code: func (g *GeoM) SetElement(i, j int, element float64) {
  	e := float32(element)
  	switch {
  	case i == 0 && j == 0:
  		g.a_1 = e - 1
  	case i == 0 && j == 1:
  		g.b = e
  	case i == 0 && j == 2:
  		g.tx = e
  	case i == 1 && j == 0:
  		g.c = e
  	case i == 1 && j == 1:
  		g.d_1 = e - 1
  	case i == 1 && j == 2:
  		g.ty = e
  	default:
  		panic("ebiten: i or j is out of index")
  	}
  }
docs: // SetElement sets an element at (i, j).