Would an accurate port of the original Xevious arcade be viable on the A500?

[Cris1997XX]

Originally Posted by metalion

I never thought an Amiga 1200 was in trouble to run Xevious, my humble MSX2 has a very good port, maybe the best port non emulated.

[ Show youtube player ]

Well duh, of course the MSX2 handles this game better. It's got flexible hardware sprites, smooth horizontal scrolling and a large color palette. For the Amiga, it's like trying to push a square peg through a round hole

[jotd]

great MSX port.

Also a lot of flickering when there are a lot of objects on screen.

As someone said, it probably has a lot of hardware sprites. The amiga can do games with bigger objects. A lot of small objects isn't ideal for the amiga.

But Xevious will run well on A1200.

[Cris1997XX]

Originally Posted by jotd

great MSX port.

Also a lot of flickering when there are a lot of objects on screen.

As someone said, it probably has a lot of hardware sprites. The amiga can do games with bigger objects. A lot of small objects isn't ideal for the amiga.

But Xevious will run well on A1200.

It has 8 hardware sprites just like the Amiga, but they're much better (They are not 1-bit for one thing). Some elements are also part of the background, which is a decent way of faking more complex graphics on such a limited machine

[jotd]

Also the MSX port is adapts to the machine it's running on: no OSD for scores, different graphics, different maps & enemy layout. It's really very good, it's true.

The Xevious amiga port attempts to be 1:1 like the arcade. And it's failing already:

- not enough colors for tiles (24 vs 16)
- not enough colors for sprites (there are more than 32 colors for the sprites only)
- not enough screen height (288 because screen is rotated vs 285 PAL)

And on ECS it will really be washed up... if something comes up. But on AGA it will look very much like the real thing. Fortunately the hardware wasn't used at its limits (it could have partial palettes of 8 colors per sprite among 128 colors! same for bg tiles which could have separate 4-color palette per tile, and fg tiles could also use the color they wanted).

I first started as 128 color playfield but after a while it became obvious that it would be too expensive to blit & restore backgrounds for so many objects. Not mentionning the OSD.

Be patient. This is going to happen.

[tcdev]

Originally Posted by metalion

I never thought an Amiga 1200 was in trouble to run Xevious, my humble MSX2 has a very good port, maybe the best port non emulated.

You have to appreciate that the MSX2 port was designed and written specifically for the MSX2. As @jotd mentioned, changes have been made to the game to facilitate that, such as removing OSD etc. So no surprise it runs well...

In this case the 68K core Xevious code is expecting the same hardware capabilities as the original arcade machine. The Amiga 'layer' must try to deal with those expectations by essentially "emulating" the arcade hardware - and it spends a lot of time trying to do just that.

If you took the core and modified it and the assets to better suit the Amiga specifically, you'd likely end up with better performance with less effort. But the idea of this exercise is to reproduce 100% the original arcade experience with no compromises on gameplay etc. I have no doubt @jotd will get it across the line!

EDiT: Actually more to this last point; it wouldn't actually be impossible to make some changes to the target (Amiga) without modifying the core at all. I'm thinking, for example, re-mapping the top and bottom of the OSD layer - ie. the scores and remaining Solvalous - to an area off to the side of the screen, like most other home ports. The core code would be totally oblivious to this fact. An interesting possibility... but again, not the aim of this exercise.

[jotd]

Originally Posted by tcdev

Actually more to this last point; it wouldn't actually be impossible to make some changes to the target (Amiga) without modifying the core at all. I'm thinking, for example, re-mapping the top and bottom of the OSD layer - ie. the scores and remaining Solvalous - to an area off to the side of the screen, like most other home ports. The core code would be totally oblivious to this fact. An interesting possibility... but again, not the aim of this exercise.

Yes, remapping first & last FG tile writes to somewhere else is possible and was actually done : the remaining ships are already shifted by a few pixels up else they're not entirely visible. Amiga max vertical resolution in lores is 285 not 288.


But putting stuff on the side is an extra effort because you can't use DIWSTRT/STOP to clip graphics (I had to do some sprite clipping in Pacman & MsPacman because of that).

[A500]

Originally Posted by jotd

Be patient. This is going to happen.

It's easy to be patient with all these updates and the very enlightening discussion going on. Thank you!

[jotd]

A500, this game isn't going to be for you Maybe if you change your nick to A1200 or A4000.

Today I worked on the game and made good progress again.

Here's what I commented in my python script which handles the graphics and the different palettes

    # now the color degrading for sprites
    # for the bozos who think that the amiga hardware is superior to Xevious hardware,
    # the used sprites with used cluts use more or less 51 different colors
    # because of dual playfield (AGA) we need to reduce that to 15 colors or even 14!
    #
    # if we do that brutally, that going to be all yellowish shit so
    #
    # 1) we remove colors that are used in andor genesis and bragza, we're going to use
    #    hardware sprites for those, with a completely different & independent palette
    # 2) player ship (solvalou) also has a unique color: remove it since it's also a sprite
    # 3) noticing that a lot of colors are solely used in solvalou explosion, just replace those
    #    (this isn't going to make a big difference). An alternative would be to use a sprite there too
    #    but it would have to be double height/width and all so not worth my time developing it.
    #

Just for people to understand: to get good colors & speed from an Amiga you have to work harder than on dedicated hardware.

When the arcade designers wanted to create a game, they chose the best hardware adapted to it and used it extensively. We are lucky that they didn't use more colors because they could have.

