Psst! Math

Small C++17 template library for vector and matrix computations.

Library provides easy syntax for declaring, assigning vectors and matrices and making calculations. The vector and matrix classes are designed to have a memory layout as C++ arrays of respective elements, and can be passed to rendering libraries where pointers to floats (for example) are required. The library uses lazy expression templates for calcutations.

Vectors and Matrices

Usage Synopsis

Declaration and assignment

// Vector
#include <psst/math/vector.hpp>

using vector3d = psst::math::vector<float, 3>;

vector3d p1{1, 2, 1.5}, p2{2, 3, 5.4};

// Matrix
#include <psst/math/matrix.hpp>

using matrix3x3 = psst::math::matrix<float, 3, 3>;

matrix3x3 m1 {
  { 1,  2,  3 },
  { 4,  5,  6 },
  { 7,  8,  9 }
};

using affine_matrix = psst::math::matrix<float, 4, 4>;

affine_matrix
rotate_x( float a )
{
  using std::cos;
  using std::sin;
  return
  {
    {  1  ,     0   ,      0  ,   0  },
    {  0  , cos(a)  , -sin(a) ,   0  },
    {  0  , sin(a)  ,  cos(a) ,   0  },
    {  0  ,     0   ,      0  ,   1  }
  };
}

Element access

vector class provides access to all elements by indexes (subscript operator) and template function at<N>(). First four elements of vector are accessible by named functions x(), y(), z() and w() respectively. Those functions are defined only where the size of vector allows it, e.g. for a three-element vector there will be no w() function. Vectors elements can be iterated with a C++11 range loop or using iterators.

matrix class provides subscript operator and template function at<N>() to access rows that are represented by vectors. Iterators to rows are provided by row_begin()/row_end() function pairs. begin()/end() pairs will provide iterators over all matrix elements, in the order a C++ two-dimensional array would be layed out.

using vector4 = psst::math::vector<float, 4>;
vector4 v1{1, 2, 3, 4};

auto x = v1[0];
x = v1.at<0>();
x = v1.x();
auto y = v1[1];
y = v1.y();
auto z = v1[2];
z = v1.z();
auto w = v1[3];
w = v1.w();

v1.x() = x;
v1.at<0>() = x;
v1[0] = x;
v1.y() = y;
v1.z() = z;
v1.w() = w;

matrix3x3 m1 {
  { 1,  2,  3 },
  { 4,  5,  6 },
  { 7,  8,  9 }
};
m1[0][0] = 5;
auto a = m1[2].z();
m1[1].y() = 8;

Operations

// Vector
vector3d v3 = v1 + v2;  // vector sum
v3 = v1 - v2;           // vector difference
v3 = -v1;               // negate vector
v3 *= 3;                // multiply by scalar
v3 = v1 * 5;
v3 /= 5;                // divide by scalar
v3 = v2 / 10;

v3 = normalize(v1);     // normalize vector
auto s = v3.magnitude_square(); // vector magnitude squared
s = v3.magnitude()      // vector magnitude

auto p = v1 | v2; // dot product
v3 = v1 * v2;     // cross product. Defined for 3D vectors only

v3 = projection( v1, v2 ); // projection of vector v2 onto vector v1
v3 = perpendicular( v1, v2 ); // vector that is perpendicular to v1, such as v3 + projection( v1 , v2 ) == v2
std::pair< vector3d, vector3d > pair = project( v1, v2 ); // a pair of projection of v2 onto v1 and a perpendicular to v1

auto s = distance_square(v1, v2); // returns squared magnitude of vectors difference. Semantic sugar when vectors are treated as coordinates
s = distance( v1, v2 );           // magnitude of vectors difference

// Matrix
matrix3x3
m1 {
  { 1,  2,  3 },
  { 4,  5,  6 },
  { 7,  8,  9 }
},
m2 {
  { 9,  8,  7 },
  { 6,  5,  4 },
  { 3,  2,  1 }
};

auto m3 = m1 + m2;              // matrix sum
m3 = m1 - m2;                   // matrix difference
m3 = m1 * 5;                    // matrix scalar multiplication
m3 *= 4;
m3 = m2 / 8;                    // matrix scalar division
m3 /= 3;
auto i = matrix3x3::identity(); // identity matrix

// Rectangular matrices
using matrix4x3 = psst::math::matrix<float, 4, 3>;
using matrix3x4 = psst::math::matrix<float, 3, 4>;

matrix4x3 r1 {
  { 1,  2,  3 },
  { 1,  2,  3 },
  { 1,  2,  3 },
  { 1,  2,  3 }
};
matrix3x4 r2 {
  { 1, 2, 3, 4 },
  { 1, 2, 3, 4 },
  { 1, 2, 3, 4 }
};

matrix3x4 t = transpose(r1);          // matrix transposition
matrix3x3 m4 = r1 * r2;               // matrix multiplication
vector3d v4 = m1 * as_col_matrix(v1); // matrix by vector multiplication
vector3d v5 = as_row_matrix(v1) * m1; // vector by matrix multiplication

Output

#include <iostream>
#include <psst/math/vector_io.hpp>
#include <psst/math/matrix_io.hpp>

namespace io = psst::math::io;

std::cout << v1 << "\n";
// output {1,2,1.5}
std::cout << m1 << "\n";
// output {{1,2,3},{4,5,6},{7,8,9}}
std::cout << io::pretty << m1 << io::ugly << "\n";
// output
// {
//      { 1, 2, 3 },
//      { 4, 5, 6 },
//      { 7, 8, 9 }
// }

Memory buffers as vectors

A memory buffer can be accessed as a container of vectors with certain properties (size, components). A constant buffer can be used to read data in a structured manner, a non-costant buffer can be used to modify data in the buffer via vector_view and memory_vector_view utility classes. A vector_view is for reading a single element, memory_vector_view is for using a buffer as a 'container' of vectors.

