Ghostbusters (Activision)

[Rob_hawk]

Looking great Chris and yes green is the way ahead for the ghosts I feel on the capture screen

[ChrisB]

I've been working on the capture screen. You can place the trap and move the men into position. Press L to move to each stage. I've also rearranged the colours on the screen to allow the beam effect - hopefully that will be next. Ghost movement is placeholder at the moment.

Also in the version I've changed the map ghosts to be white to make them more visible. This has also been applied to the car screen which makes the ghost hard to see against the white car. I've changed the colours of the lines to be yellow at the same time. Thoughts on these changes would be welcome. Both colour sets are independent so I can change on or both back.

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[tricky]

I like my slimers green

[fwibbler]

Had my first look at this today. I always thought the BBC could do a good version of this.
Its looking really good, with each stage looking colourful and slick.
I've only ever played the ZX Spectrum version and the Sega Master system versions.
As you probably know, the Master system has extra features over the other 8bit versions. Are you planning to include any of those?
Also, does this require any sideways RAM?
Looking great.
Cheers!

[lovebug]

looking fantastic, congratulations

[ChrisB]

Each of the versions has their own quirks and variations so although my main inspiration is the C64 version it's not going to be a direct conversion. At the moment I wasn't looking for the extras in the master system such as the stairs and the mid game shop.

At the moment - it doesn't require sideways RAM - although I'm down to about 4K free. Current plans are for a base and enhanced version with the enhanced version playing samples. Depending on how memory goes that might also include a different/enhanced ending screen.

In other news the beams are not working as I'd hoped so I will look to do an alternative....

[Cybershark]

Each of the versions has their own quirks and variations so although my main inspiration is the C64 version it's not going to be a direct conversion. At the moment I wasn't looking for the extras in the master system such as the stairs and the mid game shop.

The stairway section just seems impractical to program (for such a short segment that can only potentially be played once per game). I do think that the C64/Spectrum ending sucks though, without the film's "big boss fight", and Gozer and The Terror Dogs - now there's a band name - not even getting so much as a mention. So I'd definitely vote for the Master System ending - memory permitting. It just seems like such a rip off to repetitively play through all those samey levels and then to not have the payoff of taking down The Traveller!

[fwibbler]

What annoyed me about the stairway part was how tough it was to get through. I hardly ever got to the final part of the game on the Sega

[ChrisB]

It just seems like such a rip off to repetitively play through all those samey levels and then to not have the payoff of taking down The Traveller!

Or you could get the amstrad version that just went to a text screen as soon as you got past marshmallow man! I was not looking to implement a "showdown" but I am thinking about trying to fit in the end scene. I wonder if you could have a small amount of interaction to actually cross the streams and therefore close the gate - as opposed to it being a "cutscene"... Anyway - long way to go until then.

[ChrisB]

Beams!

This version adds beams - they don't do anything to the ghost and you can't cross them yet...

The beams are my own routine rather than taking something from one of the other versions - it also seems to be one of the most variable elements. At the moment they are quite wavey - I'll see how this looks when it comes to moving the ghost around. Comments welcome!

Both the ghost and beams are plotted using exclusive OR to the screen. The ghost uses the top bits of the byte and the beams use the bottom bits. I've therefore set the palette up to provide contrasting colours for the beam and a solid colour for the ghost. The intention is to provide less contrast for the ghost if you don't have the image intensifier.

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[ChrisB]

Now with gameplay!

I've more or less implemented the capture mini game. As this is (more or less) the only gameplay there is in the game comments on how it plays/feels are appreciated.

Points to note:

• The action key sometimes takes a while to register - I'll look at that later.
• Backpack power is not decreased so they last for ever.
• Only one man dies when you cross the steams.
• It's possible for the men to walk into each other with unpredictable results.
• At the moment the trap reverses as soon as it captures a ghost. Don't know if I like this.
• After you have won/lost nothing happens - press B to move on to the next screen and try again.

