// RotateAround rotates the shape around the given point, by the given
// angle in degrees.
func (b *Base) RotateAround(x, y, angle float32) {
dx, dy := x-b.x, y-b.y
b.modelMatrix = mathgl.Translate3D(x, y, 0).Mul4(mathgl.HomogRotate3DZ(angle))
b.modelMatrix = b.modelMatrix.Mul4(mathgl.Translate3D(-dx, -dy, 0))
b.angle = angle
}
// Rotate rotates the shape around its center, by the given angle in
// degrees.
func (b *Base) Rotate(angle float32) {
b.modelMatrix = mathgl.Translate3D(b.x, b.y, 0).Mul4(mathgl.HomogRotate3DZ(angle))
b.angle = angle
}