Turrican 3 first level copper bars, how were they done?

[lionagony]

Was just wondering how the copper bars were done which can be seen around 3:22 here [ Show youtube player ] The reason I ask is because they appear to have almost 2 layers to them unlike most other copper bars that just look like one layer. Are the thicker bars somehow drawn in the foreground and the thinner ones are the actual copper bars?

Another question, was just re-reading the Turrican 3 AGA thread by Muzza and he said "Some levels go down to four colours in the foreground (almost black and white) to try and preserve the parallax." I just wondered what technical benefit would going down to 4 colors have instead of sticking to the usual 7 or 8 colors of dual playfield? I always just assumed that the speed would be the same whether you used all the available colors or not in that mode. Thanks for any insight.

[kamelito]

Check the source code.

[jotd]

you can simulate layers by (at each frame) first setting the colors for 1 layer in the copperlist, then set the colors for the second layer, overwriting some color lines. Each color line is independent. They always set the color at start of display window start & end it at the end of display window anyway else on OCS since there's no border blanking you'd get color bleed in the border, which is not cool.

I would do that that way. Checking the source code is always possible as it's available, even if it's easier said than done.

[lionagony]

Originally Posted by jotd

you can simulate layers by (at each frame) first setting the colors for 1 layer in the copperlist, then set the colors for the second layer, overwriting some color lines. Each color line is independent. They always set the color at start of display window start & end it at the end of display window anyway else on OCS since there's no border blanking you'd get color bleed in the border, which is not cool.

I would do that that way. Checking the source code is always possible as it's available, even if it's easier said than done.

Thanks, very interesting. I'm not really a coder (just using Scorpion Engine to make my game) so maybe I should have posted this in Retrogaming General instead. I just am fascinated by the Amiga's technical abilities and love to learn more about the basic principles, your answer helps out there so thanks again.

[lionagony]

Originally Posted by jotd

you can simulate layers by (at each frame) first setting the colors for 1 layer in the copperlist, then set the colors for the second layer, overwriting some color lines. Each color line is independent. They always set the color at start of display window start & end it at the end of display window anyway else on OCS since there's no border blanking you'd get color bleed in the border, which is not cool.

Was just thinking what would the theoretical maximum number of layers that would be possible with this technique? Could maybe lead to some interesting effects, I've never seen it in another game besides Turrican 3 that I can think of.

[koobo]

Somewhat related, there's a recent intro from Revision2024 with a lot of raster bars:
Automated Raster Machine [ Amiga 64k Intro ] / Tristar & Red Sector Inc.
[ Show youtube player ]

[Rob68K]

Originally Posted by lionagony

Was just wondering how the copper bars were done which can be seen around 3:22 here

Just think of the copper list no differently to a bitmap.

You could draw these bars onto the screen using just regular 'graphics', right?

Same way, you just redraw the colours you want into a copper list.

Copper bars are not entities which only exist in one dimension which need to respect each other's space.

If a red bar moves up towards a blue bar, it's not going to panic any more so than an explosion sprite is any more complicated to draw if it's on top of an NPC rather than just the background.

Now how's that for an over-explanation?

[jotd]

except that changing color 0 only takes a couple of writes in chip memory.

The copperlist is already filled with say 200 times:

- wait for 1 line, until X=start of display
- set color0 to <fill the blank>
- wait for end of line
- set color0 to 0
- repeat...

To change a color on a whole line you just have to write 2 bytes in <fill the blank>, instead of 160 bytes to write a line of 40*8 pixels on 4 planes. Bargain!

[Muzza]

Originally Posted by lionagony

"Some levels go down to four colours in the foreground (almost black and white) to try and preserve the parallax."

I think I was mistaken about that. It is 8 colours. Just mostly greys and it looked like 4 at first.

[lionagony]

Originally Posted by Muzza

I think I was mistaken about that. It is 8 colours. Just mostly greys and it looked like 4 at first.

OK, yeah I always thought the greys was an odd choice. They kept the background parallax almost exactly the same as the Mega Drive but went for monochromatic for the foreground and bobs including the powerups. I think one red or one green at least would have made things look better. Also I guess they weren't aware of the technique that Chuck Rock 2 and others used where you could make some bobs from the back playfield colors.