Math

General purpose math functionality in Banshee is provided through the Math class. It provides a variety of familiar methods, such as Math::floor(), Math::clamp(), Math::cos() and many others. Check the API reference for a full list.

All other math functionality is provided through specific types, as listed below.

Vectors are represented by Vector2, Vector3 and Vector4 classes. All classes come with a full range of operators so manipulating vectors is easy.

Vector3 a(0.0f, 10.0f, 20.0f);

Vector3 b(-1.0f, -2.0f, -3.0f);

Vector3 c = a + b;

Vector3 d = b - a;

Vector3 scaled = a * 3.0f;

They also come with a variety of helpful methods, and some of the more useful ones are:

- Vector3::dot() - Dot product
- Vector3::cross() - Cross product
- Vector3::normalize() - Normalizes the vector
- Vector3::length() - Returns the length of the vector
- Vector3::distance() - Returns the distance between two vectors

And many more as listed on their API reference pages.

Vector3 cross = a.cross(b);

float dotProduct = a.dot(b);

float length = a.length();

Integer 2D vector type is also provided as Vector2I. It also supports a full range of operators and comes with a few helper methods. Higher level integer vector types can also be created in the form of bs::VectorNI<T>.

Vector2I intVec(0, 10);

Angles are represented using either Degree or Radian classes. They accept a raw floating point value, which they expect to be in degrees or radians, respectively. Once created the system automatically converts between the two.

Degree myAngle(90.0f);

Radian myAngle2 = myAngle;

void printAngle(Degree angle)

{

float angleValue = angle.valueDegrees();

}

// Caller doesn't need to care if the method accepts radians or degrees

printAngle(myAngle2);

Quaternions are the primary way of representing rotations in Banshee. They can be created using Euler angles, axis/angle combination, or from a rotation matrix (talked about later).

// Quaternion that rotates 30 degrees around X axis, followed by 50 degrees around Z axis (Euler angle representation)

Quaternion a(Degree(30), 0, Degree(50));

// Quaternion that rotates 40 degrees around Y axis (axis/angle representation)

Quaternion b(Vector3::UNIT_Y, Degree(40));

// Quaternion initialized from a rotation matrix

Matrix3 someMatrix = ...;

Quaternion c(someMatrix);

Once created quaternion can be used to apply rotation to a 3D vector by calling Quaternion::rotate().

Vector3 myVector(1, 0, 0);

Vector3 rotatedVector = b.rotate(myVector);

Rotations can be combined by multiplying the quaternions.

// Quaternion that applies rotation b, followed by rotation a

Quaternion combination = a * b;

Inverse of a rotation can be obtained by calling Quaternion::inverse().

// Quaternion that rotates 40 degrees around Y axis

Quaternion quat(Degree(40), Vector3::UNIT_Y);

// Quaternion that rotates 40 degrees around Y axis, in opposite direction

Quaternion invQuat = quat.inverse();

Quaternions only make sense for rotations if they are normalized. If you're doing many operations with them, due to precision issues they might become un-normalized. In such cases you can call Quaternion::normalize() to re-normalize them.

quat.normalize();

You can transform a quaternion back to a more familiar form using one of these methods:

Radian xAngle, yAngle, zAngle;

quat.toEulerAngles(xAngle, yAngle, zAngle);

Radian angle;

Vector3 axis;

quat.toAxisAngle(axis, angle);

Matrix3 rotationMat;

quat.toRotationMatrix(rotationMat);

Often you want to rotate towards a certain direction, for example making a camera look towards something. You can create such rotation by calling Quaternion::lookRotation().

Quaternion q;

// Look towards negative z axis

q.lookRotation(-Vector3::UNIT_Z);

You can interpolate between using two quaternions using Quaternion::lerp() and Quaternion::slerp(). The first method offers normal linear interpolation, and the second method offers a specialized form of interpolation possible only with quaternions, called spherical interpolation. Spherical interpolation is special because it doesn't change the magnitude of the quaternion (i.e. the interpolation happens on a surface of a sphere), while linear interpolation might require a quaternion to be re-normalized after interpolating. On the other hand linear interpolation requires less CPU cycles to execute.

