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So, the watery HDMA effect...


jeffythedragonslayer

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The opening crawl to Ariel The Little Mermaid has the horizontal scroll of the background modified on a scanline-by-scanline basis to simulate a watery effect:

 

 

On the SNES, this is called HDMA and is accomplished by writing to the BGnHOFS PPU registers during hblank.  What's it called on the Genesis?

Edited by jeffythedragonslayer
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On 7/22/2023 at 6:58 PM, jeffythedragonslayer said:

The opening crawl to Ariel The Little Mermaid has the horizontal scroll of the background modified on a scanline-by-scanline basis to simulate a watery effect:

 

 

On the SNES, this is called HDMA and is accomplished by writing to the BGnHOFS PPU registers during hblank.  What's it called on the Genesis?

Well, HDMA is used on SNES to change the background(s) scroll value every scanline (or whatever amount of scanlines), but the effect itself is just line scrolling and done per scanline here, right. So, I would assume it's actually just called line scrolling on Genesis as it doesn't have HDMA but does have a built in ability to line scroll, row scroll, and column scroll that I assume are done as part of the normal DMA instructions. Although maybe there is a specific name for it on Genesis, I'm not sure, but line scrolling is what it is (at least that what I see it called usually anyway).

 

I expect someone will have mentioned it by name in the following link if it's not just called line scrolling though: 

http://gendev.spritesmind.net/forum/viewtopic.php?f=22&t=719

 

PS. It was that thread that actually got me to join that particular forum and create the following thread in response:

http://gendev.spritesmind.net/forum/viewtopic.php?f=22&t=3339

Edited by Kirk_Johnston
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  • 4 months later...
On 7/22/2023 at 10:58 AM, jeffythedragonslayer said:

The opening crawl to Ariel The Little Mermaid has the horizontal scroll of the background modified on a scanline-by-scanline basis to simulate a watery effect:

 

 

On the SNES, this is called HDMA and is accomplished by writing to the BGnHOFS PPU registers during hblank.  What's it called on the Genesis?

 Generically, it's referred to as "raster effects". SNES HDMA transfers are also "raster effects". On systems that use the interrupt method, a more specific name would be "h-int" or "hsync interrupts" or "horizontal interrupts".

 

Quote

so maybe there isn't any need for fancy terms like HDMA.

 There's no need to use the term because HDMA doesn't exist on MD (or almost any other system out there). Is the SNES the only system you'd dev'd on?

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38 minutes ago, turboxray said:

 Generically, it's referred to as "raster effects". SNES HDMA transfers are also "raster effects". On systems that use the interrupt method, a more specific name would be "h-int" or "hsync interrupts" or "horizontal interrupts".

 

 There's no need to use the term because HDMA doesn't exist on MD (or almost any other system out there).

Thanks.

38 minutes ago, turboxray said:

Is the SNES the only system you'd dev'd on?

No.

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On 7/22/2023 at 12:58 PM, jeffythedragonslayer said:

The opening crawl to Ariel The Little Mermaid has the horizontal scroll of the background modified on a scanline-by-scanline basis to simulate a watery effect:

 

 

On the SNES, this is called HDMA and is accomplished by writing to the BGnHOFS PPU registers during hblank.  What's it called on the Genesis?

It's weird seeing a Disney game that wasn't made by either Capcom or Virgin.  They didn't quite get the Disney style.

 

Anyway, the Genesis had 2 ways of doing HDMA effects.  The first is hardware line scrolling, which the Genesis had built in.  The second is IRQ interrupts, for everything else.

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2 hours ago, Aaendi said:

It's weird seeing a Disney game that wasn't made by either Capcom or Virgin.  They didn't quite get the Disney style.

 

Anyway, the Genesis had 2 ways of doing HDMA effects.  The first is hardware line scrolling, which the Genesis had built in.  The second is IRQ interrupts, for everything else.

Hardware line scrolling sounds like the better way, am I right?

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