[golang]图片按中心旋转后，新图的左顶点位置的偏移量

func OffsetXYAfterRotationCore(W, H, L, T, Angle float64) (x, y float64) {

   var DX, DY, X, Y float64

   AngleRad := Angle * math.Pi / 180
   SinX := math.Sin(AngleRad)
   CosX := math.Cos(AngleRad)

   //0<=Angle <=90
   if Angle >= 0 && Angle <= 90 {
      DX = SinX * H
      DY = 0
      X = L - DX
      Y = T - DY
      //fmt.Println("At last Angle,X,Y,DX,DY=", Angle, X, Y, DX, DY)
   } else if Angle > 90 && Angle <= 180 {
      //90<=Angle <=180
      //SinX2 := math.Sin((180 - Angle) )
      //CosX2 := math.Cos((180 - Angle) )
      SinX2 := SinX
      CosX2 := -CosX
      DX = SinX2*H + W*CosX2
      DY = H * CosX2
      X = L - DX
      Y = T - DY
      //fmt.Println("At last Angle,X,Y,DX,DY=", Angle, X, Y, DX, DY)
   } else if Angle > 180 && Angle <= 270 {
      //SinX2 := math.Sin((270 - Angle))
      //CosX2 := math.Cos((270 - Angle))
      SinX2 := -CosX
      CosX2 := -SinX
      DX = SinX2 * W
      DY = CosX2*W + SinX2*H
      X = L - DX
      Y = T - DY
      //fmt.Println("At last Angle,X,Y,DX,DY=", Angle, X, Y, DX, DY)
   } else {
      //SinX2 := math.Sin((360 - Angle))
      SinX2 := -SinX

      DX = 0
      DY = SinX2 * W
      X = L - DX
      Y = T - DY
      //fmt.Println("At last Angle,X,Y,DX,DY=", Angle, X, Y, DX, DY)
   }

   x = X
   y = Y

   return
}