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PostPosted: Thu Dec 18, 2014 5:48 pm 
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The top two tile rows can be specified to ignore horizontal scroll, and the right eight tile columns can be specified to ignore vertical scroll. They only ignore one of the scroll axes though as far as I know, so this means they're only useful for games that scroll in a single direction (on the other hand, this probably would have helped with the NES a lot if it had that feature...)

As for the Game Gear, well, remember it's basically just the center of the Master System window, so basically those two features end up off-screen and become useless. At least it has the sprite scaling bug fixed (which is why Virtua Fighter Mini takes advantage of it).


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PostPosted: Thu Dec 18, 2014 6:45 pm 
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Sik wrote:
The top two tile rows can be specified to ignore horizontal scroll, and the right eight tile columns can be specified to ignore vertical scroll. They only ignore one of the scroll axes though as far as I know

Well, this makes the first option pretty useless, since you could very easily mimic the effect with a mid-screen horizontal scroll change, without being restricted to a particular height or position for the status bar. As for the second case, yeah, it seems somewhat useful if you're only scrolling vertically.

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At least it has the sprite scaling bug fixed (which is why Virtua Fighter Mini takes advantage of it).

What sprite scaling bug? This games was ported to the Master System though (by TecToy, probably), wasn't it? What about Earthworm Jim on the SMS, which uses scaled sprites for its status bar? Do those games fail when played on certain SMS consoles?


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PostPosted: Thu Dec 18, 2014 7:00 pm 
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BTW, though I should mention an SMS game which used a creative solution for the status bar vs. vertical scroll issue: Ys

The words are sprites, but the meters are background tiles. Since they don't have any vertical details, they can be drawn taller than they need to be and only a section of each is displayed with raster effects. They always start and end at the same screen positions, but the actual tiles are scrolling vertically, which can't be noticed because there are no vertical details.

The same concept could probably be used for more complex status bars, if you used symbols instead of words to indicate what's being measured, and bars, squares, sticks, or anything else without vertical details to measure/count stuff.


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PostPosted: Thu Dec 18, 2014 8:00 pm 
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tokumaru wrote:
Sik wrote:
At least it has the sprite scaling bug fixed (which is why Virtua Fighter Mini takes advantage of it).

What sprite scaling bug?

Only the first four of the eight sprites on a scanline can be stretched horizontally. This bug is fixed in the SMS 2 and Game Gear. (Source, beginning at "sprite pixels are zoomed to double")


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PostPosted: Thu Dec 18, 2014 8:22 pm 
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tokumaru wrote:
Well, this makes the first option pretty useless, since you could very easily mimic the effect with a mid-screen horizontal scroll change, without being restricted to a particular height or position for the status bar.

Except for the part that you avoid having to set up a raster effect, which honestly is a hassle. I mean, what's easier, writing raster effect code that needs to ensure it fires in the correct line as well as undo its effect in vblank, or just setting a bit in a register and forget about it? =P

This is the same deal with the NES, where you need to do a busy loop with the sprite 0 collision flag in order to do a scroll split for a HUD like the one in Super Mario Bros. Want to bet it'd be much easier if it could have been done by just setting a bit?


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PostPosted: Thu Dec 18, 2014 8:36 pm 
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tepples wrote:
Only the first four of the eight sprites on a scanline can be stretched horizontally. This bug is fixed in the SMS 2 and Game Gear.

So Virtua Fighter Animation has glitched characters and Earthworm Jim has a glitchy status bar on a huge number of Master System consoles? how were games even allowed to use that feature?

Sik wrote:
Except for the part that you avoid having to set up a raster effect, which honestly is a hassle. I mean, what's easier, writing raster effect code that needs to ensure it fires in the correct line as well as undo its effect in vblank, or just setting a bit in a register and forget about it? =P

I do get your point, but personally, I'd rather go though a little more trouble if that meant more versatility (i.e. no size and position restrictions). If I realize that a 2-tile tall status bar at the top of the screen would look worse than a 4-tile tall one at the bottom, I would never settle for the former just because it's easier to implement.


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PostPosted: Thu Dec 18, 2014 10:16 pm 
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tokumaru wrote:
So Virtua Fighter Animation has glitched characters and Earthworm Jim has a glitchy status bar on a huge number of Master System consoles? how were games even allowed to use that feature?

The Virtua Fighter game is Game Gear only, so it never glitches. As for Earthworm Jim: the problem happens when there's over 4 sprites in the same line, so as long as you don't surpass this limit you're safe. (also if you wonder, this feature wasn't even added by Sega, it was inherited from the TMS9918 which originally had a 4 sprites per line limit, which is why the bug happens - Sega simply didn't take it into account)

tokumaru wrote:
I do get your point, but personally, I'd rather go though a little more trouble if that meant more versatility (i.e. no size and position restrictions). If I realize that a 2-tile tall status bar at the top of the screen would look worse than a 4-tile tall one at the bottom, I would never settle for the former just because it's easier to implement.