Quaternion interpVal0 = Quaternion::lerp(0.5f, a, b);

interpVal0.normalize();

Quaternion interpVal1 = Quaternion::slerp(0.5f, a, b);

Sometimes you have two vectors and want to find a rotation that rotates the first vector into the position of the second. You can do that by using Quaternion::getRotationFromTo().

Vector3 from(0.0f, 1.0f, 0.0f);

Vector3 to(1.0f, 0.0f, 0.0f);

// Generates a rotation that rotates from a vector pointing towards positive Y axis, to a vector pointing towards positive X axis. Essentially creates a 90 degree rotation around the Z axis.

Quaternion quat = Quaternion::getRotationFromTo(from, to);

You can find out the rotation axes of a quaternion by calling Quaternion::xAxis(), Quaternion::yAxis() or Quaternion::zAxis(). For example you can use this to find the direction in which a quaternion is facing.

// Assuming we consider the Z axis the facing direction

Vector3 dir = quat.zAxis();

Matrices can be split into two major types: Matrix3 representing a 3x3 matrix and Matrix4 representing a 4x4 matrix. 3x3 matrices are used primarily for representing rotations, and are used similarly to quaternions. 4x4 matrices are used to represent a complete set of transformations like scale, translation and rotation, and are the most commonly used matrix type. We also provide a generic MatrixNxM<N, M> template for other matrix sizes, but they come with much simpler functionality.

**Matrix3** can be initialized using Euler angles, axis/angle combination, or from a quaternion. It can also accept a scale factor as well as rotation.

// Matrix that rotates 30 degrees around X axis, followed by 50 degrees around Z axis (Euler angle representation)

Matrix3 a(Degree(30), 0, Degree(50));

// Matrix that rotates 40 degrees around Y axis (axis/angle representation)

Matrix3 b(Vector3::UNIT_Y, Degree(40));

// Matrix initialized from a quaternion

Quaternion someQuat = ...;

Matrix3 c(someQuat);

// Matrix initialized from a quaternion, but also does scaling along with rotation

Vector3 scale(1.0f, 0.5f, 2.0f);

Matrix3 d(someQuat, scale);

To apply a matrix transformation to a 3D vector call Matrix3::transform().

Vector3 myVector(1, 0, 0);

Vector3 transformedVector = b.transform(myVector);

Matrices can be multiplied to combine their transformations.

// Creates a matrix that first applies transformation of matrix "a", followed by transformation of matrix "b"

Matrix3 combination = b * a;

Matrices can be transposed (switching rows/columns) by calling Matrix3::transpose().

Matrix3 mat(Vector3::UNIT_Y, Degree(40));

Matrix3 transpose = mat.transpose();

Matrices can be inverted by calling Matrix3::inverse(). Not all matrices have an inverse therefore this method returns a boolean which returns true if an inverse was found.

You can decompose a matrix back into rotation & scale components by calling Matrix3::decomposition(). Note that this is only able to work if the matrix contains rotation and/or uniform scale, without any other transformations. Otherwise returned values will likely not be accurate.

Quaternion rotation;

Vector3 scale;

mat.decomposition(rotation, scale);

If the matrix contains only rotation you can also use any of the following methods to extract it:

Radian xAngle, yAngle, zAngle;

mat.toEulerAngles(xAngle, yAngle, zAngle);

Radian angle;

Vector3 axis;

mat.toAxisAngle(axis, angle);

Quaternion quat;

mat.toQuaternion(quat);

**Matrix4** can be initialized using any of the following static methods:

- Matrix4::rotation() - Creates a matrix containing only rotation, from a quaternion.
- Matrix4::translation() - Creates a matrix containing only translation.
- Matrix4::scaling() - Creates a matrix containing only scale.
- Matrix4::TRS() - Creates a matrix containing translation, rotation and scale. Scale is applied first, followed by rotation and finally translation.

