Shifter Inside - remove top and bottom borders in GEM desktop

Copyright (c) 2023-2025 by François Galea (fgalea à free.fr)

This is a program for the Atari ST/STe which uses classical demoscene-style top and bottom border removal techniques to extend the screen size of the standard graphical interface, GEM.

It typically enables screen sizes of ×ばつ276 in medium resolution, ×ばつ276 in low resolution. No screen size improvement is available for high resolution monochrome mode.

A STE-only version also expands the horizontal size by a few pixels, achieving×ばつ276 pixels in low resolution.

Binary build

This program was developed using vasm. If the vasmm68k_mot binary is in your execution path, you should be able to build SHIN.PRG by just typing the command make.

It also should be no problem to build it using Devpac on the Atari machine.

Installation

Build and copy either of SHIN_ST.PRG or SHIN_STE.PRG into the AUTO folder of your system disk, depending the computer is a ST or a STE.

Caveats

This program does what is technically possible to use border removal on the system shell. However, such techniques usually require to work on no interrupt environments, which is not possible when running the user OS. Even though countermeasures can be used to avoid being disturbed by the system clock or keyboard interrupts, there is no known way to counteract disturbances from DMA transfers (Floppy, Blitter, ACSI devices) which basically stop the CPU during transfers.

Shifter Inside is distributed under the GNU General Public License v3 licence. See the LICENSE file or https://www.gnu.org/licenses/gpl-3.0.html for more details.