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- Dwedit

#1 2021-10-21 5:40:05 am

Registered: 2021-10-21
Posts: 2

How to "extend the background layer"

I found this message on a... less reputable forum that I shouldn't and won't link to and wonder if anyone knows how to achieve this?:

playing Metroid 2 on my GBA flash cart meant running it on a GB emulator made for the GBA because that voltage thingy
so one feature was it could extend the background layer to the edges of the screen
this meant you had like "long range radar" for the cave walls so you could see where the f*** you were, but only short range radar for monsters so you still got the jumpscares
made it a lot more enjoyable for me

If it's possible through emulation on Windows that would be very cool indeed. 8)
Many thanks for any ideas. :)


#2 2021-10-21 5:44:20 am

Registered: 2021-10-21
Posts: 2

Re: How to "extend the background layer"

I should say, I've tried emulating a GoombaColor ROM with both an original and modified Metroid II ROM on Visual Boy Advance - M and tried the original ROM on that emulator. I did fiddle with VBA-M and Goomba's settings too without any luck.


#3 2021-10-21 2:03:40 pm

From: Chicago
Registered: 2004-12-12
Posts: 1,004

Re: How to "extend the background layer"

Old Goomba used four background layers:
- One layer for the GB's background
- One layer for the GB's Window
- One layer for the UI
- One layer for the Border, this also acted to mask the screen to the GBC's screen size.
Old Goomba had a feature where you could simply turn off the Border layer, and everything behind it would become visible.

But this approach doesn't work for the Game Boy Color.
A GBC background layer needs 3 components to draw it on a GBA: The background layer itself, a layer for the Color Zero tiles, and a layer for the High Priority tiles.  Without the "Color Zero" tiles, you'd see the background color instead of Color #0 from all the other palettes.  Without the "High Priority" tiles, sprites appear in front of tiles that are supposed to mask them.

So Goomba Color possibly could need up to 8 layers at once:
- Background Tiles
- Background Color 0 Tiles
- Background High-Priority Tiles
- Window Tiles
- Window Color 0 Tiles
- Window High-Priority Tiles
- UI
- SGB Border

A GBA only has 4 layers.  So depending on what the game or emulator is doing, it has to pick 4 of those possible layers to show on the screen.
Most GBC games do not show a Background and Window side-by-side on the screen at the same time, so they only need 3 layers.  This leaves one layer free for a SGB border, or for the UI.  (If the SGB border and UI are enabled at the same time, the High Priority tiles are sacrificed)
But if a GBC game needs to show a Background and Window side-by-side on the screen, the emulator will sacrifice High-Priority tiles in order to show the Color 0 tiles correctly.

Then there's the other task: cropping the GBC game on a GBA screen.
Old Goomba used a background layer for the border to cover up everything.
Goomba Color used the GBA's Window feature to clip the GBA background layers and sprites to be within a rectangle area.

So basically the background layer system is much more complicated for Goomba Color.  There's no "border layer" to simply disable and see behind everything, because the Window feature is used to perform clipping instead.

Could disabling clipping be done?  Maybe, I just never considered it when I developed the background layer selection system.

"We are merely sprites that dance at the beck and call of our button pressing overlord."


#4 2022-03-24 6:17:16 pm

Registered: 2007-06-09
Posts: 5

Re: How to "extend the background layer"

Dwedit wrote:

Could disabling clipping be done?  Maybe, I just never considered it when I developed the background layer selection system.

Very weird...I could've SWORN I did this years ago and never released it...but I searched everywhere on my computer, and all I could find was a filed called "goomba_color_test.gba" which is just Goomba 2.36 with a few GBC ROMs in it. And no source anywhere. What the heck?


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