Quaternion rotation(Degree(90), Degree(0), Degree(0));

Matrix4 rotMat = Matrix4::rotation(rotation);

Vector3 translation(0.0f, 50.0f, 0.0f);

Matrix4 transMat = Matrix4::translation(translation);

Vector3 scale(1.0f, 1.0f, 2.0f);

Matrix4 scaleMat = Matrix4::scaling(scale);

Matrix4 combinedMat = Matrix4::TRS(translation, rotation, scale);

To apply a matrix transformation to a 4D vector you can call Matrix4::multiply().

Vector4 myVector(1, 0, 0, 1);

Vector4 transformedVector = combinedMat.multiply(myVector);

Not that a vector has its 4th component set to 1. This means the vector is treated as a point, and will be translated by the matrix. If the 4th component was 0, the vector would be treated as a direction instead, and translation would not be applied.

You can also use overriden Matrix4::multiply() to multiply a **Vector3**, in which case it is assumed to be a point (4th component is equal to 1). If you instead wish to assume a **Vector3** is a direction, use Matrix4::multiplyDirection() instead.

Vector3 myVector(1, 0, 0);

Vector3 transformedPoint = combinedMat.multiply(myVector);

// No translation applied (if matrix had any)

Vector3 transformedDirection = combinedMat.multiplyDirection(myVector);

Matrices can be multiplied to combine their transformations.

// Creates a matrix that first applies transformation of matrix "a", followed by transformation of matrix "b"

Matrix4 combination = b * a;

Matrices can be transposed (switching rows/columns) by calling Matrix4::transpose().

Matrix4 mat(Vector3::UNIT_Y, Degree(40));

Matrix4 transpose = mat.transpose();

Matrices can be inverted by calling Matrix4::inverse(). Not all matrices have an inverse therefore this method returns a boolean which returns true if an inverse was found.

You can decompose a matrix back into rotation, scale and translation components by calling Matrix4::decomposition(). Note that this is only able to work if the matrix contains rotation, translation and uniform scale, without any other transformations. Otherwise returned values will likely not be accurate.

Vector3 translation;

Quaternion rotation;

Vector3 scale;

mat.decomposition(translation, rotation, scale);

Rays are represented using an origin point, and a direction. They are often used in physics for intersection tests.

// Ray with origin at world origin, looking up

Ray ray(Vector3(0, 0, 0), Vector3(0, 1, 0));

You can use Ray::getPoint() to get a point some distance from ray origin, along the direction.

Vector3 point = ray.getPoint(10.0f);

Rays can be transformed by matrices by calling Ray::transform().

Matrix4 mat = ...;

ray.transform(mat);

They also provide a series of *intersects* methods that allow them to test for intersection against axis aligned boxes, spheres, planes and triangles:

- Ray::intersects(const AABox&) - Axis aligned box intersection
- Ray::intersects(const Sphere&) - Sphere intersection
- Ray::intersects(const Plane&) - Plane intersection
- Ray::intersects(const Vector3&, const Vector3&, const Vector3&) - Triangle intersection

Rect2 and Rect2I structures can be used for storing rectangles using floating point or integer values, respectively. Check their API reference for the methods they support, but in most scenarios you will be using them for storage and method parameters.

Banshee supports a variety of other 3D shapes:

We'll let you deduce how they are used from their API reference, as it should be fairly self explanatory. All of the shapes provide a way be initialized, to be transformed by a world matrix as well a set of intersection tests against rays and other shapes.

// Axis aligned box created from minimum and maximum corners

Vector3 min(-1.0f, -1.0f, -1.0f);

Vector3 max(1.0f, 1.0f, 1.0f);

AABox box(min, max);

// Sphere created from center and radius

Vector3 center(0.0f, 10.0f, 0.0f);

float radius = 20.0f;

Sphere sphere(center, radius);

// Plane created from normal, and distance from origin along the normal

Vector3 normal(0.0f, 1.0f, 0.0f);

float dist = 10.0f;

Plane plane(normal, dist);