Things about Doom you just found out

Jimi said:
There's a transparent pixel in the Baby Spiderdemon face! Well, actually it seems there are a bunch of transparent pixels in the Baby Spiderdemon sprites in various places where there shouldn't be transparent pixels.

Unless you're talking about another pixel, that is not a clear pixel, just the practice in many tools to color the background with index 247, which is shown as cyan in those tools but is black in DOOM and is used in various graphics. This is why I use tools that allow you to set the index and color of the background. In the DOOM IWADs, index 255 (RGB 167/107/107) isn't used in graphics and unlike cyan (which has nothing to do with DOOM internally), it isn't a glaring color and contrasts well with the images. I'm guessing they reserved the color as the background for editing when they made the game. Supporting this theory is that it's a unique color that isn't part of any range, and it's at the end of the palette. In the vanilla game, color 255 is only used for the dots in the frame rate meter when developers mode is enabled, if I'm not mistaken.

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myk said:

Unless you're talking about another pixel, that is not a clear pixel, just the practice in many tools to color the background with index 247, which is shown as cyan in those tools but is black in DOOM and is used in various graphics.


If you look at the arachnotron sprites with SLADE 3 (which, contrarily to SLumpEd, definitely does not assume index 247 or any other in always transparent), and use a very contrasting background color, you'll see there are true transparent pixels.
Affected are BSPIA3A7, BSPIA4A6, BSPIA5D5, BSPIB1E1, BSPIB2B8, BSPIB4B6, BSPIC2C8, BSPIC3C7, BSPID3D7, BSPID4D6, BSPIE2E8, BSPIF2F8, BSPIF3F7, BSPIG4G6, BSPIH1, BSPIH4H6, BSPII6, and BSPII7.

myk said:

In the DOOM IWADs, index 255 (RGB 167/107/107) isn't used in graphics and unlike cyan (which has nothing to do with DOOM internally), it isn't a glaring color and contrasts well with the images. I'm guessing they reserved the color as the background for editing when they made the game. Supporting this theory is that it's a unique color that isn't part of any range, and it's at the end of the palette.

It's also quite explicitly used as the transparent color in some of the Doom alpha picture formats.

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Discovered this thanks to Sodaholic's obsession with pixel-precise rendering, though I had stumbled upon in when analyzing the linuxdoom code: the fuzz column effect (partial invisibility) is not applied to the top and last lines of the screen buffer, regardless of resolution (there's even an explicit check to limit column draws outside this range). This isn't changed even in e.g. prBoom and prBoom+ (dunno about ZDoom though).

There's a good reason for it, though: since the fuzz effect actually "samples" pixels from the left and right of the screen, applying it on the first and last line risks reading beyond the screen buffer. It's possible to fix without complicating the rendering code too much, but probably not worth it (well, unless you're Sodaholic ;-)

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Gez said:
If you look at the arachnotron sprites with SLADE 3 (which, contrarily to SLumpEd, definitely does not assume index 247 or any other in always transparent), and use a very contrasting background color, you'll see there are true transparent pixels.

Yeah, I think I was looking at BSPIA3A7 in XWE, which evidently fills empty (surrounded) pixels with color 247. I guess those pixels had color 255 on them...

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Yea, they're transparent in the game too, which is where I actually found it, then I found more transparent pixels in Slade.

Recently I also noticed that the spikes on Imps are slightly inconsistent on their locations/appearances. For an example the knee spikes disappear in TROOL0.

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In DOOM version 1.1, if monsters hurt themselves with barrels, if they have a melee attack, they kill themselves. If they don't have a melee attack, they just shoot blindly, trying to kill themselves.

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It's perfecly possible to use all 256 colors in a sprite with transparent regions, but most current Doom spriting tools ("current" might mean "dating back to 1994", in some cases) can only use 8-bit images as an input, and have to sacrifice 1 arbitrary color in lieu of using a proper separate transparency map or accepting images with e.g. 257 colors or an explicit alpha channel.

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Jimi said:

Yea, they're transparent in the game too, which is where I actually found it, then I found more transparent pixels in Slade.

