Modern computer music performances often involve a musical instrument that is primarily digital; software runs on a computer, and the physical form of the instrument is the computer. In such a practice, the performance interface is rendered on a computer screen for the performer. There has been a concern in using a laptop as a musical instrument from the audience's perspective, in that having ``a laptop performer sitting behind the screen'' makes it difficult for the audience to understand how the performer is creating music. Mirroring a computer screen on a projection screen has been one way to address the concern and reveal the performer's instrument. This paper introduces and discusses the author's computer music practice, in which a performer actively considers screen mirroring as an essential part of the performance, beyond visualization of music. In this case, screen mirroring is not complementary, but inevitable from the inception of the performance. The related works listed within explore various roles of screen mirroring in computer music performance and helps us understand empirical and logistical findings in such practices.