Why do many cartridges require re-centering the screen?

[highinfidelity]

Please excuse the very trivial question; I'm almost sure that I'm the only one who doesn't know the reason, and quite surely it has been asked before.

Since when I was a kid I have always wondered why some VIC cartridges - mostly games, or perhaps all of them were games - require recentering the screen with cursor keys or joystick at startup. Is this just a "feature", or is it a necessity coming from a screen memory remapping or anything similar? I never had in my entire life a TV set in which the standard "framed" screen output by the VIC was even slightly off-centered: always well steady right in the middle, and I have always wondered why on earth anyone may feel the need to move it around. By the way in some of the games (Gorf comes to mind) only the very last rightmost position before the screen rolls back to the extreme left is barely acceptable, which of course was an annoyance and I have always wondered why it wasn't fixed or improved.

In some games, the screen could be centered only horizontally and not vertically (I don't remember any game that worked the other way around, that is re-centerable only vertically but not horizontally, but of course examples may exist that I'm not aware of). And finally, now that thanks to the FE3 I am exploring many carts that I didn't own, I have also found several games in which the screen will not re-center neither with the joystick, neither by pressing the cursor keys, and neither by pressing any other key on the keyboard at random. What's the matter with these?

[Mike]

See here, "Cartridge Game Picture Position out of place", and to quote from there:

[...] the PAL and NTSC versions of VIC-I have the relevant registers (XPOS, YPOS) at the same place, but they need different default values to correctly center the display window.

The KERNAL provides the correct default values in an init table at $EDE4. That is one of the reasons the VIC-20 KERNAL is different for PAL and NTSC! Other XPOS and YPOS values should be derived from that table, via offsets. That easily recenters the screen in case the display window is resized, but either noone told the cartridge writers about that table, or they didn't care.

Emphasis added.

[highinfidelity]

Ah, OK, thanks... I kinda figured there must have been a "natural" solution for this, as I don't recall any other home computer or videogame that required manually centering the screen (although they may exist some of which I'm unaware, of course).

So for the games that are "non-movable" the code itself should be changed, I suppose. There is no other simple way of dragging the screen around...

[Mike]

So for the games that are "non-movable" the code itself should be changed, I suppose.

That is what nbla000 did with all the cartridge images that went into Mega-Cart. They were either fixed to make them truly TV system neutral, or where not applicable, they are live-patched to suit the users TV system.

[beamrider]

So for the games that are "non-movable" the code itself should be changed, I suppose.

That is what nbla000 did with all the cartridge images that went into Mega-Cart. They were either fixed to make them truly TV system neutral, or where not applicable, they are live-patched to suit the users TV system.

Such attention to detail went into the MegaCart - that's why it's still King.

[highinfidelity]

Mmmmmmmmmh do you feel that the FE3 has been neglected, by comparison?

[tokra]

The non-patched ROM-images are causing so much confusion nowadays and Mega-Cart has been out-of-production for so long that it would be nice to have an archive of the patched Mega-Cart ROM-images for the affected cartridges. I realize that some of the images require code outside their own ROM-images because of space-issues. But at least for the other ones this would make it easier for other multi-carts to use them.

Of course, the original ROMs should be kept for historical purposes.

[beamrider]

Mmmmmmmmmh do you feel that the FE3 has been neglected, by comparison?

Well all the cartridge images are patched as per OT, MC has a nice case and box included and the menu is nicer IMO, but since you can't really get them any more this is all moot.

[nbla000]

That is what nbla000 did with all the cartridge images that went into Mega-Cart.

Yeah, it was a very big work...

Such attention to detail went into the MegaCart - that's why it's still King.

Thanks
But you have to see, the next coming revision...

MC has a nice case and box included and the menu is nicer IMO, but since you can't really get them any more this is all moot.

And don't forget music by Carlsson... however we never stopped production but since it is an hobby project, we have other priorities in the life sometime...

To stay on topic, when new mega-cart firmare revision will be released by me, I hope very soon, I will release also an external boot menu for all old mega-cart revisions, to automatically load from an sd2iec drives or pi1541 all new "reworked" items (about 150) with some additional plus, all centered for both PAL/NTSC systems.

Almost all these new items could be played from any vic with proper expansion (normally 32K) by using a standard CBM Drive too and why not... a tape.