Yeah, but most developers who just needed a quick HUD and that were on a tight deadline sure would appreciate it =P


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PostPosted: Fri Dec 19, 2014 9:40 am 
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Sik wrote:
I mean, what's easier, writing raster effect code that needs to ensure it fires in the correct line as well as undo its effect in vblank, or just setting a bit in a register and forget about it? =P

What's easier: writing raster effect code once, or setting a bit in a register and then later having to write raster effect code when you port the game from the SMS to the Game Gear, which lacks this feature?

tokumaru wrote:
So Virtua Fighter Animation has glitched characters and Earthworm Jim has a glitchy status bar on a huge number of Master System consoles? how were games even allowed to use that feature?

By ensuring that the stretched sprites are frontmost.

Sik wrote:
most developers who just needed a quick HUD and that were on a tight deadline sure would appreciate it

That or just copy the HUD code from the same studio's previous project.


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PostPosted: Fri Dec 19, 2014 10:09 am 
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tepples wrote:
What's easier: writing raster effect code once, or setting a bit in a register and then later having to write raster effect code when you port the game from the SMS to the Game Gear, which lacks this feature?

When you're porting to Game Gear you're going to need a lot more than that since the screen is much smaller in the first place (to the point that you probably can't afford having a scroll-based HUD and you'll have to go with sprites instead).


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PostPosted: Fri Dec 19, 2014 8:20 pm 
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Sik wrote:
The Virtua Fighter game is Game Gear only, so it never glitches.

I'm pretty sure TecToy released a game called "Virtua Fighter Animation" for the SMS, and a quick search informed me that it's the same game. Was something relevant cut when Mini was converted into Animation?

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As for Earthworm Jim: the problem happens when there's over 4 sprites in the same line, so as long as you don't surpass this limit you're safe.

Have you even looked at the game before replying? It uses 8 scaled sprites in a row as an improvised status bar, on the GG as well as on the SMS.

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(also if you wonder, this feature wasn't even added by Sega, it was inherited from the TMS9918 which originally had a 4 sprites per line limit, which is why the bug happens - Sega simply didn't take it into account)

I see, but if they were aware of the bug they shouldn't have allowed developers to use it in Earthworm Jim.

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Yeah, but most developers who just needed a quick HUD and that were on a tight deadline sure would appreciate it =P

Could be, but that's why I said that I, personally, wouldn't settle for something less than ideal if the ideal is doable. Someone else under pressure might.


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PostPosted: Fri Dec 19, 2014 8:41 pm 
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Perhaps EWJ detects the original Sega Master System VDP (315-5124) and reverts to a simpler bar than it uses on the bug-fixed VDP in the SMS 2 (315-5246).

Vertical scaling apparently doesn't suffer from the bug.

How does the game look through a Power Base Converter? The Genesis VDP's SMS mode apparently doesn't support scaling at all.


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PostPosted: Fri Dec 19, 2014 9:03 pm 
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tepples wrote:
How does the game look through a Power Base Converter? The Genesis VDP's SMS mode apparently doesn't support scaling at all.

Nope, in fact that bit was replaced with the 128KB mode toggle (which switches the VRAM bus into 16-bit while in mode 5, albeit that's completely unusable on a stock Mega Drive which only has 8-bit VRAM). Why didn't they leave it as MAG in mode 4 is anyone's guess, they were probably making up space in the die (every other SMS2 improvement is retained as far as I know).

EDIT: oh also I just remembered, all PAL systems use the SMS2 VDP, so in theory PAL-only games don't have to worry about the scaling bug.


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PostPosted: Mon Dec 22, 2014 12:49 am 
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As long as we're thinking about Earthworm Jim for SMS, I have a hunch that it shares some code with the Game Boy version. The two look like they play similarly, and share a lot of low-res resources (with the GB ones at a lower depth).


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PostPosted: Mon Dec 22, 2014 5:45 am 
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Sik wrote:
EDIT: oh also I just remembered, all PAL systems use the SMS2 VDP, so in theory PAL-only games don't have to worry about the scaling bug.

TecToy releases were intended for PAL-M consoles, which are not really PAL. It's still possible that the consoles released by TecToy had the more recent VDP though, considering that since they only started making consoles a few years after it had already been released in other regions.


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PostPosted: Mon Dec 22, 2014 10:56 am 
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Well, later NTSC systems also had the fixed VDP, it's just that in those territories it was kind of useless since you couldn't rely on everybody having it. But on other places it was a safe bet, to the point that Codemasters would always use the 224 height resolution instead of the 192 one (I wonder if they were even aware that the 224 one wasn't present in all consoles).

But yeah, it's likely that TecToy's systems were using the fixed VDP. I'm not sure if they were using PAL-M though (Brazil is next to a PAL-N territory after all, many TVs were NTSC + PAL-N + PAL-M compatible, and they also sold consoles in Argentina which is a PAL-N territory).


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