Tex. Code Crim. Proc. art. 24.13

All persons who have been or may be convicted in this state, and who are confined in an institution operated by the Texas Department of Criminal Justice or any jail in this state, shall be permitted to testify in person in any court for the state and the defendant when the presiding judge finds, after hearing, that the ends of justice require their attendance, and directs that an attachment issue to accomplish the purpose, notwithstanding any other provision of this code. Nothing in this article shall be construed as limiting the power of the courts of this state to issue bench warrants.