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Old 13 October 2017, 08:50   #1
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256 Colours, Chunky Vs Planar, what was better?

I know the Amiga used Planar graphics, but for 256 colours, would chunky be the best format?

Planar, 40 bytes * 200 lines * 8 bitplanes = 64,000 bytes
Chunky, 1 bytes (from 00 - 256) * 320 pixels a line * 200 lines = 64,000 bytes.

It just seems like a lot of effort on a planar system having to go through every one of those 8 bitmaps to set the bit for a colour change? Trying to shift some sprites across seems like it would be a nightmare on a planar system. Is there any advantage of a 256 colour planar system?

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Old 13 October 2017, 09:54   #2
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One advantage of an 8 bitplane planar system is you can have 2 independent 4 bitplane
playfields, which would be good for parallax scrolling and other similar effects.
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Old 13 October 2017, 10:11   #3
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Burst fetches and page fetches benefit chunky modes more. Likewise, narrow blits like the ones used in texture mapping favor chunky modes.

Planar modes are favored by a simpler GPU design and bitfield partitioning strategies. Among them are the ability to shade spread palettes algorithmically and the famous dual playfield mode, as mentioned.

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Old 13 October 2017, 13:24   #4
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Planar made sense initially because graphics performance was relatively low and planar made it easy to scale memory, DMA and performance. It was a good trade off of flexibility and a slightly awkward format.

When AGA was being designed they just wanted something quick, so they simply increased the number of available bitplanes and added 32 bit capability to support them. Even later the Akkiko chip was thrown in, but it was all just because unsufficient resources went to developing AAA with proper chunky modes.
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Old 14 October 2017, 14:23   #5
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Both chunky and planar modes have their own advantages. But there exists chunky to planar routines (c2p's), which converts a chunky screen held in fast ram to chip ram planar format. On a 68040/68060 its copyspeed, so this conversion does not slow down copy speed to chip ram. With Doom, you really see that planar format does not slow down faster Amigas. A 68030/50 MHz even outperforms a 386/40 MHz running Doom in benchmarks by a frame or two, despite doing the c2p. Also, a 68040 outperforms a 486 PC running Doom at same clockspeed. The chip ram access speed is more of a bottleneck on the Amigas, rather than the planar format.
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