[golang]svg图片默认按照左上角旋转，改为按中心旋转，重新计算中心偏移量

1 前言

svg图片默认按照左上角旋转，改为按中心旋转，重新计算中心偏移量

2 代码

type Point struct {
   X float64
   Y float64
}

func GetOffsetXYAfterRotationForSVG(W, H, L, T, Angle float64) (ret Point) {

   AngleRad := Angle * math.Pi / 180
   SinX := math.Sin(AngleRad)
   CosX := math.Cos(AngleRad)
   Z := math.Sqrt(math.Pow(W, 2)+math.Pow(H, 2)) / 2
   AngleRadBeta := math.Atan(H / W)
   AngleBeta := AngleRadBeta * 180 / math.Pi

   fmt.Println("Angle,SinX,CosX,H,W,L,T,ZHalf,AngleBeta=", Angle, SinX, CosX, H, W, L, T, Z, AngleBeta)

   translate := Point{L, T}

   //开始计算，在以对角线一半为半径画圆，初始化角度为Anglebeta
   Angle = Angle + AngleBeta
   p0 := Point{Z * math.Cos(AngleRadBeta), Z * math.Sin(AngleRadBeta)}
   //ShowPoint(p0)

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

   p1 := Point{Z * CosX, Z * SinX}
   //ShowPoint(p1)
   p1.Minus(p0)
   translate.Minus(p1)
   //ShowPoint(p1)
   fmt.Printf("p0=%+v,p1=%+v,p2=%+v", p0, p1, translate)
   fmt.Println()
   //保存精度
   translate.Decimal(3)
   ret = translate

   return

}

func DecimalPrec(value float64, prec int) float64 {
   value, _ = strconv.ParseFloat(fmt.Sprintf("%."+strconv.Itoa(prec)+"f", value), 64)
   return value
}

func (p1 *Point) Add(p0 Point) {

   p1.X = p1.X + p0.X
   p1.Y = p1.Y + p0.Y

   return
}

func (p1 *Point) Minus(p0 Point) {

   p1.X = p1.X - p0.X
   p1.Y = p1.Y - p0.Y

   return
}

func (p1 *Point) Times(scale float64) {

   p1.X = p1.X * scale
   p1.Y = p1.Y * scale

   return
}

func (p1 *Point) Decimal(prec int) {

   p1.X = DecimalPrec(p1.X, prec)
   p1.Y = DecimalPrec(p1.Y, prec)

   return
}

func ShowPoint(p0 Point) {
   fmt.Printf("point x=%v,y=%v", p0.X, p0.Y)
   fmt.Println()
}

3 输出

----start----
Angle,SinX,CosX,H,W,L,T,ZHalf,AngleBeta= 30 0.49999999999999994 0.8660254037844387 400 400 0 0 282.842712474619 45
p0={X:200.00000000000003 Y:200},p1={X:-126.7949192431123 Y:73.20508075688775},p2={X:126.7949192431123 Y:-73.20508075688775}
x,y= 126.795 , -73.205
----end----