What machine= setting are you using, and what version of DOSBox is it?

machine=pcjr
DosBox version 0.65

Images are autoboot PC Jr Cartridges (*.jrc images). Additionally, changing the...

cycles=

...value has no affect on the jittering either.

-Trebor

Just wondering, what command in DosBox, or program, would let me play thiese pc jr files?

in dosbox.conf
machine=pcjr

and then inside dosbox
boot nameofimage

Curiosly, this doesn't work for me in that way.

Inside Dosbox, I first need to mount the dir with the images as c and only then can I boot them.

For example on my computer this doesn't work:
boot d:\spiele\dosi\pcjr\Dotcega1.img
(error: cannot open image d:\spiele\dosi\pcjr\Dotcega1.img)

But this does:
mount c d:\spiele\dosi\pcjr
c:
boot Dotcega1.img

(this is with both 0.65 release and CVS)

About the original problem:
flickering seems to be gone if the cycles are set appropriate,
maybe this works for you, too (setting the cycle count rather low).

I think the jitter is probably because the these games were programmed for the PCjr. as they would be on a console. This requires tailoring the game to the video timings of the display hardware. DosBox doesn't emulate the exact speed of the 4.77Mhz 8088 in the PCjr. or cycle-exact emulation of a PCjr.

wd wrote:

About the original problem:
flickering seems to be gone if the cycles are set appropriate,
maybe this works for you, too (setting the cycle count rather low).

I have a 2.8GHz P4.

I tried the following "cycles=" values:

1000, 350 (default for me), 250, 100, 50.

The lesser values do affect the game play speed @100 & 50, the sound is choppy and the screen scrolls *very* slowly. However, the jittering is just as bad just in a "slower" motion as well.

Going in the opposite direction @1000, game scrolls and plays very fast, and plenty of jittering at a faster pace.

-Trebor

Just out of curiosity, have you verified that the jittering does not occur in non-PCjr games running in non-PCjr mode in DOSBox on your system?

Maybe either you or wd could post your dosbox.conf and compare it to the other's to see what's different that could affect things.

HunterZ wrote:

Just out of curiosity, have you verified that the jittering does not occur in non-PCjr games running in non-PCjr mode in DOSBox on your system?

Maybe either you or wd could post your dosbox.conf and compare it to the other's to see what's different that could affect things.

No other games "jitter", only these Activision titles. It appears more like the screen does not "update" properly when scrolling vertically, then anything else. Harry's "jittering" when running horizontally is not nearly as bad, and may have been present in the original game as well (It doesn't even become apparent until you're pass the "inital" screens and actual get to the multiple platform parts of the game). However, the 'score' area (Bottom 1/3-1/4th of the screen) is extremely noticable in both titles - but does not occur in Pitfall II unless the screen is scrolling vertically. Even at the beginning 'swimming' boards in Pitfall II, the part where you need to drop down and extra level (scene with the small waterfall to the upper left) to pick up one of the beginning gold bars (Electric Eel swims at the top), you can see the score section start to jittter then as well, but the screen is barely even moving vertically then.

Again, interestingly enough, if you press forward in River Raid (Full throttle ahead), there is *no* jittering - It completely stops. It is present if you fly at normal/default speed, or pull back to slow down your speed.

I would love to see wd's *.ini as he was able to stop the jittering. I'm at work now so unfortuantely I do not have access to my *.ini file(s). However, later I'll post it/them.

-Trebor

Not sure what .ini files you mean, but the dosbox.conf was default besides
the cycles setting. River Raid doesn't work out of the box for me, as it
hangs in some in 0x200 loop or so, thus i used a debugger enabled
version (maybe that's why it works).

wd wrote:

Not sure what .ini files you mean, but the dosbox.conf was default besides the cycles setting. River Raid doesn't work out of th […]
Show full quote

Not sure what .ini files you mean, but the dosbox.conf was default besides
the cycles setting. River Raid doesn't work out of the box for me, as it
hangs in some in 0x200 loop or so, thus i used a debugger enabled
version (maybe that's why it works).

Sorry - my bad, I meant *.conf files Not *.ini...🤣.

I tried the default settings as well under 0.65 but the jittering is still there. However, River Raid works without any hanging for me. Interesting that it hangs for you, though.

Could you post your *.conf file or/and even the debugger enabled version which contains no jittering?

-Trebor

wd wrote:

River Raid doesn't work out of the box for me, as it
hangs in some in 0x200 loop or so, thus i used a debugger enabled
version (maybe that's why it works).

I wonder if this is because River Raid requires a joystick; I had the same problem (the game would hang) when I had joystick emulation in DosBox disabled, but it worked ok when I turned joystick emulation on. This was in the standard 0.65 release on Windows.

Harry's "jittering" when running horizontally is not nearly as bad, and may have been present in the original game as well

No, that wasn't in the original game. On a real PCjr there is no jitter in Pitfall II or River Raid.

> I wonder if this is because River Raid requires a joystick

I see, maybe they require different default-values for port 0x200
when no joystick is attached (did the pcjr have/always have a
joystick or comparable device?? I guess so).