#include <psst/math/vector_view.hpp>

using namespace psst::math;

// Size of the vector is 16 bytes
using vec4f = vector<float, 4>;

char const* const_buffer = "..."; // Get this buffer somewhere
std::size_t buffer_size = 256; // this is 16 vectors

auto const_mem_view = make_memory_view<vec4f>(const_buffer, buffer_size);

for (auto mv : const_mem_view) {
  // do something with the vectors, no modification is available
}

char const* mutable_buffer = "..."; // Get this buffer somewhere

auto mem_view = make_memory_view<vec4f>(mutable_buffer, buffer_size);

for (auto mv : mem_view) {
  // do something with the vectors, modification is available
  mv *= 2;
}

Quaternions

The libbrary provides quaternions and operations with them, such as sum, substraction, multiplication and division by scalar, quaternion multiplication, magnitude, normalize, conjugate and inverse functions. Components of a quaternion are accessible via w(), x(), y() and z() accessors, where w() is the real part and x(), y() and z() are coefficients for i, j and k respectively. Also, the scalar part is accessible via scalar_part() member function, and the vector part is accessible via vector_part().

#include <psst/math/quaternion.hpp>

using quat = psst::math::quaternion<double>;

quat q1{1, 2, 3, 4}, q2{5, 6, 7, 8};
// quaternion sum and difference
auto sum = q1 + q2;
auto diff = q1 - q2;
// multiplication and division by scalar
auto mul = q1 * 2;
auto div = q2 / 3;
// quaternion multiplication
auto q3 = q1 * q2;
// misc function
auto mag = magnitude(q1);
auto c = conjugate(q2);
auto u = normalize(q1);
auto i = inverse(q2);

Example of Using Quaternions for Rotation

#include <psst/math/quaternion.hpp>

using quat = psst::math::quaternion<double>;
using vec3 = psst::math::std::vector<double, 3>;

vec3
rotate(vec3 v, vec3 axis, double angle)
{
    using std::cos;
    using std::sin;
    auto unit = normalize(quat{ 0, axis.x(), axis.y(), axis.z() });
    auto rot =  quat{cos(angle / 2), 0, 0, 0} + unit * sin(angle / 2);
    return (rot * quat{0, v.x(), v.y(), v.z()} * inverse(rot)).vector_part();
}

Polar, Spherical and Cylindrical Coordinates

The library provides polar, spherical and cylindrical coordinates and conversion between them and XYZ coordinates.

Components of polar coordinates:

1. 0 r() or rho(), the radius component.

2. 1 phi() or azimuth(), the azimuth component, the value is in radians between zero and 2π, the value is normalized automatically.

Componetns of spherical coordinates:

1. 0 r() or rho(), the radius component.

2. 1 phi() or inclination(), the angle between the projection on the plane and vector. The range of value is [-π/2, π/2], the value is clamped automatically.

3. 2 theta() or azimuth(), the azimuth component, the value is in radians between zero and 2π, the value is normalized automatically.

Components of cylindrical coordinates:

1. 0 r() or rho(), the radius component.

2. 1 phi() or azimuth(), the azimuth component, the value is in radians between zero and 2π, the value is normalized automatically.

3. 2 z() or elevation(), the height above zero.

Conversion is defined for:

• XYZ <-> polar
• XYZ <-> spherical
• XYZ <-> cylindrical
• polar <-> spherical
• polar <-> cylindrical
• spherical <-> cylindrical

#include <psst/math/polar_coord.hpp>
#include <psst/math/spherical_coord.hpp>
#include <psst/math/cylindrical_coord.hpp>

using polar_c       = psst::math::polar_coord<double>;
using spherical_c   = psst::math::spherical_coord<double>
using cylindrical_c = psst::math::cylindrical_coord<double>;
using vec3          = psst::math::vector<double, 3>;

using psst::math::operator "" _deg;

polar_c p{10, 180_deg};
spherical_c s = convert<spherical_c>(p);
s.inclination() = 45_deg;
cylindrical_c c = convert<cylindrical_c>(s);
vec3 v = convert<vec3>(c);

Colors

Based on vector class and expressions, the library provides classes for color calculateions in RGB, HSL ans HSV color spaces. For color classes the following operations are defined:

• sum and difference
• multiplication and division by scalar
• lerp and slerp

Components of rgba color:

1. 0 r() or red()

2. 1 g() or green()

3. 2 b() or blue()

4. 3 a() or alpha()

Components of hsla color:

1. 0 h() or hue()

2. 1 s() or saturation()

3. 2 l() or lightness()

4. 3 a() or alpha()

Components of hsva color:

1. 0 h() or hue()

2. 1 s() or saturation()

3. 2 v() or value()

4. 3 a() or alpha()

Conversions are defined for:

• RGB <-> HSL
• RGB <-> HSV

#include <psst/math/colors.hpp>

using rgba = psst::math::colors::rgba<float>;
using hsla = psst::math::colors::hsla<float>;
using hsva = psst::math::colors::hsva<float>;

using psst::math::operator "" _rgba;

rgba col1 = convert<rgba>( 0xff0000ff_rgba ); // red
hsla hl1  = convert<hsla>(col1);
hsva hv1  = convert<hsva>(col1);