * a self . d += h * b return self
Calculate pre shearing and replace current matrix.