Flickery Graphics

[snicklin]

I *think* I've seen contradicting information about flickered graphics or I have misunderstood what I've read. I'd just like to clear this up in my mind

 

Is it possible to alternate on-screen colours each VBI to produce a non-flickery output? OK, yes, it will be flickering, but I am talking about detectable flickering?

 

I thought that I'd read somewhere that certain colour combinations would mean that there would be no flickering (detectable by the average human being). Is this the case or is it a case that those colours only minimise the flickering?

 

I'd just like to know whether it would be possible to create a gr.12 game with more than 5 colours which did not flicker to the human eye?

[Xuel]

peteym5's RPG uses alternating ANTIC 4 screens and the flicker doesn't seem too bad.

[kenjennings]

...

 

Is it possible to alternate on-screen colours each VBI to produce a non-flickery output? OK, yes, it will be flickering, but I am talking about detectable flickering?

 

I thought that I'd read somewhere that certain colour combinations would mean that there would be no flickering (detectable by the average human being). Is this the case or is it a case that those colours only minimise the flickering?

 

 

Yes. It's not the color so much as the brightness/contrast. Two colors of approximately the same brightness merge nicely. Two colors with vastly different brightness levels will show flickering.

 

Don't let the luminance value of the color register fool you. Two different colors using the same luminance value are not necessarily the same brightness.

[Synthpopalooza]

There are some tricks that will minimize flicker.

 

For example, in Super IRG, you can do a checkerboard dither pattern, to blend colors on alternate frames. The effect looks alot better than full-screen flicker.

[Synthpopalooza]

There was also this game, originally designed by Itay Chamiel using COLRVIEW mode, a triple RGB flicker Antic 4 mode. I modified it to instead use ICE CIN lo-res ... by altering the GTIA register each scanline between normal Antic 4, and GTIA mode 11. This allows for 60 colors onscreen. It does flicker some, although it is less noticeable on NTSC Ataris.

 

http://atariage.com/forums/topic/211412-the-wall-v-20-tetris-using-ice-cin-mode/?hl=+the%20+wall%20+cin

 

And I also did a sample mockup of a Rainbow Islands screen using Super IRG as well. The results were very nice, I thought ...

 

http://atariage.com/forums/topic/202803-anyone-ever-thought-in-ways-to-get-rainbow-islands-on-a8/page-2?do=findComment&comment=2600221

 

The important thing to remember, is you do not have to double-buffer the screen here. Screen memory is the same as a normal Antic 4 mode, you just need space for two 1,024 byte fonts, and you switch the CHBAS (756) register every VBLANK to create the effect.

Edited January 21, 2015 by Synthpopalooza

[snicklin]

peteym5's RPG uses alternating ANTIC 4 screens and the flicker doesn't seem too bad.

 

I've just checked this out (albeit with Altirra and frame blending) and this looks acceptable to me as I (personally) cannot detect any flickering with this.

 

So it is possible to produce games with more than 5 colours without annoying the users.

 

Some games I cannot play because of the flickering, though I thought that Space Harrier handled it well to me with the fast action on the game screen.

 

I was wondering if there was a level of flickering which I could introduce into a game without annoying users. It seems that this is the case.

 

Thanks everyone else for your replies, tips and pointers to other works. Rainbow Islands looks good, is it just a mock-up or a serious attempt at a game?

[Synthpopalooza]

Just a mock-up at the moment, my programming skills are not that good. Was hoping someone else might take it up.

[Synthpopalooza]

Also, another trick to reduce flicker in Super IRG ...

 

Unlike the Space Harrier game, there are no color register changes in Super IRG. This means that you can use the same color on both frames and there will be no flicker. You want to use these primary colors for most of your graphics, and use the blended colors as supplemental colors. You can get 10 colors here, and an additional 4 colors when you use inverse (ATASCII>127) characters in Antic 4.

[phaeron]

(albeit with Altirra and frame blending)

 

Keep in mind that this is not a very good way to evaluate flickering displays since you're actually having the emulator remove the flickering entirely. The main reason for this option is for cases where it isn't possible to frame-lock the display and the flickering would be much more objectionable, such as PAL on a 60Hz display. It's important to actually see the flicker in action to see if it will be objectionable.

[Synthpopalooza]

It's also best to test on real hardware as opposed to an emulator. Disabling frame blending in the emulator doesn't always give an accurate flicker result, because the refresh rate of the monitor is faster than 50 or 60 hz, which results in some frames being dropped or improperly rendered.

 

Also keep in mind, these sorts of modes look better in NTSC because of the faster 60hz refresh rate.

