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Last modified: Fri Feb 20 16:44:45 EST 2009

Test method for source ports

Test procedure

  1. Install the port.
  2. Configure it as best can.
  3. Play E1M1 (Hangar) and look for reasons to trash it.
  4. If no reasons are found, play DOOM2 Level 3 (The Gantlet) and look for reasons to trash it.
  5. If I still have no reason to trash it, come back when time permits and play other levels until a discrepancy is found.

Following are four simple compatibility tests that can all be conducted in the vicinity of the starting point of E1M1.

Test #1:  Aspect Ratio

Examine the rectangular texture on the far wall dead ahead.  In Vanilla DOOM, the rectangle is slightly taller than it is wide.  In source ports with broken aspect ratio correction, the same texture appears to be slightly wider than it is tall.

Right: 

Wrong: 

Test #2:  That Sinking Feeling

Also from the starting position of E1M1, examine the barrel to your right.  Note that it has three horizontal ridges.  In Vanilla DOOM, the bottom ridge is as far from the floor as the top ridge is from the top of the barrel.  In some source ports, this barrel sinks into the floor so that the bottom ridge is basically on the floor.

Right:     Wrong: 

Ironically, this problem results from correct rendering of incorrect WAD data.  When an object has a Z coordinate (altitude) that is set too low, such that it should penetrate the floor, the Vanilla DOOM renderer draws the entire object anyway.  When the same data are used by a rendering engine that does the "right" thing, the affected object actually does sink into the floor.  Some ports rectify the problem by increasing the Z of affected objects, but the result doesn't look the same as Vanilla DOOM.

Test #3:  The Steep Stairs of Doom

This is the stairway that is to the left at the beginning of E1M1.  On Ultraviolence, there are goons hiding behind each of the columns (you can see the tops of their heads in this screenshot).  If you run up the stairs and hide in the back, do they follow you up the stairs?  In Vanilla DOOM, they can't.  In some source ports, they do.  Sometimes there is a compatibility switch affecting exactly this behavior.

Test #4:  The Long Shot

This is the view through the window that is to the right at the beginning of E1M1.  In the distance, in the part of the building on the other side of the courtyard, two goons are walking back and forth.  Can you take them out?  In Vanilla DOOM, it's pretty easy.  In some source ports, it's difficult or impossible.

Evaluation criteria

Requirements

  1. DOOM levels from DOOM.WAD and DOOM2.WAD must play almost exactly as they did in Vanilla DOOM, the only permissible changes being to correct serious bugs that existed in Vanilla DOOM.  I don't want a new game that is better than DOOM—I want DOOM.  Modes of failure:  monsters do things that they couldn't do in Vanilla DOOM; targeting is different; triggers that are supposed to open doors or whatever don't work (possibly preventing you from finishing the level); any other discrepancies from the original.
  2. Until I find a suitable replacement for it, my ancient serial trak ball must work and work smoothly.  Modes of failure:  doesn't work at all or is "jerky" (smooth movement of the trak ball fails to translate into smooth movement on screen).  I concede that compatibility with this old hardware might be asking a lot, but hey—it works in Vanilla DOOM!
  3. I must be able to remap key bindings.  The trak ball lets me move and turn with great flexibility, but the home row keys for my left hand must be strafe left, fire, strafe right.
  4. It must be possible to make the graphics look good on my CRT.  Modes of failure:  gamma correction doesn't work; gamma correction works but the graphics still look dim or dingy.  So maybe DOOM was meant to be dark and dingy.  I don't care.  I cranked the gamma up to its maximum in the original and I want to do the same thing now.  (See notes about why gamma correction matters.)
  5. The aspect ratio of rendered graphics must be correct.  Mode of failure:  in part or in whole, the display is vertically compressed, resulting from a failure to correct the 8:5 aspect ratio of the ancient, oddball 320×200 mode used by Vanilla DOOM to the 4:3 aspect ratio that is now standard for the shape of CRT that I have.  This problem can be avoided by sticking with graphics modes that have an 8:5 aspect ratio.  The only standard alternative is 640×400, but 1024×640 or 1280×800 would probably work.
  6. There can be no glaring bugs that detract from gameplay.  Modes of failure:  rendering bugs (worse than Vanilla DOOM); clipping bugs (worse than Vanilla DOOM); hangs; crashes; settings that won't stick; broken or buggy sound.
  7. The original music had better work.
  8. It has to work under Windows XP or Linux; otherwise, I may as well run Vanilla DOOM.

Nice-to-haves

  1. PLUTONIA.WAD, TNT.WAD and the Icarus PWAD should play almost exactly as they did in Vanilla DOOM.  This would be a requirement if I had played those wads back in the day, but I didn't, so I would not notice if they played differently now.
  2. Screen resolution should be at least 640×400, preferably 1024×768.
  3. OpenGL would be nice.

Non-requirements

  1. 3-D sprites.
  2. Multiplayer.
  3. Exhaustive configurables for every possible gameplay nit—if these make it trickier to get full DOOM compatibility, then they are counter-productive.
  4. Ability to replace original music with ABBA.
  5. Ability to create or use new wads.
  6. True 3-D gameplay.
  7. Other Special Features that didn't exist in Vanilla DOOM.
  8. Compatibility with Heretic, Hexen, BOOM, or anything else other than Vanilla DOOM.

On gamma correction

DOOM existed long before there was an LCD monitor on every desktop.  The graphics were always too dark.  If you couldn't get gamma correction to work, everything was black.  But LCD monitors have an interesting flaw—they can't do black!  All dark colors are brighter than they would be on a CRT.  So, ironically, the infamously dark DOOM graphics look fine and dandy without a lot of gamma correction.

Most of the screenshots in these pages were taken while I was still using an old CRT, and not the brightest one ever made, so they might look overexposed on an LCD screen.

Other notes on DOOM lighting

DOOM's software renderer makes more distant objects appear darker, as if all light were emitted from the player.  This effect is usually eliminated in OpenGL ports.  While this makes everything look better, it unfortunately makes it impossible to see some "lighted corners" that are used to hint at the existence of a secret, such as the example from E2M2 shown below.  The extra lighting is only visible when the surrounding area is affected by distance-darkening.

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