setRotationMatrix function

void setRotationMatrix (Matrix4 rotationMatrix, Vector3 forwardDirection, Vector3 upDirection)

Constructs a rotation matrix in rotationMatrix.

Sets rotationMatrix to a rotation matrix built from forwardDirection and upDirection. The right direction is constructed to be orthogonal to forwardDirection and upDirection.

forwardDirection specifies the direction of the forward vector. upDirection specifies the direction of the up vector.

Use case is to build the per-model rotation matrix from vectors forwardDirection and upDirection. See sample code below for a context.

class Model {
  Vector3 _center = new Vector3.zero();        // per-model translation
  Vector3 _scale = new Vector3(1.0, 1.0, 1.0); // per-model scaling
  Matrix4 _rotation = new Matrix4.identity();  // per-model rotation
  Matrix4 _MV = new Matrix4.identity();        // per-model model-view

  void updateModelViewUniform(RenderingContext gl, UniformLocation u_MV,
    Vector3 camPosition, camFocusPosition, camUpDirection) {

    // V = View (inverse of camera)
    // T = Translation
    // R = Rotation
    // S = Scaling
    setViewMatrix(_MV, camPosition, camFocusPosition, camUpDirection); // MV = V
    _MV.translate(_center); // MV = V*T
    _MV.multiply(_rotation); // MV = V*T*R
    // _rotation is updated with setRotationMatrix(_rotation, forward, up);
    _MV.scale(_scale); // MV = V*T*R*S

    gl.uniformMatrix4fv(u_MV, false, _MV.storage);
  }
}

Implementation 

void setRotationMatrix(
    Matrix4 rotationMatrix, Vector3 forwardDirection, Vector3 upDirection) {
  setModelMatrix(rotationMatrix, forwardDirection, upDirection, 0.0, 0.0, 0.0);
}