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Intellivision Graphics Glitch


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I found this glitch that I've been able to pull off on Bizhawk and jzintv emulators. It involves pushing any button to start the game, followed by the pause code (buttons 1+9) exactly two frames after letting go of that start button, and then unpausing the game. The result is a completely messed up set of graphics that will persist until you reset the game (see image 1 for input string and the result if successful).

 

The glitch seems to work with every game, but AD&D Cloudy Mountain is the only one I've found to have a potential use for it. When entering a mountain, the entire cave network is already visible, including items and ladders! (see image 2, note that I haven't moved; a quiver of arrows to the left can already be seen) I'm currently doing speedruns of the game, and being able to see things like this would significantly reduce the amount of guesswork involved in getting a fast time.

 

My question to you guys is can any of you replicate this on a real console? I must've tried hundreds of times on my INTV III, but have had no luck. Is it possible this might only work on model I or II, or is it just a glitch exclusive to emulated ROMs?

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Edited by TheWinslinator
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Update: ok, so I found it wouldn't work on many games actually (I had only tested the ones I'm familiar with which are mostly Mattel). It won't work on Burgertime, Buzz Bombers, Atlantis (IMagic), Dreadnaught Factor (Activision), Blockade Runner (Interphase), Lady Bug (Coleco), Tower of Doom (INTV Corp), and I can assume many others.

 

From this information, it looks like it should only work with Mattel games that have that standard olive screen with text at the startup. It appears pausing interrupts some sort of graphics change from the title screen to the ones used in the actual game. I don't know much about how the exec ROM works, but if it doesn't work on an actual Intellivision, could it mean the ROM I'm using for emulation is a bad dump?

 

Any button the game allows you to start the game with should work (using a side button, if allowed, is probably the easiest). My method on a real Intellivision is to push a side button with my index finger, and exactly two frames after letting go, attempt to press both 1 and 9 with my thumbs. Alternatively, pressing 3 and 7 to pause the game should also work. Unpausing you can do with any button.

Edited by TheWinslinator
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The Intellivision have 2 graphic mode. Graphic mode 0, colorstack mode, which is the glitch is showing. Graphic Mode 1, BG/FG mode which the game above need to be switched on. The mode needed to switch before it start drawing the screen, so unpausing probably skipped the mode change and run the game in graphic mode 0, and not graphic mode 1 which it needs to be. The glitch you tried with the game and doesn't work since the game run in graphic mode 0.

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The Intellivision have 2 graphic mode. Graphic mode 0, colorstack mode, which is the glitch is showing. Graphic Mode 1, BG/FG mode which the game above need to be switched on. The mode needed to switch before it start drawing the screen, so unpausing probably skipped the mode change and run the game in graphic mode 0, and not graphic mode 1 which it needs to be. The glitch you tried with the game and doesn't work since the game run in graphic mode 0.

Thanks for this technical info, it makes pretty good sense for what I'm seeing. I'm going to see if there are any other input combinations which can bypass the switch to graphic mode 1, and then test them on console. Still waiting for people to test the original method on Intellivision models I and II.

 

I've noticed with AD&D on Jzintv, once in a while the extended border for scrolling does not come on. I've never seen this on real hardware. These minor glitches could be unique to jzintv.

Could you elaborate a little more on that scrolling glitch? For instance, when did it happen (entering a mountain, etc.)? Asking because I might want to check it out.

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interesting but hmm...

 

i tried once (long ago) to use a different palette for ad&d in nostalgia, which makes the path also visible, of course it makes the game much easier.

 

to be honest no speed runs on my side, i play it recently still in beginners speed and when i move to the next skill level those dragons are already to fast and one dammit has no sound, though there is no way to be warned.

 

however, cheating is fine but kills the game, not that i like to spoil your fun, i'm a cheater myself.

 

what i learned from making the path visible is that i used for a seuck game myself a very limited screensize, it equals to this "blindness", enemies appear very late, almost to late to act on them.

 

one shouldn't kill the intelligent in intellivision, a simple but effective way to gain gameplay, random arranged tiles and limited view.

it's really the heart and soul of cloudy mountain.

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..

Could you elaborate a little more on that scrolling glitch? For instance, when did it happen (entering a mountain, etc.)? Asking because I might want to check it out.

When it happens it's for both the main map screen and inside the mountain. It's not a glitch I can reproduce on demand.
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