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[bob147]

Just want to say that I'm enjoying this dev diary. Always interesting to see you hit these decision points where you have to drop something due to memory constraints or whatever it is and seeing your process for deciding what to keep. It's really starting to come together now

[Rob_hawk]

I had a run through at the weekend and it really is coming together very well. I like the streams and the ghost trap, perhaps a delay or some small animation when it’s trapped would be cool however I know memory will be tight!

My original and favourite version was the C64 back in time but it’s so good to see this version shaping us so well.

[ChrisB]

In terms of memory - at the moment I have about 3.3K free. There is a significant piece of sprite graphics to add (marshmallow frames) but otherwise - as far as I know - the graphics are there so most of that space will be for code. I'm mostly going to concentrate on getting the gameplay in then add "flourish". Having said that attached is an updated version that animates the ghost after you fail to capture it - which probably counts as unnecessary .

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This version also improves the scroll text. It has gone from 4 pixels every other frame to 2 pixels every frame. The scrolling is a software scroll moving the bottom line left by a byte at a time - I keep thinking this might work better as rupture using hardware but I can't quite get my head around the memory layout for that.

In any case since it's mode 1 this will still only scroll 4 pixels at a time without some very "tricky" techniques. I've therefore used the palette to move to two pixels. Rather than simply plotting on half of a letter I plot that half in colour 1 then OR in colour 2 two pixels to the right then use palette switching to "move" the letters between whole byte moves. A picture to demonstrate:

Colour 1 is red, 2 green and 3 white. The top line shows all three colours as plotted then the second and third lines show without colours 1 and 2 respectively. So setting colours 2 and 3 then 1 and 3 to the same colour moves the letters two pixels to the left. Obviously the plot routine is more complex and takes a little more time - but it's a lot less that having to perform bit manipulation on the whole line! This looks best on the map screen at the moment as there is some unnecessary plotting going on when displaying the capture screen.

[tricky]

That does look a little tricky

[ChrisB]

After a brief distraction with scrolling text I've been tweaking the capture screen. Changes for this version are adding the backpack power mechanic (this is reset every time you enter the screen) including reduction of power and failure condition if it reaches zero. You can see the backpack on the status scroll (space). Trap and Men numbers are not updated as yet. I've also updated the logic so the beams are removed when the trap is fired as per the C64 version. Lastly both men now die if you cross the streams.

I'm now starting to focus on the map screen - and the logic of the city. The only visible difference at the moment is dots are drawn on the map as you move. Next will be stopping the ghosts moving if you drive over them. Currently about 3.1K free.

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Edit:Forgot to mention also changed the trap behaviour to continue to the top of it's path when it captures the ghost. To my mind this looks better.

[ChrisB]

This version allows you to go to buildings. The map display is just for demo purposes at the moment so there is always a ghost present when you enter a building. However backpack power carries over from one to the next. Go back to GBHQ to refill it. Traps and Men are not tracked. Also ghosts will stop when you move over them (this is slightly too generous at the moment) and will need tweaking. 2.9K free.

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[fwibbler]

This is looking really good.
I have a couple of thoughts:
On the road section, the ghost look very large when they scroll down the screen. I would suggest that ghosts the same size and style as those on the map screen would look better.
Also, on the road section, the road scrolls very slowly. Can that be sped up a bit?
Finally, on the ghost section, a couple of times I pressed the button to activate the trap and nothing happened (although I've just seen you mentioned that a while ago)
Cheers!

[ChrisB]

The road section hasn't been touched since the proof of concept. Yes - the intention is to go faster (and speed up and slow down).

The double height ghost on that section is what the C64 does - Here's a comparison.

[Rob_hawk]

I thought the road section was pretty faithful to the C64 which I’ve always preferred. It’ll be great once it’s speeded up a bit. It’s all coming together nicely.

[Cybershark]

Just looking at the C64 comparison screenshots, I wondered if a "grey" road might better suit? Here's a mock-up

I guess that doesn't work so well for a lo-res mode, and would just make for unnecessary coding really!

