How much can you cheat in vanilla Doom demos?

There appear to be some values which can be entered in a LMP tic, which are impossible to generate by recording normally (unless under certain conditions where applicable).

- walking speed (forward or side) shouldn't record larger than 50, unless the -turbo parameter was set.
- holding down the "fire" button in LMP files will cause that weapon to remain active even if ammo is out. This can't be recorded normally.Not vanilla?

Can demos played in vanilla Doom overwrite your save files? That's sick.

What else is there?

That second point - do you have a demo that proves it?

Well, scratch that. It only happens when Lee's modifications of weapon switching are activated, apparently. In vanilla mode, it switches regardlessly. So I'm going to strike that through. It might be the same infamous logic that's irresponsive to ammo updates before changing guns, which continues to happen in Eternity, but not in PrBoom+.

I've no idea why no-one's responding, maybe the thread title is misleading? What you want to know is what values in the LMP file can / cannot be achieved when playing normally, right?

[Experienced TASers correct me if I'm wrong]

• Forward / Backward - any value 1-50. Keyboarders can only get 25 or 50 (walking or running).
  
• Turning left / right - any value I think. Keyboarders get only either 3 or 5.
  
• Strafing - maximum is 50. If the player is turning, the maximum it reduced to 40. Not sure if you can physically strafe-50 right and on the very next tic strafe-50 left.
  
• Firing a weapon can be done on any tic, in any combination with the above (you can hold your fire key/button or your cat can sit on it, no problem). If no ammo, there's weapon switching.
  
• Use - can be done on any tic. In speedruns if you want to press a switch, you usually hold "use" for a few tics or press it repeatedly, pressing "use" for one tic only is possible, but let's say suspicious.
  
• Weapon change - no restrictions. If you don't have a weapon, there's no changing sequence.

So if you exceed the limits, say strafe 60 or something, you were definitely cheating (entering the values manually). If you stay within the limits, we usually cannot tell :-P

printz said:

Can demos played in vanilla Doom overwrite your save files? That's sick.

What do you mean?

vdgg said:

Turning left / right - any value I think. Keyboarders get only either 3 or 5.

Yes, the keyboard control has a restricted variety of turning angles, but I checked that my demos also have some TL1/TR1 and TL2/TR2 ticks, not only 3 and 5. And your demos too.

vdgg said:

What do you mean?

According to this (scroll down to the end of section 3.4.4), you can save games in demos, same as how you can pause. That sounds malicious! Fortunately MBF (at least) prevents that. I don't know if PrBoom+ does. Maybe elsewhere in the code?

Apparently the Hexen classes strafe faster than moving straight. Can you legally do the equivalent of SR50 in Hexen, by moving forward with the same force as maximum strafing?

EDIT: It looks suspicious and futile. The Hexen classes as defined in ZDoom (I hope it's good enough for reference) can strafe faster in theory, but all forces (side and forward) are actually capped to the maximum forward speed, so they'll never achieve that fast speed in strafing. So SR50 works even with just the keyboard in Hexen, but at the lower speed (max forward). Here's the vanilla Hexen code:

if (forward > MaxPlayerMove[pClass])
	{
		forward = MaxPlayerMove[pClass];
	}
	else if (forward < -MaxPlayerMove[pClass])
	{
		forward = -MaxPlayerMove[pClass];
	}
	if (side > MaxPlayerMove[pClass])
	{
		side = MaxPlayerMove[pClass];
	}
	else if (side < -MaxPlayerMove[pClass])
	{
		side = -MaxPlayerMove[pClass];
	}

printz said:
According to this (scroll down to the end of section 3.4.4), you can save games in demos, same as how you can pause. That sounds malicious!

I don't recall anyone using it maliciously, but it's useful because it lets someone reach a situation from where to play while seeing some quirk, bug or event.

vdgg said:

Turning left / right - any value I think. Keyboarders get only either 3 or 5.

Is there a hard limit on how much a mouse in vanilla Doom can rotate you per tic?

printz said:

Is there a hard limit on how much a mouse in vanilla Doom can rotate you per tic?

Judging from existence of mouse spinners for vanilla, no.

Segmenting is even possible with Vanilla Doom now that the -control argument is better understood.

Here's an example: