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Old 20 January 2019, 18:13   #1
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16c single playfield vs dual playfield for bobs n sprites

If you want to display lots of animated sprites and bobs what is best?

Dual playfield or single playfield with 16 colours.

ocs hardware, everything else equal.
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Old 20 January 2019, 18:24   #2
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This may surprise you, but it doesn't really matter (if both assume say a 320x256 screen).

The number of sprites you can show is equal regardless of screenmode* and the extra DMA cycles used by Dual Playfield mode (in 6 bitplane mode) is more or less cancelled out by the lower number of DMA cycles used by blitting Bobs in fewer bitplanes (i.e. 3 vs 4).

If you like I could post the calculation results to show this is true, but for now I'll leave it here.

Now, do note that while the above is true, Dual Playfield mode's extra cycle use does mean there is less CPU time available and this may impact the ability to keep all objects moving & animating. However, I don't really feel this is a problem simply by looking at Amiga games that already exist - competent Dual Playfield don't seem to be any less busy than competent 16 colour games.

*) A caveat here is that reloading sprites with the copper takes more cycles, so fewer sprites can horizontally be reloaded. However, in practice horizontal reloading of sprites is almost never done for moving objects, usually this is limited to a background layer.

Edit: I would like to add that I am assuming you want both layers to contains graphics other than just Bobs, if you use Dual Playfield mode and use one layer for Bobs and the other as the background layer, Dual Playfield is in fact the faster option.

Last edited by roondar; 20 January 2019 at 22:53. Reason: Clarified what kind of Dual Playfield I was talking about
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