[tricky]

It wasn't very popular when I was going to do it in mode 0 for my port of sprint

[tnash]

But do you design for an old CRT running via an RF cable where the grey stippling will blur and look great, or for an (almost?) pixel-perfect rgb2hdmi / emulator on a modern screen where it's going to look like a chessboard?

Maybe Chris can code it as an option for the user if he has enough bytes and is willing?

Just looking at the C64 comparison screenshots, I wondered if a "grey" road might better suit? Here's a mock-up


gbroad.jpg


I guess that doesn't work so well for a lo-res mode, and would just make for unnecessary coding really!

[ChrisB]

It's an interesting question. On the map screen I'm using Cyan/Red dithering as it seems less harsh than black/white - although under b-em's "PAL" emulation it produces nasty banding so there might need to be an alternative there in any case... It is more complex for the driving scene because I'm using a special palette (see https://www.stardot.org.uk/forums/viewt ... 85#p401585) to prevent redrawing so there isn't room for a dithered background.

[Kecske Bak]

Software Invasion's "Attack on Alpha Centuri" used green and magenta stripes for "grey". On a CRT it looked absolutely fantastic.

[tricky]

I think a couple of the dithers work ok in my Pacman, but one is obvious but it is only a small area and I wanted people to be able to tell them apart as they have different personalities!

[RobC]

It is more complex for the driving scene because I'm using a special palette (see https://www.stardot.org.uk/forums/viewt ... 85#p401585) to prevent redrawing so there isn't room for a dithered background.

Maybe it could be done in a NuLA version?

There was a magazine game that used flashing colours (possibly at 25Hz) to create a sandy colour. I'm not sure it would be as effective over a large area though.

It is looking really good - my daughter played the latest version on Friday and really enjoyed it.

[ChrisB]

I'm not fan of rapidy flashingly colours. A NULA version is certainly a possibility - There are a lot of greys in the original.

Attached is an new version. This version takes the placeholder flashing blocks on the map screen and actually codes some gameplay mechanisms behind them. E.g. a building will turn magenta if you drive past it if it's about to flash red. Also red buildings time out and move on. If you leave the map screen and return the same building(s) will be flashing. There is a marshmallow building which is white when you drive past - but there are no mechanics for it yet.

Next will be the steps to link the flashing building with the ghost being at the capture screen and add other logic such as number of remaining men/traps.

There is significant slowdown when the ghosts are moving at full speed which I'll need to address. 2.5K free.

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[ChrisB]

New version today. More gameplay logic added and bugs corrected. A ghost is only present on the capture screen if the building is flashing in the map screen. Success/failure also changes the number of traps and men available and attempting to go to a capture without traps or men available produces the appropriate messages. As such you can "play" the game although there's no money accumulation and no end game states.

Known issues:

• The capture ghost can stop when over the failed man. This will change to a generic "goto" routine for movement that will be shared with other actions in the game so I will fix it then.
• The Action key does not always work on the capture screen. This is to do with my key down/key up detection to prevent repeated presses.
• Pressing B to move through stages is still works but is not recommended as the game state is not updated properly.
• If there is no ghost on the capture screen you will need to move your man to leave the screen.

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2.4 K free.

[ChrisB]

New version this week. Not much has changed in terms of gameplay.

• Changed player ghostbusters sprite to be smaller. I felt the previous one was too squashed and took up to much space on the map. Opinions welcome.

  

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• Money is added for successful ghost capture depending on how quickly you capture the ghost.
• Implemented a generic "goto" routine. This has replaced the ghost movement at the end of the screen meaning it no longer gets stuck.
• Changed the compression routine from LZSA to ZX02 (thank you Negative Charge). This has given back around 256 bytes of space.

I need to spend some time with the map algorithm for flashing new houses. Not sure what the C64 is doing here. If anyone has insights please let me know. However the "time delay" introduced by the driving also plays into this so I'm going to look at that next. 2.6K free.

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