Of course why bothering with dual playfield which reduces to 16+15 colors (there's a transparent color on the second playfield), after all ECS is 32 colors, AGA is 256 colors but then you have all the background to manage when you"re pasting/erasing the sprites + the OSD

That makes a lot of blits with 7 or 8 bitplanes. I'm pretty sure that it wouldn't work with 40+ objects on screen, even small ones.

Xevious hardware couldn't even start to run F/A18 interceptor or even Virus because it's a 2D monster tile engine which works with fixed pre-drawn tiles. Amiga is more multi-purpose. For 2D those arcade machines were killers. Z80 sucked but the custom graphic chips were really something.

Just a quote from Mark documentation on the hardware:

Sprites
Xevious has 64 sprites consisting of 16x16 tiles, with 8 colours per pixel, which includes
transparency. Each tile has a 7-bit colour attribute which is used to index into a table of 8-colour
look up tables. Tiles can be flipped on X and/or Y axes.
Sprites can also be joined to form double height and/or width sprites. These sprites use contiguous
tile codes to form the composite sprite.
Sprite registers are split into three (3) banks of 64 2-byte registers mapped into CPU memory space.

So basically 64 sprites at the same time, 8 colors per sprite, separate palette for each sprite, 128 colors total. Just wow!

[Cris1997XX]

Originally Posted by jotd

A500, this game isn't going to be for you Maybe if you change your nick to A1200 or A4000.

Today I worked on the game and made good progress again.

Here's what I commented in my python script which handles the graphics and the different palettes

    # now the color degrading for sprites
    # for the bozos who think that the amiga hardware is superior to Xevious hardware,
    # the used sprites with used cluts use more or less 51 different colors
    # because of dual playfield (AGA) we need to reduce that to 15 colors or even 14!
    #
    # if we do that brutally, that going to be all yellowish shit so
    #
    # 1) we remove colors that are used in andor genesis and bragza, we're going to use
    #    hardware sprites for those, with a completely different & independent palette
    # 2) player ship (solvalou) also has a unique color: remove it since it's also a sprite
    # 3) noticing that a lot of colors are solely used in solvalou explosion, just replace those
    #    (this isn't going to make a big difference). An alternative would be to use a sprite there too
    #    but it would have to be double height/width and all so not worth my time developing it.
    #

Just for people to understand: to get good colors & speed from an Amiga you have to work harder than on dedicated hardware.

When the arcade designers wanted to create a game, they chose the best hardware adapted to it and used it extensively. We are lucky that they didn't use more colors because they could have.

Of course why bothering with dual playfield which reduces to 16+15 colors (there's a transparent color on the second playfield), after all ECS is 32 colors, AGA is 256 colors but then you have all the background to manage when you"re pasting/erasing the sprites + the OSD

That makes a lot of blits with 7 or 8 bitplanes. I'm pretty sure that it wouldn't work with 40+ objects on screen, even small ones.

Xevious hardware couldn't even start to run F/A18 interceptor or even Virus because it's a 2D monster tile engine which works with fixed pre-drawn tiles. Amiga is more multi-purpose. For 2D those arcade machines were killers. Z80 sucked but the custom graphic chips were really something.

Just a quote from Mark documentation on the hardware:



So basically 64 sprites at the same time, 8 colors per sprite, separate palette for each sprite, 128 colors total. Just wow!

OCS/ECS or AGA, I know this will be amazing! I might not understand all the technical jargon, but I can feel it with my sixth sense

[lmimmfn]

For the OSD would it be possible to multiplex the sprites or on the lines with the OSD to interleave the sprites? OSD on even, enemy sprites on odd lines? realise its messy and messes with framerate/visuals. Or maybe as its a vertical scroller put the OSD on left or right panels(realise it takes from arcade asthetic)

[Pyromania]

When’s this puppy coming out already.

[jotd]

about the bozos, a few months ago I was one, assuming tha 1982 hardware could not cope with so many colors & sprites... But I was wrong.

About a release date, I'd say beta without sound & a lot of glitches in one or 2 weeks.

[A500]

Originally Posted by jotd

A500, this game isn't going to be for you Maybe if you change your nick to A1200 or A4000.

Well, for this one I might actually change my nick as I'm a big Xevious fan And the HD of my A1200 is hungering for more bits and bytes to chew on!

[jotd]

here's a screenshot of the boss fight. 27 colors on screen (palette can have 40
+ colors now with sprites using their own palette) with huge boss real hardware sprite (4 AGA sprites total, 96x96)



Also sound is starting to work. Will post a video in a few.

[Pyromania]

Looking awesome, thanx! I always enjoyed this game in the arcades for some reason.

[saimon69]

Originally Posted by Pyromania

Looking awesome, thanx! I always enjoyed this game in the arcades for some reason.

Well, was one of the first of its genre in 1983 in example

[jotd]

I have zoned a preview version of the game. It doesn't fit on an adf because all of the sounds are samples ATM. But it may change

It crashes when encountering the big boss ship, it's expected. There are other issues, but the first levels are playable at least.

[zzbylu]

I love Xevious! Gameplay: [ Show youtube player ]

[MarkG]

will look forward to the final release. used to play this alot back in the c64 days

c64 version
[ Show youtube player ]

[Cris1997XX]

Originally Posted by MarkG

will look forward to the final release. used to play this alot back in the c64 days

c64 version
[ Show youtube player ]

Man, this could've been much better...even the music is at the wrong speed