[snicklin]

I've recently shipped all my Atari stuff over to Australia and all my things are stuffed away in boxes packed together at my in-laws house where I'm staying.

 

Unfortunately I'm unable to dig them out and test on real hardware, but I appreciate the comments that using emulators isn't the best option.

 

As I'm unable to look at real hardware currently, would people suggest that watching the flicker on an emulator without frame blending or with frame blending is closest to the real deal?

 

Or would it then just be a case of

a) My refresh rate

b) What is being displayed...

 

which are too many variables to know?

[Synthpopalooza]

Displaying your flicker on an emulator without frame blending will get you reasonably close to the real thing, you'll be seeing dropped frames occasionally. Altirra is the best emulator for this of course.

 

Also when testing it this way, you will want to change your video settings between PAL and NTSC, to get an idea how the graphics will look in both settings. NTSC will give better results, as I have mentioned, because it refreshes at 60 fps vs the slower 50 fps on PAL systems. So if you can get it to look reasonably good at the PAL setting, you are in good shape.

 

I've used this method alot in my own flicker-mode experiments.

 

Also, as someone mentioned above, you will want to try to keep your luminances no more than 1 or 2 steps from each other for best results. In Super IRG, setting your luminances about halfway is a good idea. You can get away with a greater variance, if you use that blended color sparingly.

Edited January 21, 2015 by Synthpopalooza

[ac.tomo]

There are actually a few ways to get extra colour on-screen in mode 15 without resorting to alternate frame methods; this has been documented before & it is in "the complete & essential map for the Atari xl/xe" located in one of the book archives online somewhere, just google it.

Anyhow, the easiest way to get more colour is to plot 2 different colours directly above & below each other and the visual effect will result in a new colour being visable, you can perform this exact procedure, starting on even scan-lines & starting on odd scan-lines and you will get a different colour again. What I do is to set all the colour registers to primary colours at the same lum & you then can get about 10+ colours, a few more if you use graphics 12.

Another method would be to create a display list alternating between a GTIA mode & graphics 15, obviously alternating a DLI on every scan-line to set the hardware register of location 623 correctly, this way I would pick maybe the 16 colour GTIA mode, and set the mode 15 registers to 3 or 4 different luminances, so therefore when 'bleeding' (or rather pal blending) takes place you will be able to get 16 colours & 4 shades of each colour.

Edited January 21, 2015 by ac.tomo

[Synthpopalooza]

The only downside is of course, you have a 96 vertical resolution. But it's an excellent solution for more than 4 colors in mode 15. And used in Antic 4 mode, you can have 23 colors onscreen at once thanks to inverse chars/PF3.

 

I also did some experimenting, with a 15+10 blend, shaking the screen up and down repeatedly by 1 scanline every cycle to give the illusion of 160x192 resolution at 30 colors, but using only 8K screen ram.

 

http://atariage.com/forums/topic/197450-mode-15-pal-blending/?p=2616560

 

Apparently these examples flickered more on a real atari (especially 50hz PAL) ... but the idea is swapping 15 and 10, no color changes except for COLBAK, which alternates between the BG color on mode 15 and a 9th color on mode 10 lines. Solid non-flicker color bands can be had by blending the same PF color on both lines, and a dithering pattern can be used when mixing different PF colors. It is also necessary to shift the mode 15 pixels one color clock right to correct for the mode 10 pixel shift.

Edited January 22, 2015 by Synthpopalooza

[snicklin]

Now the number of options are opening up!

 

So here is my game (as many of you have seen before). I want a non-flickering game but maybe with a few more colours available.

 

 

So I've been advised to keep the mixed colours to the areas that are non-predominant. Therefore I would like apples in some of the trees and some strawberries in the bushes.

 

I don't need a mass of extra colour, just a few more colours. As we can see, the screen is quite static and it is a graphics 12 screen.

 

Which method would people advise? I really don't like flicker though. I'd probably prefer to stick to gr.12 though and not start mixing gr.15 in.

[kenjennings]

Looks nice..

 

Since the screen is largely static the graphics/color flipping should work well. Using two shades of green for each page you can get a nice gradient in the trees and still have two more colors (and the mixing of those colors) available.

With DLIs you can play with one or both of those other colors at various vertical positions on the screen.

it looks like you're already using a DLI to change one of the tree hilight colors?

[Synthpopalooza]

Super IRG will work nicely in this game. With your 3 basic colors of red, green, and blue, blending these with the black bg color every frame gets you darker shades of each color. So, for example, you could use 2 level green shades on the trees. Mixing your primary colors adds yellow, magenta, and teal to the mix. And if you use inverse, the pf3 color gives you 4 more combinations.

