Real Interlaced graphics on the A8 - getting closer

[atariksi]

As I said before, you might be able to do the same on LCD TVs by just switching 2 frames.

 

A 40x50 type character mode would probably be best done by using the VScrol trick to create shorter characters.

 

e.g. you could still have 8x8 characters by having 2 character sets. The first has 4 lines per character representing scanlines 1,3,5,7.

The second has scanlines 2,4,6,8.

 

Swap charsets every frame. The resultant characters would have the same aspect ratio as Graphics 1 characters... except you'd have 4 times as many of them in the same screen area.

 

I think 80 columns is more useful than 50 rows. So perhaps having every other column in two charsets and turning down the chrominance should help give a 80*25 effect in Gr.0 with 8*8 or 8*16 chars interlaced. Shading helps as well so a backdrop of players for shading certain characters...

 

(I tried that interlace program with NTSC Commodore 1084 monitor and it did not work.)

 

I tried it with and without the following line:

 

45 POKE 16656,234:POKE 16657,234

 

Probably need to know the exact spot where to apply the VSync for NTSC...

[Rybags]

I've made a slightly improved version... will upload shortly.

 

I've also managed to reduce it to the simplest form, ie - lower the number of times DMACTL changes value.

 

I managed to get my newer TV producing interlace - only problem is it flashes background colours so I'm not going to call that a win.

 

Still plenty of possibilities - as is, I'm only changing DMACTL once per scanline straight after a WSYNC, there's other things that could be tried such as changing it at other times during a scanline.

 

NTSC... not sure if this routine as is would work anyway, since the OS VBlank routine might run too long. But I'm using Immediate VBlank, so you never know.

 

Here's a sample of the signal of the latest one. Cleaner looking VBlank, and it seems to be cut short in duration compared to a normal one.

 

Top graph = interlaced, bottom = normal

 

[Rybags]

INTEST4.zip

 

Here's the latest version with a few added features (BASIC required).

 

If running on NTSC, edit line 330 before running.

 

Change IF V>143 THEN V=130

to

IF V>130 THEN V=125

 

Remember to push "I" when the screen appears to turn Interlace on. Press it again if the screen becomes too garbled.

Press "F" to change field order if the diagonal line looks wrong.

 

Press "V" to change where the technique is applied (VCOUNT value). ed - You'll probably need to cycle through to value 134 on PAL before you get decent effect.

 

Press "R" to generate new DMACTL values (try once, then cycle through each VCOUNT possibility).

Edited January 22, 2009 by Rybags

[danwinslow]

Wow... is that Audacity? I had no idea you could use it for that but it makes perfect sense. How did you hook the signal to it?

[Rybags]

Just run the composite video signal in... or split the luma signal from S-Video.

 

Need a decent sample rate... 187,200 equates to 12 samples per PAL scanline.

Edited January 22, 2009 by Rybags

[danwinslow]

by 'in' you mean as in the microphone input?

[Rybags]

Prettywell any Line In.

 

I'd never thought of doing it, but a few years ago when looking for oscilloscope info, found stuff about using sound cards to do it.

[Rybags]

At last!

 

A stable interlaced picture without colour defects on my newish LG TV! Trying a slightly different approach to how I was doing things.

 

 

Slight problem still to iron out - I get one TV with a happy picture but the other one doesn't like it... needs some tweakage still.

[danwinslow]

Nice!

[MEtalGuy66]

Try doing a 40 column x 48 line text display with full 8x8 pixel characters..

[Rybags]

I cleverly blew a table away earlier... luckily I'd written the info down.

 

40x48 should be no probs... 80 columns would need bitmap mode though.

 

I'd like to try something like an APAC pic... should mean 80x200+ resolution there. Could probably do them in ~ 12K, just use the same colour data, and just alternate the luma data.

 

All this is dependant on if it can be gotten to run on all TVs... so far I've had success on both, but not at the same time.

 

I'll see later on about doing something like a 320x400 bitmap, just to see how it looks.

 

The thing with interlacing is that you need to be careful with single pixel horizontal lines... they flicker, you can't get around it.

[Urchlay]

40x48 should be no probs... 80 columns would need bitmap mode though.

 

...

 

The thing with interlacing is that you need to be careful with single pixel horizontal lines... they flicker, you can't get around it.

 

How bad on the human eye would the 40x48 mode be, you think? Bad enough that nobody would want to use it?

 

I've actually got an application (IRC client) that would benefit more from a 40x48 mode than 80x24, since most things people say in a chat are short (and often don't even fill up one 40-column line, even with their username prepended). Been playing with a 64x32 character soft (gr. mode using 5x6 character cells, which is surprisingly readable and not too slow, but of course eats 8K of RAM... if it were possible to do 40x48 using 2K or so, that'd rock... but not if it means giving my users headaches.

[carmel_andrews]

I cleverly blew a table away earlier... luckily I'd written the info down.

 

40x48 should be no probs... 80 columns would need bitmap mode though.

 

I'd like to try something like an APAC pic... should mean 80x200+ resolution there. Could probably do them in ~ 12K, just use the same colour data, and just alternate the luma data.

 

All this is dependant on if it can be gotten to run on all TVs... so far I've had success on both, but not at the same time.

