Function invert

test/hello_world_gles_proxy.c:411–429

* Inverts a 4x4 matrix. * * This function can currently handle only pure translation-rotation matrices. * Read http://www.gamedev.net/community/forums/topic.asp?topic_id=425118 * for an explanation. */

 * for an explanation.
 */
static void
invert(GLfloat *m)
{
   GLfloat t[16];
   identity(t);

   // Extract and invert the translation part 't'. The inverse of a
   // translation matrix can be calculated by negating the translation
   // coordinates.
   t[12] = -m[12]; t[13] = -m[13]; t[14] = -m[14];

   // Invert the rotation part 'r'. The inverse of a rotation matrix is
   // equal to its transpose.
   m[12] = m[13] = m[14] = 0;
   transpose(m);

   // inv(m) = inv(r) * inv(t)
   multiply(m, t);
}

/**
 * Calculate a perspective projection transformation.