Vertical game on a horizontal monitor aspect ratio calculation

[jimj]

Vertical game on a horizontal monitor aspect ratio calculation

I'm surprised I haven't been able to find more information about this on the message boards.  I know that there has to be more info on this already out there, so please post any links I missed.  The closest thing I could find was this post http://forum.arcadecontrols.com/index.php/topic,13625.msg106993.html#msg106993  Basically he divides the vertical resolution by the horizontal resolution to get a scaling factor.  My feeble mind can't understand how this would work, so I've come up with my own scaling factor.

At first this calculation sounded complicated to figure out, but once I've written out the algebra it looks pretty simple.  This, of course, can mean only one thing.  I have messed this up royally and oversimplified the problem.   So if anyone could double check my math below and let me know where I went wrong I'd appreciate it.

I've got the standard problem of making vertical games look good on a horizontal monitor.  My specific problem is trying to get a vertical game which has a 3:4 aspect ratio maintain the correct aspect ratio when displayed on a 4:3 horizontal monitor.

My first assumption is that since a horizontal monitor has a 4:3 aspect ratio even a square resolution like 240x240 will actually have a 4:3 aspect ratio when displayed if it fills up the whole screen.  If this simple assumption is wrong, then my calculation won't work.  I'm using an AVGA card with a Betson Multisync monitor, so most of the AVGA resolutions come close to filling up my whole screen.

All of these conditions must also be true for my calculation to work:
-Monitor is mounted horizontally and has a 4:3 aspect ratio (i.e. a standard monitor)
-The aspect ratio of the vertical game you want to display is 3:4 (i.e. a standard vertical game)
-hwstrech is off
-no artwork
-Vertical resolution exactly fills up the entire vertical portion of the screen.  For example the monitor will display exactly 240 lines, and have them fill the entire vertical portion of the screen for a 224x240 vertical game.
-You don't change the vertical resolution of the games (i.e. for a 224x240 game you can change the 224 number, but you'll aways use 240 for the vertical resolution).

It's also important to keep in mind that as HC points out here http://forum.arcadecontrols.com/index.php/topic,21170.msg171994.html#msg171994 "there are only about 4 valid aspect ratios for arcade games, which btw have absolutely nothing to do with the resolution."  The last paragraph of this post has a good analogy about why resolution is not equal to aspect ratio http://forum.arcadecontrols.com/index.php/topic,21170.msg171716.html#msg171716

Here are the variables I used in my calculation:
O = Original horizontal resolution of the vertical game
S = Horizontal resolution that makes the game appear square on the monitor
F = Final horizontal resolution that will give your vertical game a 3:4 aspect ratio

I basically attacked this problem in two parts.  First, since my horizontal monitor has a 4:3 aspect ratio, this means that the game will appear a third wider than a true square if it fills up the whole screen.  To solve this you need to make the game take up a third less horizontal space on the screen to get a 1 to 1 aspect ratio (i.e. a square).   To say this with algebra 4/3

[desmatic]

Vertical game on a horizontal monitor aspect ratio calculation

I'm surprised I haven't been able to find more information about this on the message boards.  I know that there has to be more info on this already out there, so please post any links I missed.  The closest thing I could find was this post http://forum.arcadecontrols.com/index.php/topic,13625.msg106993.html#msg106993  Basically he divides the vertical resolution by the horizontal resolution to get a scaling factor.  My feeble mind can't understand how this would work, so I've come up with my own scaling factor.

At first this calculation sounded complicated to figure out, but once I've written out the algebra it looks pretty simple.  This, of course, can mean only one thing.  I have messed this up royally and oversimplified the problem.   So if anyone could double check my math below and let me know where I went wrong I'd appreciate it.

I've got the standard problem of making vertical games look good on a horizontal monitor.  My specific problem is trying to get a vertical game which has a 3:4 aspect ratio maintain the correct aspect ratio when displayed on a 4:3 horizontal monitor.

My first assumption is that since a horizontal monitor has a 4:3 aspect ratio even a square resolution like 240x240 will actually have a 4:3 aspect ratio when displayed if it fills up the whole screen.  If this simple assumption is wrong, then my calculation won't work.  I'm using an AVGA card with a Betson Multisync monitor, so most of the AVGA resolutions come close to filling up my whole screen.

All of these conditions must also be true for my calculation to work:
-Monitor is mounted horizontally and has a 4:3 aspect ratio (i.e. a standard monitor)
-The aspect ratio of the vertical game you want to display is 3:4 (i.e. a standard vertical game)
-hwstrech is off
-no artwork
-Vertical resolution exactly fills up the entire vertical portion of the screen.  For example the monitor will display exactly 240 lines, and have them fill the entire vertical portion of the screen for a 224x240 vertical game.
-You don't change the vertical resolution of the games (i.e. for a 224x240 game you can change the 224 number, but you'll aways use 240 for the vertical resolution).

It's also important to keep in mind that as HC points out here http://forum.arcadecontrols.com/index.php/topic,21170.msg171994.html#msg171994 "there are only about 4 valid aspect ratios for arcade games, which btw have absolutely nothing to do with the resolution."  The last paragraph of this post has a good analogy about why resolution is not equal to aspect ratio http://forum.arcadecontrols.com/index.php/topic,21170.msg171716.html#msg171716

Here are the variables I used in my calculation:
O = Original horizontal resolution of the vertical game
S = Horizontal resolution that makes the game appear square on the monitor
F = Final horizontal resolution that will give your vertical game a 3:4 aspect ratio

I basically attacked this problem in two parts.  First, since my horizontal monitor has a 4:3 aspect ratio, this means that the game will appear a third wider than a true square if it fills up the whole screen.  To solve this you need to make the game take up a third less horizontal space on the screen to get a 1 to 1 aspect ratio (i.e. a square).   To say this with algebra 4/3

[jimj]

modeline monitor howto at http://easymamecab.mameworld.net

the page your looking for is http://easymamecab.mameworld.net/html/monitor8.htm

Looks like I don't know how to make a square, doh. At least I was right in guessing that my solution wasn't correct.

Wow, thanks for the great link!  That has everything I ever wanted to know about arcade monitors.  Should add it to the monitor FAQ here.

The solution there is very easy to follow, I now see that the magic ratio is 16/9.  Calculating Galaga's horizontal resolution now yields 398 which means the best AVGA resolution is still 384x288, not 352x288.  Any ideas why Andy and Minwah would choose 352x288 instead?

[desmatic]

Any ideas why Andy and Minwah would choose 352x288 instead?

No idea why.  Advancemame or SDL (i never bothered to figure out which) uses .56 instead of .5625,  but 352?  It's not even close.

[AndyWarne]

I don't dispute the maths, but I just think 352 X 288 looks better for Galaga. Running vertical games on a horizontal monitor is always something of a compromise, so it just becomes more of a subjective issue.

Andy