Advanced graphics programming techniques

[carmel_andrews]

I was 'trying' to read a thread on atariarea.krap.pl's website (their A8 forum), unfortunately google was very crap at translating the text into english ( as about 40 p/c of the text remained untranslated)

 

Anyway the thread in question refered to a technique for extending the vertical resolution of the A8 up to 240 pixels...using a modd'd Diplay list technique and something called 'JVB' (Jump to vertical blank i guess)

 

Anyway there seemed to be some 'disagreement' within the thread (from the little that was translated) as to whether this technique was possible

 

Since some of the Atariarea's polish contributors are active on AA (Atariage) perhaps they could shed some light on this and establish 'conclusibvely' if the little A8 is capable of a vertical resolution of 240 pixels

 

Just curios that's all

 

here's the translated link of the thread in question

 

 

http://translate.google.co.uk/translate?hl...iarea%26hl%3Den

[+CharlieChaplin]

Well,

as for a short answer: yes it is possible ! RIP uses 160x238 Pixels (since Antic has a bug and thus *full* 240 pixels cannot be used). Many other gfx formats use more than the standard ...x192 or ...x96 pixels vertically, the technique was once called overscan, you can see it e.g. in TIP pix (160x119), Technicolor pix (80x119 ?) and other gfx formats... -Andreas Koch.

[xxl]

> since Antic has a bug and thus *full* 240 pixels cannot be used

 

 

you can use 240 lines if there is no jvb in dl and last line is not hires. http://atari.pl/2test.obx try it on real atari.

[Heaven/TQA]

Thanks Jay Miner you simply extend your gfx display via display list... so no magic here...

[Heaven/TQA]

15 years ago I tried some "Atari ST" tricks to display stuff in "real overscan" area... so f.e. make a display list with has more than 240 scanlines (incl. the jmp instruction), the picture starts to roll... after a certain delay switch to a correct display list....

 

so... I managed to have an Antic 7 scroll line at top of the display in the top "border". but when I got a new TV set I realised that it worked only on the former TV because I timed everything on this device.

 

Did someone else tried something like this?

Edited July 25, 2008 by Heaven/TQA

[Rybags]

I don't think I've tried that.

 

I was always of the impression that Antic knows not to bother fetching DList outside the display area, even if you forget to code a JVB.

 

And, I also suspect (as we discussed in the thread I made some time back) that it's probably GTIA that causes the 240th scanline hires "bug". I think the best way to work out what's going on there would be to capture the outputs from AN0-AN2 with an external device and compare what happens between various displays -maybe Antic doesn't send a VBlank signal, or maybe it gets sent at the wrong time, or maybe something else goes wrong. Or maybe nothing goes wrong and GTIA screws up because it still thinks it's in Hires mode and gets it's knickers in a knot over that fact.

 

As for the 240-scanline thing, it only happens if hires is on the last scanline so 239 lines is fine. I tried to get effects by doing stuff like turning DMA off mid-scanline and I think I did some stuff with V/HScroll but couldn't get anything funky.

 

I also tried alternating between a 239 and 240 line display to see if you could get proper interlace but needless to say that didn't work either.

Edited July 25, 2008 by Rybags