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First post, by VileR

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A bunch of really old Atarisoft games had the option to "roll" the whole screen left and right on CGA (Gremlins and Moon Patrol at least, maybe others).

Another CGA game called BRICKS (freeware) has a left, right, up AND down adjustment for the entire display.

This does nothing in dosbox (machine=cga of course). Is this an unhandled CGA feature?
Maybe someone with a debugger and some hardware knowledge can figure out what it's trying to do?

Reply 2 of 5, by ripsaw8080

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It is also seen in Trixter's CGA compatibility test program here. The specific test is under "M6845 Compatibility", "Display Positioning" on the menu.

The horizontal and vertical sync position registers (index 7 and 8 of the MC6845 CRTC) are the ones involved. See write_crtc_data_other() in vga_other.cpp for reference. Do games lose any important functionality by not having support for the positioning?

Reply 3 of 5, by VileR

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ripsaw8080 wrote:

Do games lose any important functionality by not having support for the positioning?

No. I was curious whether the same functionality might have other (less-obvious uses) though. Thanks for the info.

(haha, Striker = total cult classic.... at least for me, since it was the only "chopper game" I had on the PC while my friends were all "Choplifter"-this and "Captain Goodnight"-that with their Apple II's)