Atari 2600 Space Invaders Flicker on Stella?

[12padams]

Here are my specs:

Processor: Intel® Core™ i7-5960X Processor (8-cores, 20MB Cache, Overclocked up to 4.0 GHz w/ Turbo Boost)
Memory: 32GB (4X8GB) DDR4 2133MHz SDRAM Memory
Graphics Card: NVIDIA® GeForce® GTX™ Titan Z with 12GB GDDR5 – Dual GPU Card

 

So I'm doing a series for YouTube where I play a game from each year on consoles (emulated) from 1975 to 2015 in chronological order. Just reached my 1980 episode and Space Invaders on the Atari 2600 got the most votes. I've never played this game before (at least on the atari 2600) so I just assumed that the flicker in the lazer cannon and bomb shots was normal. After uploading the video however someone was surprised that there was sprite flicker.

 

Here is a link to the video, Skip to 2:30 to see the flicker (which remains constant throughout the whole time I play):

 

It just seemed like a cool effect to me so I thought it was a part of the experience. It occurs whether or not I am recording and it also happens when I use DirectX or OpenGL for rendering (no difference). I Also had major flicker in Adventure when more than 3 objects were on the screen at once but I thought, once again, that was normal.

 

Not all games have flicker, Kaboom doesn't, Street Racer doesn't. Haven't really tested any others nor do I know much about how these games are supposed to run (never experienced the Atari 2600) apart from what I am seeing through the emulator.

 

Any Idea about what's happening here?

 

Thanks in Advance for your help

[Keatah]

Yeh that's pretty bad. And totally not right. The colors are off too. There should be some slight flickering in the shots. It should be faster and more like a shimmering effect rather than visible on/off on/off. And they should never disappear like in your vid.

 

Maybe you can play with glsync option in the video tab of Stella. Or manually set the framerate to 60. You can also try changing the flipping policy from Flip to Blit or the other way around. This is on your graphics card. Anti-aliasing can be an issue too. The graphics card can be interpreting the natural subtle flicker as something there and then not - thus upsetting the anti-aliasing. I assume you're using Stella emulatore, right? If not, you should be.

 

And be aware not all games have flickering. That's right Kaboom doesn't and Street Racer doesn't. Adventure can show a lot of flickering with more than 2 or 3 object on screen at once. I suspect you are seeing that one correctly.

[Rotgut]

And be aware not all games have flickering. That's right Kaboom doesn't and Street Racer doesn't. Adventure can show a lot of flickering with more than 2 or 3 object on screen at once.

 

 

It was the bank-switching technique Atari used to allow more objects to appear onscreen than what the system was originally capable of.

[12padams]

Thanks for the info guys, I guess this just reinforces the idea that emulation will never be perfect and that real hardware is the only way to go for a perfectly accurate experience. And yes, I was using Stella

Edited January 8, 2016 by 12padams

[Starman]

I'm surprised you're seeing that so late in Stella's lifecycle. I agree, it has to be a setting. I get slight flickering, but I never lose sight of the lasers.

[+SpiceWare]

It was the bank-switching technique Atari used to allow more objects to appear onscreen than what the system was originally capable of.

Space invaders is a 4K game, no bank switching involved. The use of flicker is separate from the use of bank switching.

[+stephena]

The lasers in Space Invaders do indeed draw at 30Hz, so when making a video you need to make sure that (a) you turn on video synchronization, and (b) that you actually capture the framebuffer at 60fps.

 

Stella (and the 2600 in general) is not like other systems, where you can enable frame skipping, etc to speed things up. If you don't capture all 60 frames per second, then in some games it will indeed look like some of the graphics are missing. The reason it's not as apparent on a real system/TV is that a TV tends to blend one frame with the next, and you don't see the flickering as much. There's a setting to enable that in Stella, called 'phosphor mode'.

 

Finally, I have a new phosphor mode (developed by T. Jentzsch) that will come in a future release of Stella that more accurately emulates this behaviour.

[+SpiceWare]

Any Idea about what's happening here?

 

Besides the chunky 40 pixel background, the Atari has 5 movable objects it can use to create the game screen:

• 2 players (known as sprites on newer systems)
• 2 missiles
• 1 ball

The players have a handy feature that allows them to be shown in duplicate and triplicate - put 2 players next to each other and set them to triplicate to get a total of 6 aliens across the screen. From my presentation on Atari homebrew games:

 

 

One minor problem with using duplicate and triplicate is the missiles are tied to the players - if a player is output using triplicate, so is the corresponding missile. Because of that, all shots in Space Invaders are drawn using the ball object. There's only 1, so flicker is used. The shots are staggered though so 2 shots can be drawn at a time, which limits the flicker to 30 Hz. You have to capture and show the resulting video at 60 fps in order to see the correct image.I think YouTube sometimes converts the video to a different frame rate, which results in the flicker you're seeing.

 

 

As a side note, you mention how ridiculous it is to have to hit GAME SELECT so many times to get to game variation 87. Just hold down GAME SELECT, the value will auto-increment. The value will increment even faster if you hold down both GAME SELECT and GAME RESET. As for why the game didn't have a menu, being so young you'll probably have a hard time believing it but ROM was a super expensive resource back then. Other than the 128 bytes of RAM, the Atari had no built in resources for the games to tap into, no character set graphics, no common subroutines (no BIOS) like you find in modern systems. As such, everything shown on screen must be in the game's ROM. As an example of how much room a menu takes, I put one in Medieval Mayhem. The graphics and code to show it took up 6K. ROM is cheap now so I had 32K to work with. Back then Space Invaders only got 4K. Asteroids was the first 8K game for the Atari, it came out the year after Space Invaders.

 

 

[12padams]

Wow, thanks for all that info guys! It makes me feel even more proud that I specifically promoted this forum in a previous episode. You guys are very knowledgeable and helpful!

 

Yea, at the time of the video I knew menu's were out of the question for the Atari 2600, I was just meaning to compared to todays standards such a system for selecting options is quite ridiculous however it was 1980, things were different due to primative computer technology back then.

Overall though this series I work on is focused on "look how far we have come!". Moving year by year closer to modern times and looking at how things have evolved. It really helps you appreciate modern games more. For example 5 years ago I looked at some atari 2600 games and thought... These are absolutely terrible! But through experiencing the Fairchild Channel F before the Atari 2600 I have grown to really appreciate the Atari 2600 due to its huge colour pallet (128 to compared to 8 on the Fairchild). 128 may be bad for todays standards but for me right now... it's not 2016. I've deleted my memories of modern games (at least during the series) and graphical upgrades on new systems are ground-breaking and amazing to me. In my world it's 1982 and I'm deciding whether to upgrade my Atari 2600 to a colecovision or an Atari 5200, I'm really excited for the release of these consoles soon! Through experiencing gaming from the very early days and moving forward, what once looked terrible to me (NES) looks absolutely incredible and AMAZING! Everybody my age (21) and younger should give this a go...

 

P.S. When you said space invaders was 4K I was literally like !!!! Not even the PS4 can do 4K resolutions yet! Then I realised you were referring to storage space and I laughed at myself