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Old 08 December 2015, 21:44   #5
Mrs Beanbag
Glastonbridge Software
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Join Date: Jan 2012
Location: Edinburgh/Scotland
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i think the question is about why the scrolling is not smooth, rather than why there is not parallax. It seems the assumption is that parallax would slow it down, so it would be an excuse if it were present...

Well there are (at least) two ways to achieve parallax on the Amiga, the most obvious way is "dual playfield mode" which allows you to have two screens superimposed in hardware, with one showing through the gaps in the other. There is not much performance hit, because it is a hardware mode, but you only get to use 3 bitplanes (i.e. 8 colours) per screen, so it really limits your graphics (on AGA this is better because you get two 16-colour playfields, so a lot of AGA versions of games could "easily" put a parallax layer in since the main graphics were already 16 colours anyway). There are some games that make it work, Kid Chaos and Soccer Kid are two that spring to mind, but Bitmap Brothers have their graphical style which maybe wouldn't translate very well.

Another way to achieve it is to use the blitter, to copy the background layer behind the foreground layer on every frame. You can use any colours you like with this method of course, but there is a speed penalty of actually having to copy a screen-sized graphic every frame. It's do-able with how bad the scrolling is on Gods (it appears to scroll about every 3 vbls) but on the whole there's not many gaps in the foreground for a background to show through anyway. More likely they just didn't want to do any extra work for the Amiga version over the ST version that they didn't have to.

I believe Agony uses a combination of the two above approaches to achieve 3 parallax layers.

another way to get parallax effects is to use sprites to do it, since they can be placed above, below or between the playfields. Jim Power uses sprites to achieve a third (stationary) parallax layer at the back. But you have to re-use sprites across the screen so you need a very heavy copper list, and usually a repetitive pattern.
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