Many classic arcade games like Pac Man (Namco 1980), Assault (Namco 1988), Mercs (Capcom 1990), etc, use a monitor oriented vertically. I assume that they used the same physical hardware, with the scan lines following the long side of the monitor.

With the monitor rotated, and scan lines going in a different direction, what consequences were there for the game programmer?

Small extra question, were all vertical games' monitors rotated 90° in the same direction, or were some rotated clockwise and others anticlockwise?

  • 3
    Your question would benefit from copy editing (improved grammar) and clarification about what the problem actually is Apr 2, 2021 at 10:49
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    90° is easy; it's just a really simple co-ordinate transform. (Plot a graph, stick on a point – say, (1, 1), or (2, 5) – and rotate it 90° around (0, 0).) I think this question would be more interesting (and on-topic) if it asked about methods used for general rotations in arcade games.
    – wizzwizz4
    Apr 2, 2021 at 12:27
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    Then again… I am actually curious now whether games used separate hardware switches (or logic gates) to remap the lines in some way. I would do it in software, but when every cycle counrs…
    – wizzwizz4
    Apr 2, 2021 at 12:31
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    Didn't we already have this?
    – Raffzahn
    Apr 2, 2021 at 13:06
  • @wizzwizz4 I guess it may relate to Line Blanking and pseudo-3d thus not limited to simple transformation.
    – Schezuk
    Apr 4, 2021 at 5:38

1 Answer 1


Globally, a "vertical" game is a normal "horizontal" game.

Consider the game as if the "up" side of the monitor is the "right" side of the monitor in its normal position (rotated 90° anticlockwise).

You program it really programmed normally, BUT:

  • All fonts, sprites, etc. are rotated 90° clockwise, so they will be correct with monitor's final position.
  • Your scrolling is from right to left, so it will be from up to bottom at the end (like in "1942", for example).
  • You still wait normally for HBL/VBL when needed, and framerate isn't modified at all.
  • Scanlines are indeed vertical if monitor is simply rotated. If the monitor was built "vertical", then scanlines are horizontal and you simply have a strange video mode.
  • The tricky part is joystick: when you read (resp.) "up/left/down/right" on the joystick, you must interpret it as (resp.) "right/up/left/down", so movements are consistent with the final monitor position. Please note that you can also rewire direction inputs on the PCB internally, so you can still use the standard JAMMA connector and pinout, but internally, you decide to wire the JAMMA "up" as a "right". It may allows to use the exact same hardware (and even some code ROMs) for both horizontal and vertical games with only some jumpers onboard to set the mode.

So things aren't so different for the programmer, but for direction inputs if problem isn't solved directly through hardware. It was a bit more different for the graphic designer, first because of the rotation, and second because the aspect ratio MAY have an influence on design with some video modes, because not only are the pixels still not square, but they are also oriented in the opposite direction as usual.

  • confirmed with scramble disassembly. X and Y are swapped all right. Oh and it's even more complex with cocktail mode when the screens are inverted to face the player on the cocktail table. Mar 26, 2022 at 17:06
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    @Jean-FrançoisFabre Cocktail is another thing. For example, if your vertical resolution is a power of two (ex: 256 pixels), you can set up a hardware circuit that will swap the address lines from/to video chip, so that when you emit the line 0, it emits the line 255, line 1 becomes line 254, and so on. So, image is flipped vertically without needing to have all tiles in two directions, or to do a software trick that CAN made one mode slower than the other.
    – Wisblade
    Mar 26, 2022 at 17:12
  • this is probably what happens, you're right. Else it would take twice as much the memory just for a possible cocktail mode Mar 26, 2022 at 17:19
  • Cocktail operation is interesting; from what I can tell, many games had hardware to flip some aspects of the display, but not necessarily everything. As a consequence, if glitches result in the screen being inverted in hardware without software knowing about it, or vice versa, that may result in e.g. objects whose shapes are upside down, being shown on an inverted background, but moving the same way as they would if the screen were upright.
    – supercat
    Mar 26, 2022 at 17:36
  • @supercat Another thing is that cocktail mode is often something that isn't properly emulated with a LOT of games, so it's clearly not a matter of a pure software operation (otherwise, it would work already since the ROMs, and then the software, is already dumped). It's clearly a missing hardware device that has an effect only when the 2nd player is active in Cocktail mode... When setting the dip switches to standard mode, 2nd player can play normally. The hardware flip could also be done only on tiles/graphic ROM, not on the video circuit itself.
    – Wisblade
    Mar 27, 2022 at 0:03

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