About the jittering: i think it occurs because of their kind of
scrolling routines, they copy screen parts and update the screen
assuming that all is done before it's actually displayed. It can
be corrected by adjusting the cycles, but as you said it appears
again if you accelerate/brake. They don't revector any interrupts,
i just found a vret adjustment and some joystick polling. No idea
what's going wrong with their scroller, sorry.

wd wrote:

> About the jittering: i think it occurs because of their kind of scrolling routines, they copy screen parts and update the scre […]
Show full quote

> About the jittering: i think it occurs because of their kind of
scrolling routines, they copy screen parts and update the screen
assuming that all is done before it's actually displayed. It can
be corrected by adjusting the cycles, but as you said it appears
again if you accelerate/brake. They don't revector any interrupts,
i just found a vret adjustment and some joystick polling. No idea
what's going wrong with their scroller, sorry.

The jittering does not occur if you press forward (accelerate) - It stops. The jittering occurs when you coast at normal speed or pull back (brake).

I would love to see your *.conf file, if you could please post it. As well as the debugger version of DosBox where it does not jitter. I have tried values as high as 1000 (Game plays extremely fast) and as low as 50 (Game play extremely slow), the jittering remains present with every value. After the 1000 cycles, I would decrease by 50 (I.E. 950, 900, 850, and so on). The overall gameplay speed as well as jitter speed changes, but the same jittering problem remains, just at the speed of the scrolling (IE. Value 1000 has super fast game play with super fast jittering. Value 50, very slow game play, with very slow jittering).

My results have been that jittering is always present regardless of cycle value. It only changes in speed frequency. The faster the game scrolls, the faster the jittering. The slower the game scrolls, the slower the jittering. Again, the only time jittering stops is if you press forward; Cruising at normal speed or pulling back causes jittering, regardless of cycle value.

Interestingly, although the jittering does stop when pressing forward on the joystick (Acelerating), it always has the corrupt looking display when there is no jittering (Screen shots boot_004.png & boot_002.png from my original post - where there's an imprint of what the last scanline would look like if the graphics were not shifted a scanline up on the display). The clean looking screens (Screen shots boot_003.png & boot_001.png), never show if the screen is not jittering.

-Trebor

> I would love to see your *.conf file, if you could please post it.

load dosbox 0.65, type config -writeconf dosbox.conf

> As well as the debugger version of DosBox where it does not jitter.

It does occur there, too, i just didn't notice it before as i could not play
it, and adjusting the cycles removed jittering for the first game part.

wd wrote:

> I would love to see your *.conf file, if you could please post it. […]
Show full quote

> I would love to see your *.conf file, if you could please post it.

load dosbox 0.65, type config -writeconf dosbox.conf

> As well as the debugger version of DosBox where it does not jitter.

It does occur there, too, i just didn't notice it before as i could not play
it, and adjusting the cycles removed jittering for the first game part.

I'm sorry. I'm a little confused. The config file you are stating uses the default settings for DosBox. How fast is your machine? I have a P4 2.8 GHz. The default conf file gives a value of 3000 cycles. Way too fast for playing the game on my system. As I posted earlier, even a cycle value of 1000 plays way too fast. Normal game play speed seems to be a figure between 500-250 cycles for me. Additionally, as I stated earlier, anything really low in value (IE 50), the game is extremely slow with jittering still in place throughout the game. Also you stated adjusting the cycles removed the jittering for the first game part. What is that adjusted value?

Could you please clarify what you mean by 'the first game part', where adjusting the cycles removed the jittering? Unfortunately, the jittering appears thoughout the entire game for me. Even when the first "game start scroll" occurs at the very start of the game, where your ship flies from the black portion of the screen to the start of the level the jittering is still present. This is true with the default cycle value 3000 as well as 1000, and any 50 cycle decreased value thereof (950, 900, 850, 800, 750...50). Additionally, besides 'the first part' of the game, are you still experiencing jittering thoughout the rest of the game? Thank you in advance for your answers to the questions.

-Trebor

> The config file you are stating uses the default settings for DosBox.

Well of course the machine=pcjr and cycles are changed from the
default settings.

> Could you please clarify what you mean by 'the first game part', where
> adjusting the cycles removed the jittering?

When the joystick isn't touched, the airplane will fly half of the screen
and the game stops then until some button/direction is pressed. This
short part has jittering of the plane/status info at the bottom of the
screen only when the cycles are too high (greater than 500) or too
low (less than 400).

> are you still experiencing jittering thoughout the rest of the game?

Yes, i didn't notice it before because the gameplay didn't start as i had
no joystick attached. With the cycles at 500 it jitters when
accelerating/braking the plane. When just flying, it doesn't jitter with
cycles at 500.

wd wrote:

> The config file you are stating uses the default settings for DosBox. […]
Show full quote

> The config file you are stating uses the default settings for DosBox.

Well of course the machine=pcjr and cycles are changed from the
default settings.

> Could you please clarify what you mean by 'the first game part', where
> adjusting the cycles removed the jittering?

When the joystick isn't touched, the airplane will fly half of the screen
and the game stops then until some button/direction is pressed. This
short part has jittering of the plane/status info at the bottom of the
screen only when the cycles are too high (greater than 500) or too
low (less than 400).

> are you still experiencing jittering thoughout the rest of the game?

Yes, i didn't notice it before because the gameplay didn't start as i had
no joystick attached. With the cycles at 500 it jitters when
accelerating/braking the plane. When just flying, it doesn't jitter with
cycles at 500.

Cool. Thanks, wd! I really appreciate all your input. Hopefully, somewhere down the road this jittering issue will be fixed 😀

Thanks Again,
Trebor