 

I'll see later on about doing something like a 320x400 bitmap, just to see how it looks.

 

The thing with interlacing is that you need to be careful with single pixel horizontal lines... they flicker, you can't get around it.

 

 

 

 

 

 

If you did this with bob1200's upgrade would you get proper interlace....and flicker free as well (and much higher graphics rez)

 

Are you using a modified Gr.8 or Gr. 0

[Rybags]

IIRC, you can get similar modes to that for text on the PC... of course you're dealing with better monitors.

 

Heaven did that 40x40 (?) or similar mode some time back using the VScrol trick. It looks OK, and the characters on it are only 6 pixels high.

 

With interlace, you can have normal height chars that are 16 pixels high.

Or you can use VScrol tricks as well to get smaller heights. So, 40x48 characters would still be 8 pixels high.

[MEtalGuy66]

How bad on the human eye would the 40x48 mode be, you think? Bad enough that nobody would want to use it?

 

It wouldnt be bad at all.. Go use an AMIGA in hi-res/lace on a 1084(or similar) monitor. Its more than 80x48 (per screen) in most fonts.. And it's doing 640x400 (or better, depending on overscan) interlaced in NTSC..

 

Its not like any of the crappy "flicker modes" previously used on the ATARI..

 

The only place you really notice a flicker at all is on high-contrasting single pixel horizontal lines. Text looks great...

[perry_m]

If you can get 320x480 then you could do an 80 column font with a 6x8 pixel grid turned sideways.

I wonder how legible it would be. You would have to turn the TV/monitor on its side (or your head) to make use of it.

NTSC can't do 480 lines but 320x400 would be possible, that would give a 5x8 pixel grid.

[atariksi]

IIRC, you can get similar modes to that for text on the PC... of course you're dealing with better monitors.

 

Heaven did that 40x40 (?) or similar mode some time back using the VScrol trick. It looks OK, and the characters on it are only 6 pixels high.

 

With interlace, you can have normal height chars that are 16 pixels high.

Or you can use VScrol tricks as well to get smaller heights. So, 40x48 characters would still be 8 pixels high.

 

CGA->EGA->VGA when toward making chars better rather than having more so 80*25 (640*200) used 8*8 chars on CGA, 80*25 used 8*14 chars on EGA (640*350), and 80*25 (640*400) on VGA using 8*16. They centered it on VGA since it supported up to 640*480. Some hacks based on VGA standard char cell height allowed for 50 rows (didn't look that good on small monitors).

[Urchlay]

If you can get 320x480 then you could do an 80 column font with a 6x8 pixel grid turned sideways.

I wonder how legible it would be. You would have to turn the TV/monitor on its side (or your head) to make use of it.

NTSC can't do 480 lines but 320x400 would be possible, that would give a 5x8 pixel grid.

 

I bet the 5x8 sideways interlaced font would be unreadable (too many single lines). But turning the screen sideways is a good idea... without interlacing, using 5x8 at 320x200, that's 40x40 (or 5x6 for 40x53).

 

Scrolling the sideways screen might be a bitch though...

[UNIXcoffee928]

Back in the day, a company called "Radius" made Mac monitors that could swivel easily from landscape to portrait orientation.

 

Maybe you could DIY up something functionally like that with PVC.

 

My quick guess would be to check "Space Invaders" code for a routine that you can recycle for the new scrolling.

 

PS, you guys are doing some killer stuff! Excellent Experimental Method Science going on here!

[Heaven/TQA]

If you can get 320x480 then you could do an 80 column font with a 6x8 pixel grid turned sideways.

I wonder how legible it would be. You would have to turn the TV/monitor on its side (or your head) to make use of it.

NTSC can't do 480 lines but 320x400 would be possible, that would give a 5x8 pixel grid.

 

I bet the 5x8 sideways interlaced font would be unreadable (too many single lines). But turning the screen sideways is a good idea... without interlacing, using 5x8 at 320x200, that's 40x40 (or 5x6 for 40x53).

 

Scrolling the sideways screen might be a bitch though...

 

turning sideways screen sux... you can have the 40x38 for free without any flicker... and without using highres modes.

[+SpiceWare]

Back in the day, a company called "Radius" made Mac monitors that could swivel easily from landscape to portrait orientation.

For work I've got a Dell 2407WFP that swivels. I use the VGA input with my work laptop and the DVI input with my MacBook Pro. OS X recognizes it and gives a rotate option. The rotate option under XP isn't as easy to find, have to run the NVIDIA Control Panel instead of the Display Control Panel.

[Cybernoid]

I tried your intest4.bas with my NTSC machine and old-school capture card, with the line 330 edit

 

Here is the output without interlaced:

 

Here is the output with:

 

[Rybags]

Capture cards behave in different ways, some even have interlacing options.

 

Try "F" for field swap if the line looks broken like the second pic.

[Rybags]

If you did this with bob1200's upgrade would you get proper interlace....and flicker free as well (and much higher graphics rez)

 

What upgrade?

 

A quicker CPU will make no difference to this technique, and the flicker issue is inherent in practically any CRT TV or monitor when driving it with an interlaced signal.

[carmel_andrews]

Sorry, not bob1200s, clausb's video cartridge upgrade (which i thought bob1200 was helping with)