Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uupsi!sunic!cs.umu.se!dvljrt
From: dvljrt@cs.umu.se (Joakim Rosqvist)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: 3D stuff & quick line drawing
Message-ID: <1991Apr27.175429.21010@cs.umu.se>
Date: 27 Apr 91 17:54:29 GMT
References: <20884@cbmvax.commodore.com> <1991Apr24.203219.22776@cs.umu.se> <20967@cbmvax.commodore.com>
Sender: news@cs.umu.se (News Administrator)
Organization: Dep. of Info.Proc, Umea Univ., Sweden
Lines: 37

>>BTW, i read in another article that using the blitter on short lines
>>should be a disadvantage because of the long setup-time. The breakoff
>>was given to about 150 pixels. I don't know what processor was intended
>>but I made a little test in the following environment:
>>
>>Program ran from fastmem, 68000 used, 1 bitplane 640x256 shown and
>>no interrupts enabled.
>>With the blitter i got 738000 pixels/second and 23 microsecond startup-time
>>which equals 17 extra pixels on every line. Lines between 1..25 pixels
>>all take the same time. The is beacuse the setup-time was really 58 micros
>>but for longer lines some of this could be done while the blitter was
>>drawing the previous line.
>>With the 68000 i could get about 150000 pixels/sec and 24 micros 'setup'
>>(I clocked a MAC SE/30 using quickdraw to 110000 pix/sec  giggle..)
>>This means that the breakoff(=the number of pixels where using the blitter
>>or the 68000 would take the same time) would be at 5 pixels.
>>
>
>You don't say if the lines are arbitrary direction. Sure, for short horizontal
>lines, you would be better off using the CPU, but I doubt that's the case for
>lines of any angle of more than a few pixels.
>
Of course, I gave you the figures to show that there really is no point
in using the 68000. The value 150000 corresponds to an 22-degree line
Lines that are 0 or 90 degress will be the fastest and 45 deg the slowest
so i used 22 as an in-between. 
And.. the 68000 will always win over the blitter for horisontal lines.
This is because it can do a:

label:  move.l d7,(a0)+
	dbra   d0,label

Where a0 is a pointer in the bitplane and d7 is $FFFFFFFF.
The poor blitter would read a word, set a bit, write it back then read
it again.. 16 times without knowing it's the same word :-(

/$DR.HEX$