Recently I also noticed that the spikes on Imps are slightly inconsistent on their locations/appearances. For an example the knee spikes disappear in TROOL0.


You have been TROOL3d by sprites.

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Maes said:

It's perfecly possible to use all 256 colors in a sprite with transparent regions, but most current Doom spriting tools ("current" might mean "dating back to 1994", in some cases) can only use 8-bit images as an input, and have to sacrifice 1 arbitrary color in lieu of using a proper separate transparency map or accepting images with e.g. 257 colors or an explicit alpha channel.

That's why you should use SLADE 3.

In fairness, it probably wouldn't run on 1994 hardware.

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I just found out about the switch that raises up the imp-soulsphere trap in map12. I figured you had to deal with the imp ambush no matter what, and the soulsphere was like compensation for it. I think I might have found out about this earlier, but I most certainly forgot until just the other day.

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Bashe said:

I just found out about the switch that raises up the imp-soulsphere trap in map12. I figured you had to deal with the imp ambush no matter what, and the soulsphere was like compensation for it. I think I might have found out about this earlier, but I most certainly forgot until just the other day.

Have you ever checked the wall beyond the teleporter in the lowering-platform blue key room? That switch raises it as well. Then, you're able to get by the ambush: kill the revealed imps, go into the teleporter and obtain the Soulsphere with no injuries.

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Barrel graphic is 32 units tall, but the hitbox for barrel is 42 units tall. Feels a bit like a typo in the settings...

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Cell said:

Have you ever checked the wall beyond the teleporter in the lowering-platform blue key room? That switch raises it as well. Then, you're able to get by the ambush: kill the revealed imps, go into the teleporter and obtain the Soulsphere with no injuries.


Hah,. I was always playing this level by getting there by teleport and killing the imps. And then I wondered what that button in the blue key room does. So one could just play more clever, drop into that pit with the ammo box and lost souls, finish all the rooms, go to the key and press the button, come back again, kill the imps from below and then retrack back to the teleport that makes you get the blue sphere. Kinda more timewasting, not the usual way to go, just why I missed this idea, but I should try.

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Gez said:

It's also quite explicitly used as the transparent color in some of the Doom alpha picture formats.


Actually from what I recall that color being explicitly used in the Alpha versions is because Carmack hadn't figured out a sufficiently elegant way to determine the end of a post (column of pixels in a graphic) yet. So the result was that most of the alphas used that color to indicate to the renderer that the column has explicitly ended

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I was transcribing some of D_E1M1 in Sibelius for my own amusement yesterday -- I wanted to experiment with the bassline a bit. It suddenly hit me like a ton of bricks why every remake, cover and precedent of it just doesn't have the same groove. The track is stylistically in several pies; it's rock, with a textbook rock beat, that's played like heavy metal but in 12-bar blues form. The main motif has all the grungy hallmarks of metal, but with one difference: in each pair of low Es, the first is half the duration of the second. In the context of heavy metal, that sequence should be interpreted as a palm-mute, then an open bottom E. That's what makes it a bit fruity, because it diverts the focus from the tonic/root note (which is like 'headbang HQ' for any rock/metal track) to the melody (which itself is ambiguous because it barely falls on the beat). The natural inclination in metal is to palm-mute both bottom Es to emphasise the melody.



The groove I can't escape hearing is one of lurching/hanging over the beat. It's a technique I think Bobby Prince played around with further in D_E2M2. I believe he described it as a car going out of control...?

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0_o You learn something every day. I'm guessing you're referring to "The Demons from Adrian's pen" when you talk about the car comparison: it does have quite the interesting progression, doesn't it?

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Obsidian said:

I'm guessing you're referring to "The Demons from Adrian's pen" when you talk about the car comparison: it does have quite the interesting progression, doesn't it?


It really does. The whole ambience of it overall conveys shellshock/nausea to me. I hear a car going out of control when he puts the drums in retrograde around 1:11 - 1:34. Makes me think of the first time I saw the convulsing human torsos the Strogg reappropriated for their machinery in Quake 4... it'd be a total mindfuck to listen to if you were high.

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I'm not sure if this has been touched on here, but whatever. The BFG and Plasma projectiles have the same speed, but the rocket is slower, and the player can outrun the rocket if done right.

