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Chris
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Graphics Scrolling
Post Posted: Wed Jul 28, 1999 9:20 pm
How does a video game system make the screen scroll? Is it the hardware that does it or the software
that does it? And if it's the software, how does it keep track of the level positions and stuff? How does
it know when to draw the graphics and when to erase the graphics?

Also, with our modern day systems. Can our current monitors perform screen scrolls or does the software
have to do it? How could you get the same effect of scrolling inside of a Windows 95 form window?

Even though I've written games before, I've never had to deal with scrolling and I'm sick of creating
static games or mearly simulating it my moving images in one direction. I would like to be able
to design a huge level and be able to venture though it. I want my levels in Rollan Lightning
to be pretty huge. Enough to keep the player interested and feafull of suprise attacks from gunmen
and such. And I'm debating whether I should keep studying Z80 Assembler and write the game
for the SMS or just keep designing it for the PC in mind.

Chris :o)
 
  • Joined: 24 Jun 1999
  • Posts: 1732
  • Location: Paris, France
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Post Posted: Wed Jul 28, 1999 9:52 pm
Quote
> How does a video game system make the screen scroll? Is it the hardware that does it or the software
> that does it?

The hardware does it for most 8-bits and 16-bits console systems.

Quote
> And if it's the software, how does it keep track of the level positions and stuff?

It does even if the hardware do the scrolling.

[..]
Quote
> Also, with our modern day systems. Can our current monitors perform screen scrolls or does the software
> have to do it?

The software do it, although there is a way to do hardware scrolling on the PC (vertical only, I think) but it's tricky and not used or usable anymore.

Quote
> Even though I've written games before, I've never had to deal with scrolling and I'm sick of creating
> static games or mearly simulating it my moving images in one direction. I would like to be able
> to design a huge level and be able to venture though it. I want my levels in Rollan Lightning
> to be pretty huge. Enough to keep the player interested and feafull of suprise attacks from gunmen
> and such. And I'm debating whether I should keep studying Z80 Assembler and write the game
> for the SMS or just keep designing it for the PC in mind.

Depends. It will be probably harder to write it for the SMS, but you'll learn more.
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Eric
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SMS Scrolling Question
Post Posted: Wed Jul 28, 1999 11:34 pm
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> > How does a video game system make the screen scroll? Is it the hardware that does it or the software
> > that does it?

> The hardware does it for most 8-bits and 16-bits console systems.

How exactly does scrolling on the SMS work?

In SMSC's document, they claim that VDP registers 87 and 88 control horizontal and vertical scrolling respectively. But, what do the values written to those registers mean? Are they scrolling speeds, or simply offsets to shift the display?

It seems they should be offsets, let me assume that is the case for the following questions:

I know there's a screen mode where the left-hand column of tiles can be turned off. This would allow a small buffer for horizontal scrolling, but what happens if the horizontal scroll offset is greater than 8 (pixels)? The screen is shifted over more than the available buffer memory. What get's displayed?

Does anybody know how commercial software handles smooth scrolling?

Eric



If the VDP register scroll data represents offsets, what happens if the value is greater than 8? There's only 8-pixels of off-screen buffer available for horizontal scrolling.
 
Nyef
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Re: SMS Scrolling Question
Post Posted: Wed Jul 28, 1999 11:44 pm

Quote
> How exactly does scrolling on the SMS work?

> In SMSC's document, they claim that VDP registers 87 and 88 control horizontal and vertical scrolling respectively. But, what do the values written to those registers mean? Are they scrolling speeds, or simply offsets to shift the display?

> It seems they should be offsets, let me assume that is the case for the following questions:

> I know there's a screen mode where the left-hand column of tiles can be turned off. This would allow a small buffer for horizontal scrolling, but what happens if the horizontal scroll offset is greater than 8 (pixels)? The screen is shifted over more than the available buffer memory. What get's displayed?

> Does anybody know how commercial software handles smooth scrolling?

> Eric

> If the VDP register scroll data represents offsets, what happens if the value is greater than 8? There's only 8-pixels of off-screen buffer available for horizontal scrolling.

For all of these questions, I suggest looking at the source code to an emulator if you have such.

--Nyef
 
  • Joined: 12 Jul 1999
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Z80 all the way, man! *nt*
Post Posted: Thu Jul 29, 1999 4:48 am
I'd just like to say that KoRn kick arse.
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  • Joined: 24 Jun 1999
  • Posts: 1732
  • Location: Paris, France
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Re: SMS Scrolling Question
Post Posted: Thu Jul 29, 1999 9:20 pm
Quote
> It seems they should be offsets, let me assume that is the case for the following questions:

Yes it is offset.

Quote
> I know there's a screen mode where the left-hand column of tiles can be turned off. This would allow a small buffer for horizontal scrolling, but what happens if the horizontal scroll offset is greater than 8 (pixels)? The screen is shifted over more than the available buffer memory. What get's displayed?

The whole screen is wrapped (left<->right, up<->down). Four lines are permanently masked on the SMS, making like a "buffer" which you can use to store data which could be at the top or at the bottom after a scrolling change. Masking the first column also you to do the same thing, and it's being used by all games using horizontal scrolling, of course.

Quote
> Does anybody know how commercial software handles smooth scrolling?

First column in masked.
Each 8 pixels of scrolling, the first (masked) column is rewrote with what will come from the right (in a left to right scrolling game), then the scrolling continue and the gfx are shown, etc..
(sorry for the crap explanation. you know, my english sucks and i'm tired right now :)

Quote
> If the VDP register scroll data represents offsets, what happens if the value is greater than 8? There's only 8-pixels of off-screen buffer available for horizontal scrolling.

Wrapping.
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