 

Can you post up your font file? I want to play with this in my ICE font editor and see what I csn come up with.

[snicklin]

it looks like you're already using a DLI to change one of the tree hilight colors?

 

Ken,

 

Yes, I am amending the one colour to complete the colour scheme down the screen in order to give extra colour. I just need a bit more freedom in the placement of my extra colours.

 

Synthpopalooza,

 

I have PM'd you the file, I don't want it out in the open due to ABBUC rules. Thanks for your help!

[Heaven/TQA]

hey... game looks good!

[ac.tomo]

Yes, the game looks good. Mixing the colours the way I mentioned earlier is by far the better way especially if all you need is a couple of extra colours, perhaps beside primary colours bring in a couple of different shades, you'll be surprised at what you will get. This way, you won't get flicker at all & you don't need to do any extra DLI's and no pixel shifting is necessary either. As for the resolution, you will still be able to access all 192 scan-lines, and since your coloured area's will more than likely be bushes or so then vertical detail I don't believe is very important, not that you won't get this either, but using this method basically allows you to have 5 colours (in mode 12) throughout all the 192 scan-lines, but when obtaining the extra colours, that's when it will take 2 scan-lines in order to obtain any of the extra colours.

Edited January 23, 2015 by ac.tomo

[Irgendwer]

Which method would people advise?

 

Before adding colours, you could enhance visualization by introducing more variety and exploit existing colous as far as possible by using dithering techniques:

Uses only 22 different characters and the 5 out of the box colours.

[snicklin]

 

Before adding colours, you could enhance visualization by introducing more variety and exploit existing colous as far as possible by using dithering techniques:

Bildschirmfoto vom 2015-01-24 17:30:48.png

Uses only 22 different characters and the 5 out of the box colours.

 

This looks really good! I am no graphic artist (which is evident) but I like what you've done.

 

There's a couple of reasons as to why there isn't much variety in what I currently have....

 

a) The alphabet and numbers are inside my font using up plenty of useful characters. I will extract them out in time.

b) I've used repetition to allow the level files to compress well.

 

Perhaps with (b) I can come up with some special rules like "no tree can be followed by the same tree" or something like that and then altering the output.

 

Synthpopalooza is currently looking into some colour schemes for me (and has some nice work done already) so I'll await the final results there.

 

I may be able to combine some of yours and his work into the graphics. Lets see.

 

Thanks for that, it looks much more professional, "Druid" like with the dithering.

[snicklin]

hey... game looks good!

 

Thank you! And hopefully it will get a bit better!

 

Currently this is the state of the project:

 

* Level up on pressing fire button (for testing) is crashing the game when it didn't previously - this is being debugged

* Title screen created with a nice animation and a new song from Miker. Text corruption to be removed.

* "Drunkenness" factor being considered for addition. Horace is drunk. Being drunk creates unsteady movement and incurs optical illusions. Mirages caused by the drunkenness will be present. This could either be obstacles that are not obstacles really or rooms linking to rooms that they shouldn't.

* Currently considering auto-created levels from algorithms.

* New enemies, perhaps a worm or a snake. But it has to be things that exist in real life, the game is intended to represent real life to some extent.

* Puzzles

* Cleanup of the file system ongoing. There's too much redundant material in there.

* A stereo is on the ground. Touching the stereo will allow you to turn the music on/off.

[Creature XL]

 

This looks really good! I am no graphic artist (which is evident) but I like what you've done.

 

 

If I may say, you should definitely get a graphician, maybe Irgendwer volunteers

It makes a big difference. And personally, when I spend my time coding a game I would like it to look (and sound) good as well.

[Island2Live]

Hey snicklin,

 

I am reading this thread now since you started it and it gives me lot's and lot's of ideas how to do things. Thank you for that!

 

I've also had a look at RPG from peteym5 which is astoundingly flicker free despite the fact he does not use close luminance values when overlaying the screens in flicker mode. The answer to this is simple: Today we are in the world of relative slow LCDs which helps to blend the two frames. Don't know about plasma TVs and other technologies. But LCDs are slower in reaction time of their pixel than good old CRTs.

 

Have a look at those old »S.A.G.A.« text adventures (the ones with graphics not the text only versions). They also use a flicker method to produce more colors. I recall a visible not very nice flickering on my old Sony TV. It is gone on my Toshiba flatscreen TV and on my PC screen when using Altirra.

 

Just my two cents.

 

Kind regards,

Henrik (Island2Live)