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In Doom, hit detection considers players and monsters to be a square, not a circle. This leads to a very interesting property:

A player's hit-box is 32x32 when looking at the map. This means that if you attack a player while facing north, south, east, or west (as hallways are typically aligned), you have a hittable area that is 32 units wide, as seen by the red part of the hit-box in this first pic:



However, if you attack a player while facing north-east, north-west, south-east, or south-west (as one might when using SR-50 in a hallway), you have a target that is 45 units wide. This is because two sides of the player's hit-box are exposed. This forms a right triangle with 32 unit sides and a hypotenuse that is 32*sqrt(2) = 45 units, as seen in this second pic:



My gut feeling is that when players feel swing-shots are more effective than normal shots, it is because they tend to fire while facing their target at a 45 degree angle during their swing. This makes the hittable target 40% wider and a lot more effective.

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I noticed that there's a Berserk flagged for multiplayer skills 1-3 in E1M1. It was a random BFG Edition coop with someone who couldn't feel up to change the difficulty from HMP to UV. Thought it was an exclusivity for that port until I opened the level with editor and saw that Berserk there. Mind was blown in that day.

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Opening the automap seems to subtly alter st_arms. At least in vanilla and chocolate-doom.

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Hmm, yeah, that's really strange. Some darker gray pixels seem to get drawn there. Once you go to the automap, it doesn't change anymore, even if you go full screen and back to screen blocks 10. It does get "cleaned" when you enter a new level, until you activate the map again.

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Re: E1M1,

it's not at all long ago since I discovered what the switch in the first room actually does. Ever since I first played the game, I thought it was that switch that activated the lift by the shotgun. It was only within the last year or two that I realized it actually opened up a door into the outdoor area. For whatever reason, I never, ever spotted that door before.

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Randy87 said:

Opening the automap seems to subtly alter st_arms. At least in vanilla and chocolate-doom.


Holy shit, well-spotted. Can anyone explain what causes this? I can only put it down to some subtle palette change caused by activating the automap, because the IWADs only include one instance of ST_ARMS.

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EvilNed01 said:

Re: E1M1,

it's not at all long ago since I discovered what the switch in the first room actually does. Ever since I first played the game, I thought it was that switch that activated the lift by the shotgun. It was only within the last year or two that I realized it actually opened up a door into the outdoor area. For whatever reason, I never, ever spotted that door before.

Same here. I think one time I actually caught the door going back down, but didn't realize that it had opened because of the button.

Speaking of E1M1 secrets, I still don't know how you're supposed to figure out the Imp pillar secrets on your own.

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(empty) said:

Speaking of E1M1 secrets, I still don't know how you're supposed to figure out the Imp pillar secrets on your own.


Where the Shotgun is hidden? Until I started being lazy and used map editors, simple curiosity and exploration is how I found secret areas. Sometimes it pays to backtrack through levels and listen for any platforms/doors.

In this case I guess one scenario would be if a player ignored those two Imps (because there's seemingly no way for them to follow, they pose little threat) and continued on to the exit area, only to have those same two Imps suddenly open the door and attack from behind while he's pre-occupied using Barrels to splat some Zombiemen. Naturally you'd want to go back and see where those Imps came from/how they got down, and so on and so forth. A SECRET IS REVEALED! *obnoxiously loud noise*

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BaronOfStuff said:

Holy shit, well-spotted. Can anyone explain what causes this? I can only put it down to some subtle palette change caused by activating the automap, because the IWADs only include one instance of ST_ARMS.


Also happens when you pick up different weapons -
most likely due to lazy updates of the hud gfx.

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_bruce_ said:

Also happens when you pick up different weapons -
most likely due to lazy updates of the hud gfx.


The plot thickens! I can't believe I never noticed this oddity in all the time I've played.

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I never open up the original IWADs to look for secrets. It makes finding new secrets all the more exciting. I'm sure there's a shit ton of areas in Doom 2 and Final Doom's that I haven't found yet. I did find the E1M1 shotgun secret on my own, but that was by genuinely playing and replaying the map specifically to figure out what does it.

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