g3n-engine/math32/matrix3.go

// Copyright 2016 The G3N Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package math32

import "errors"

// Matrix3 is 3x3 matrix organized internally as column matrix
type Matrix3 [9]float32

// NewMatrix3 creates and returns a pointer to a new Matrix3
// initialized as the identity matrix.
func NewMatrix3() *Matrix3 {

	var m Matrix3
	m.Identity()
	return &m
}

// Set sets all the elements of the matrix row by row starting at row1, column1,
// row1, column2, row1, column3 and so forth.
// Returns the pointer to this updated Matrix.
func (m *Matrix3) Set(n11, n12, n13, n21, n22, n23, n31, n32, n33 float32) *Matrix3 {

	m[0] = n11
	m[3] = n12
	m[6] = n13
	m[1] = n21
	m[4] = n22
	m[7] = n23
	m[2] = n31
	m[5] = n32
	m[8] = n33
	return m
}

// Identity sets this matrix as the identity matrix.
// Returns the pointer to this updated matrix.
func (m *Matrix3) Identity() *Matrix3 {

	m.Set(
		1, 0, 0,
		0, 1, 0,
		0, 0, 1,
	)
	return m
}

// Copy copies src matrix into this one.
// Returns the pointer to this updated matrix.
func (m *Matrix3) Copy(src *Matrix3) *Matrix3 {

	*m = *src
	return m
}

// ApplyToVector3Array multiplies length vectors in the array starting at offset by this matrix.
// Returns pointer to the updated array.
// This matrix is unchanged.
func (m *Matrix3) ApplyToVector3Array(array []float32, offset int, length int) []float32 {

	var v1 Vector3
	j := offset
	for i := 0; i < length; i += 3 {
		v1.X = array[j]
		v1.Y = array[j+1]
		v1.Z = array[j+2]
		v1.ApplyMatrix3(m)
		array[j] = v1.X
		array[j+1] = v1.Y
		array[j+2] = v1.Z
	}
	return array
}

// MultiplyScalar multiplies each of this matrix's components by the specified scalar.
// Returns pointer to this updated matrix.
func (m *Matrix3) MultiplyScalar(s float32) *Matrix3 {

	m[0] *= s
	m[3] *= s
	m[6] *= s
	m[1] *= s
	m[4] *= s
	m[7] *= s
	m[2] *= s
	m[5] *= s
	m[8] *= s
	return m
}

// Determinant calculates and returns the determinant of this matrix.
func (m *Matrix3) Determinant() float32 {

	return m[0]*m[4]*m[8] -
		m[0]*m[5]*m[7] -
		m[1]*m[3]*m[8] +
		m[1]*m[5]*m[6] +
		m[2]*m[3]*m[7] -
		m[2]*m[4]*m[6]
}

// GetInverse sets this matrix to the inverse of the src matrix.
// Returns the pointer to this updated Matrix and an error.
// An error is returned if the src matrix cannot be inverted.
// In this case sets this matrix to the identity matrix.
func (m *Matrix3) GetInverse(src *Matrix4) (*Matrix3, error) {

	m[0] = src[10]*src[5] - src[6]*src[9]
	m[1] = -src[10]*src[1] + src[2]*src[9]
	m[2] = src[6]*src[1] - src[2]*src[5]
	m[3] = -src[10]*src[4] + src[6]*src[8]
	m[4] = src[10]*src[0] - src[2]*src[8]
	m[5] = -src[6]*src[0] + src[2]*src[4]
	m[6] = src[9]*src[4] - src[5]*src[8]
	m[7] = -src[9]*src[0] + src[1]*src[8]
	m[8] = src[5]*src[0] - src[1]*src[4]

	det := src[0]*m[0] + src[1]*m[3] + src[2]*m[6]

	// no inverse
	if det == 0 {
		m.Identity()
		return m, errors.New("Matrix3.GetInverse(): can't invert matrix, determinant is 0")
	}
	m.MultiplyScalar(1.0 / det)
	return m, nil
}

// Transpose transposes this matrix.
// Returns pointer to this updated matrix.
func (m *Matrix3) Transpose() *Matrix3 {

	var tmp float32
	tmp = m[1]
	m[1] = m[3]
	m[3] = tmp
	tmp = m[2]
	m[2] = m[6]
	m[6] = tmp
	tmp = m[5]
	m[5] = m[7]
	m[7] = tmp
	return m
}

// GetNormalMatrix set this matrix to the matrix to transform the normal vectors
// from the src matrix to transform the vertices.
// If the src matrix cannot be inverted, returns nil and an error,
// otherwise returns pointer to this updated matrix and no error.
func (m *Matrix3) GetNormalMatrix(src *Matrix4) (*Matrix3, error) {

	inv, err := m.GetInverse(src)
	if err != nil {
		return nil, err
	}
	*m = *inv.Transpose()
	return m, nil
}

// FromArray set this matrix array starting at offset.
// Returns pointer to this updated matrix.
func (m *Matrix3) FromArray(array []float32, offset int) *Matrix3 {

	copy(m[:], array[offset:offset+9])
	return m
}

// ToArray copies this matrix to array starting at offset.
// Returns pointer to the updated array.
func (m *Matrix3) ToArray(array []float32, offset int) []float32 {

	copy(array[offset:], m[:])
	return array
}

// Clone creates and returns a pointer to a copy of this matrix.
func (m *Matrix3) Clone() *Matrix3 {

	var cloned Matrix3
	cloned = *m
	return &cloned
}