VkSRTDataNV

An acceleration structure SRT transform is defined by the structure:

typedef struct VkSRTDataNV {
    float sx;
    float a;
    float b;
    float pvx;
    float sy;
    float c;
    float pvy;
    float sz;
    float pvz;
    float qx;
    float qy;
    float qz;
    float qw;
    float tx;
    float ty;
    float tz;
} VkSRTDataNV;

sx is the x component of the scale of the transform
a is one component of the shear for the transform
b is one component of the shear for the transform
pvx is the x component of the pivot point of the transform
sy is the y component of the scale of the transform
c is one component of the shear for the transform
pvy is the y component of the pivot point of the transform
sz is the z component of the scale of the transform
pvz is the z component of the pivot point of the transform
qx is the x component of the rotation quaternion
qy is the y component of the rotation quaternion
qz is the z component of the rotation quaternion
qw is the w component of the rotation quaternion
tx is the x component of the post-rotation translation
ty is the y component of the post-rotation translation
tz is the z component of the post-rotation translation

This transform decomposition consists of three elements. The first is a matrix S, consisting of a scale, shear, and translation, usually used to define the pivot point of the following rotation. This matrix is constructed from the parameters above by:

S = \left( \begin{matrix} sx & a & b & pvx \\\ 0 & sy & c & pvy \\\ 0 & 0 & sz & pvz \end{matrix} \right)

The rotation quaternion is defined as:

R = [ qx, qy, qz, qw ]

This is a rotation around a conceptual normalized axis [ ax, ay, az ] of amount theta such that:

[ qx, qy, qz ] = sin(theta/2) × [ ax, ay, az ]

and

qw = cos(theta/2)

Finally, the transform has a translation T constructed from the parameters above by:

T = \left( \begin{matrix} 1 & 0 & 0 & tx \\\ 0 & 1 & 0 & ty \\\ 0 & 0 & 1 & tz \end{matrix} \right)

The effective derived transform is then given by

T × R × S