Reverse engineering "Stack Light Rifle"

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Boojakascha
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Re: Reverse engineering "Stack Light Rifle"

Post by Boojakascha » Fri May 18, 2018 5:17 pm

Joefish wrote:
Fri May 18, 2018 5:10 pm
Can you point me to where the internals of the C64 one are documented? I can't find anything.
Never mind:
http://home.kpn.nl/bderogee1980/project ... Rifle.html
Exactly^^ you were faster, I was already writing this post.

I found PCB photos of the light pen of a competitor. This will be a good starting point for me =)
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Joefish
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Re: Reverse engineering "Stack Light Rifle"

Post by Joefish » Fri May 18, 2018 5:22 pm

Didn't realise the VIC20 / C64 hardware supports lightpen raster tracking as standard. I guess that did leave the Spectrum quite a way behind in lightgun technology, even given the same gun.
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Boojakascha
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Re: Reverse engineering "Stack Light Rifle"

Post by Boojakascha » Fri May 18, 2018 7:13 pm

Joefish wrote:
Fri May 18, 2018 5:22 pm
Didn't realise the VIC20 / C64 hardware supports lightpen raster tracking as standard. I guess that did leave the Spectrum quite a way behind in lightgun technology, even given the same gun.
I have read a book about ZX Spectrum pixel art. It seems the light pen was actually quite ok. Most people used a joystick or grid paper to draw nevertheless.
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Joefish
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Re: Reverse engineering "Stack Light Rifle"

Post by Joefish » Fri May 18, 2018 8:16 pm

When I have seen someone using a lightpen on a Commodore ( I think it was a Plus4) I remember some white vertical and horizontal bands sweeping the screen to locate the pen, then all the time it was drawing it threw up a large white square around the pen tip - presumably to track small movements, assuming the pen didn't jump outside that square from one frame to the next. But of course the white square obscured the immediate thing you were trying to draw.

It was also only good for drawing lines. If you jumped from one place to another (I can't remember if you had to tap a key or if the tip was a touch switch) it had to do the white bands to relocate you. I guess if the screen was mostly white it wouldn't have to, but if you were drawing on a mostly black screen it needed to flash up something bright.

Time Crisis on the PS1 would flash the screen white for one frame to track the gun; that's all it needed. On the calibration screen it left the screen pale yellow and could give you a live tracked cursor - though if you went over any of the darker markings on the calibration screen the cursor got stuck. I'm guessing the Commodore had a lot of jitter in its live tracking, and the software did a lot of averaging, so one bright flash frame of tracking data might not have been accurate enough.
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Boojakascha
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Re: Reverse engineering "Stack Light Rifle"

Post by Boojakascha » Fri May 18, 2018 10:03 pm

You are right, that's why commodore people used Koala touch pads instead to draw. A pity the pen wasn't good.

The NES Zapper is similar: It is just accurate enough to measure Y axis, but can't accurately measure x axis.

Some games flash blue instead of white, which makes it a bit less disturbing ;-) If designed well, a game wouldn't have to flash... but I see why they are doing it.
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