Quote:
Originally Posted by coder76
"BOBs per 320x256 PAL frame:
OCS 4 BPL: 46704/2304*0,9=about 18 bobs
OCS 5 BPL: 41328/2880*0,9=about 12 bobs
AGA 8 BPL: 55920/4608*0,95=about 11 bobs
AGA 16+16 Dual Playfield mode: 55920/2304*0,95=about 23 bobs"
Interesting figures here, and really shows how inefficient the blitter is. If we take OCS 4 bitplanes and 32x32 size, the effective bandwidth for bobs is 32*4*4*18*50=460,80 kB/sec. This can be compared to blitter copy speed of 3,3 MB/sec.
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Well, it's not really inefficient per se... The issues the Blitter has here also exist for CPU based drawing methods (but less so as the Blitter has less overhead in drawing than the 68000/68020). It's rather the reverse: Sprites are simply vastly more efficient than the Blitter/CPU
The Blitter (nor the CPU, Copper or Sprites for that matter) simply can't access the cycles that bitplane DMA use so you have to subtract those from any bandwidth figure you get. Furthermore, blitting a bob is also a two step process (cookie-cut draw & restore), which drops "Bob bandwidth" quite severely.
But yeah, Sprites are massively more efficient. Use them
Edit: I just noted the numbers you use might be a slight underestimation (well, IMHO anyway), I'd say the number should be 32*6*4*18*50=675KB/sec. Reason for this is that the Blitter (or any word based algorithm really) needs some extra "space" for shifting the data, which adds an additional word per line to draw. Then again, I suppose you could argue that this shifting space isn't really part of the "bob"... Swings and roundabouts...