Doom 3 Screen Resolution Fix

[Dunstan Jomphe]

Aspectratio is a term which refers to the ratio between the width and height of a logical frame buffer, called the logical aspect ratio, or a physical video display device, called the physical aspect ratio.

Most of the Doom in-game graphics appear to have been specifically designed for the 320x200 resolution as stretched to a 4:3 physical aspect ratio; for example, the appearance of the title screen better matches the Doom box art when using the rectangular pixels unique to this hardware video mode. Similarly, the shape of the status bar face better matches the dimensions of a real human face.

Because screenshots only capture the logical frame buffer contents and are not affected by the VGA rasterization process, they will similarly appear flattened (in the 8:5 logical ratio) when viewed inside a square-pixel screen mode.

Various problems arise for source ports in the area of supporting Doom's natural 4:3 aspect ratio. Support for Mode 13h, and especially for undocumented VGA tweaks like those used by Doom, has dropped to near non-existence in modern video hardware and operating systems. For example, flat panel high-definition monitors are now the default, and virtually all have a physical aspect ratio of 16:9 or 16:10. Even if Mode 13h were successfully displayed in fullscreen on these monitors, it would appear incorrect, barring possible low-level pillarboxing implemented in the monitor's firmware or video card drivers - most if not all models lack this, and use the entire display surface regardless.

Some source ports include aspect ratio correction. This performs stretching of the logical frame buffers's contents when running in a 4:3 screen mode, so that the graphics appear as they appeared in Vanilla Doom. This is generally accomplished in one of two ways:

Widescreen modes add an extra level of complication to the aspect ratio issue. Most modern monitors have a physical 16:9 or 16:10 aspect ratio, rather than the "traditional" 4:3 aspect ratio. In this scenario, the aspect ratio correction should still be performed. The extra horizontal space is properly used by either increasing the horizontal field of view or by simply filling it with a black border, which is referred to as "pillarboxing."

Some source ports handle 4:3 screen modes in a different fashion. An example is Doom 95, which renders the screen with a different type of aspect ratio correction when running in 640x480 mode. Instead of stretching the pixels, it expands the viewable area. The result is that the player can see more when running in 640x480 mode than in 320x200 or 640x400 mode.

Doom Legacy and ReMooD are both locked in a 4:3 aspect ratio, however it is only effective if the full size image matches that aspect ratio. That is, regardless of which resolution the game runs at, as long as the screen fits a 4:3 display it will appear correct. Using a mode such as 320x240 or 640x480 on a 4:3 display will result in over stretching but will appear correct on a 1:1 display. Using 320x200 or 640x400 on a 4:3 display will appear correct but will be shrunken on a 1:1 display. This results in a field of view that is constant, however certain resolutions whether in a window or full screen will not appear correct.

The Doom engine's original resolution of 320x200 corresponds to a logical 16:10 aspect ratio; however, it was not intended for widescreen displays, but to be stretched vertically into the equivalent of 320x240. For this reason, a "lazy" way to support widescreen resolutions is to simply withhold aspect ratio correction, resulting in a squashed image. Proper widescreen support requires instead rendering additional areas on the side (effectively increasing the player's field of vision), but runs into the problem that many graphics, such as the title screen or the status bar, are only 320 texels wide. This is typically addressed by addition of borders and is known as pillarboxing. In recent years, however, source ports as well as official re-releases of the Doom games now feature additional widescreen graphics for things like the status bar or title screen.

Chocolate Doom can be run in full screen or within a window. Internally and in common with vanilla, Chocolate Doom renders to a 320x200 buffer. This buffer is then scaled up to your display size or chosen window size using hardware acceleration.

In order to fit the 4:3 ratio picture within your display, it may be necessary to windowbox or letterbox with a black border. Most modern displays are 16:9 or 16:10 ratio, meaning Chocolate Doom's image will be windowboxed.

Chocolate Doom's video code supports an assortment of different window sizes (see below), and accurately preserves the original 4:3 aspect ratio of Doom on square pixel modes. Chocolate Doom's Setup program can be used to change the resolution.

The maximum supported screen resolution is 1600x1200. Only a fixed set of modes are supported, however; as a result, the screen may appear windowboxed with a black border if there is not an exact scale factor for the chosen screen mode.

From what I understand - please tell me if I got it wrong - the game was intentionally developed in a "wrong" aspect ratio in order to appear "right" back then. DOS uses resolutions which are exactly 4:3, for instance 320x200 (instead of 320x240, which would be 4:3). However, CRT monitors back then were 4:3. Therefore, I assume, the game was intentionally developed in a "wrong" aspect ratio. Wrong in the way, that things would look wrong if CRTs had set pixels with an aspect ratio of 1:1 each as they appear on our LCD based screen nowadays. Developers assumed that players would want to fill in their entire screens when playing the game, resulting in stretching an image to 4:3 that was originally not 4:3 (because 320x200 is not equivalent to 4:3).

Hope it's clear what I mean. You can see it in Doom builder that textures which are 128x128 don't look as squarish as they should, or that projectiles such as the Imp's red fireball looks rather oval than round.

I suppose it should be no problem to force the image to look right. But I guess the problem with this would be that it would result in a scaled imagine if I'm correct, because the aspect ratio of the pixels in our modern non-CRT screens can't be changed, they will remain 1:1 regardless.

Maybe this is all old news to you and has been discussed, but I haven't found much so I was wondering whether this has never been discussed or fixed by one of the source ports. Is there a fix I am not aware of?

I don't think you searched in quite the right place, we already have detailed articles about the aspect ratio. No, it's not wrong. That's just how DOS, VGA modes and monitors worked back then; pixels weren't expected to be square, an attribute also shared by TVs. It's not until digital signals and LCD monitors were introduced that this concept of display aspect ratio meaning view size became the norm. All currently developed source ports already correctly account for this behaviour.

You can't find the option because it's not optional in most ports; aspect ratio correction via pixel stretching is always enabled, with no way to turn it off. What exactly do you mean by "looks wrong"? Most of Doom's graphics were scanned from real-world models and artwork, so there's no room for subjective opinions; the aspect ratio is either correct to the original art or it isn't. Can you post a screenshot?

Look at the screenshot. Doors or the texture shown in the screenshot are 128x128 units in Doom, which is 1:1. However, they do not look like they are 1:1. 1:1 would be a perfect square and the circle would be round, not oval. That's all because the game was coded in a resolution common for DOS resolution with an aspect ratio 16:10 with the expectation of the end user stretching the image to 4:3 on their monitor.

Oh, is that all? Yes, obviously not all of the graphics properly take the aspect ratio into account; this is actually a really common oversight in games from this era. That marble face texture is actually kind of an odd example, because although the circle was clearly just drawn with the circle tool in a paint program that didn't have aspect ratio correction, the goat skull does have correct proportions when viewed with the game's stretched aspect ratio, and would look wrong if displayed with square pixels.

(If you want to see round circles in Doom, look no further than the rocket explosion, or the chaingun's barrel clamps, or the rocket launcher's muzzle. These are all ovals if incorrectly drawn with square pixels, but perfectly circular with the stretched pixels of VGA 320x200.)

When aspect ratio correction is not applied, the graphics appear squashed, like someone's compressing them vertically, or stretching them horizontally. What you're describing is actually the opposite, where what you say is supposed to be a square is instead a bit taller than that.

If you want to see what the game looks like without aspect ratio correction, go to dsda-doom and set it to a 16:10 resolution, for example 960x600 or 1920x1200, then select the 4:3 aspect ratio (both the resolution and aspect ratio options are on the first page of general options). Your texture will appear square, but this is actually without aspect ratio correction.

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