internal/affine/colorm.go
func (c *ColorM) Concat(other *ColorM) *ColorM {
	if !c.isInited() {
		return other
	}
	if !other.isInited() {
		return c
	}

	lhsb := colorMIdentityBody
	lhst := colorMIdentityTranslate
	rhsb := colorMIdentityBody
	rhst := colorMIdentityTranslate
	if other.isInited() {
		if other.body != nil {
			lhsb = other.body
		}
		if other.translate != nil {
			lhst = other.translate
		}
	}
	if c.isInited() {
		if c.body != nil {
			rhsb = c.body
		}
		if c.translate != nil {
			rhst = c.translate
		}
	}

	return &ColorM{
		// TODO: This is a temporary hack to calculate multiply of transposed matrices.
		// Fix mulSquare implmentation and swap the arguments.
		body: mulSquare(rhsb, lhsb, ColorMDim-1),
		translate: []float32{
			lhsb[0]*rhst[0] + lhsb[4]*rhst[1] + lhsb[8]*rhst[2] + lhsb[12]*rhst[3] + lhst[0],
			lhsb[1]*rhst[0] + lhsb[5]*rhst[1] + lhsb[9]*rhst[2] + lhsb[13]*rhst[3] + lhst[1],
			lhsb[2]*rhst[0] + lhsb[6]*rhst[1] + lhsb[10]*rhst[2] + lhsb[14]*rhst[3] + lhst[2],
			lhsb[3]*rhst[0] + lhsb[7]*rhst[1] + lhsb[11]*rhst[2] + lhsb[15]*rhst[3] + lhst[3],
		},
	}
}
func (c *ColorM) Concat(other *ColorM) *ColorM {
	if !c.isInited() {
		return other
	}
	if !other.isInited() {
		return c
	}

	lhsb := colorMIdentityBody
	lhst := colorMIdentityTranslate
	rhsb := colorMIdentityBody
	rhst := colorMIdentityTranslate
	if other.isInited() {
		if other.body != nil {
			lhsb = other.body
		}
		if other.translate != nil {
			lhst = other.translate
		}
	}
	if c.isInited() {
		if c.body != nil {
			rhsb = c.body
		}
		if c.translate != nil {
			rhst = c.translate
		}
	}

	return &ColorM{
		// TODO: This is a temporary hack to calculate multiply of transposed matrices.
		// Fix mulSquare implmentation and swap the arguments.
		body: mulSquare(rhsb, lhsb, ColorMDim-1),
		translate: []float32{
			lhsb[0]*rhst[0] + lhsb[4]*rhst[1] + lhsb[8]*rhst[2] + lhsb[12]*rhst[3] + lhst[0],
			lhsb[1]*rhst[0] + lhsb[5]*rhst[1] + lhsb[9]*rhst[2] + lhsb[13]*rhst[3] + lhst[1],
			lhsb[2]*rhst[0] + lhsb[6]*rhst[1] + lhsb[10]*rhst[2] + lhsb[14]*rhst[3] + lhst[2],
			lhsb[3]*rhst[0] + lhsb[7]*rhst[1] + lhsb[11]*rhst[2] + lhsb[15]*rhst[3] + lhst[3],
		},
	}
}
// Concat multiplies a color matrix with the other color matrix.
// This is same as muptiplying the matrix other and the matrix c in this order.