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Stern Electronics 'Rescue' & 'Minefield' Gradient Background
#332073 - 09/19/14 11:08 PM
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I've always been impressed by the graphics of these two games, although I never had the chance to see them in person.
My main question is for someone who has more technical expertise than myself and is purely for self interest. How did they accomplish the gradient background effect?
Being 1982-83 releases, it really seems innovative to have the smooth gradient backgrounds to set these games apart from their competition at the time. However, they seem to be the only games utilizing this type of hardware/software technology.
I don't see any artwork files associated with these games, so I'm making the assumptions that the gradients are created in video hardware.
Was their specialized hardware to display this type of smooth gradient? Was it a high cost?
I'm mainly asking as it adds a lot of depth (along with the parallax scrolling) to relatively simple games and you really didn't see this type of effect in that era outside of these two games.
If anybody knows anything about it more than me, I'd appreciate hearing your thoughts.
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Re: Stern Electronics 'Rescue' & 'Minefield' Gradient Background
[Re: Pr3tty F1y]
#332133 - 09/21/14 03:07 PM
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> I've always been impressed by the graphics of these two games, although I never had
> the chance to see them in person.
>
> My main question is for someone who has more technical expertise than myself and is
> purely for self interest. How did they accomplish the gradient background effect?
(Note that I lack any technical expertise, these are just my thoughts about this)
Looking at the source (http://git.redump.net/mame/tree/src/mame/drivers/scobra.c who said you can't look at the source in git?) I noticed that Rescue and Minefield have different video inits than the other games in the driver. The comments say that both use more palette for the backgrounds. Note that Rescue uses the same background colours twice, while Minefield uses two different gradients thus defines double the background colours than Rescue.
My guess is that while sprites and graphics used a limited palette to keep rom usage low, the background was generated programatically by the video hardware at very low rom space cost (I guess just defining the palette values somewhere).
Maybe someone more aware of how those things worked would say how close I am to the real thing. Close like the higgs boson or far like human teleportation and time travel? 
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| AWJ |
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Re: Stern Electronics 'Rescue' & 'Minefield' Gradient Background
[Re: Pr3tty F1y]
#332147 - 09/22/14 12:42 AM
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They could feed the bits of the horizontal counter (these are rotated games) directly into a resistor ladder DAC to produce the gradient. For the game that has blue on one half of the screen and brown on the other half, just use the high bit of the counter to switch between two resistor ladders. In either case, no additional PROMs would be needed.
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Re: Stern Electronics 'Rescue' & 'Minefield' Gradient Background
[Re: Pi]
#332210 - 09/23/14 01:20 PM
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> Looking at the source (http://git.redump.net/mame/tree/src/mame/drivers/scobra.c who
> said you can't look at the source in git?) I noticed that Rescue and Minefield have
> different video inits than the other games in the driver. The comments say that both
> use more palette for the backgrounds. Note that Rescue uses the same background
> colours twice, while Minefield uses two different gradients thus defines double the
> background colours than Rescue.
Looking at the source doesn't help you. That is how we draw the background, not how the original hardware draws it.
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| R. Belmont |
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Re: Stern Electronics 'Rescue' & 'Minefield' Gradient Background
[Re: AWJ]
#332218 - 09/23/14 05:05 PM
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> They could feed the bits of the horizontal counter (these are rotated games) directly
> into a resistor ladder DAC to produce the gradient. For the game that has blue on one
> half of the screen and brown on the other half, just use the high bit of the counter
> to switch between two resistor ladders. In either case, no additional PROMs would be
> needed.
Yeah, on hardware of that era that's almost certainly how it worked.
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