mo@seismo.CSS.GOV (Mike O'Dell) (03/10/87)
Note that I didn't say there weren't fast bit blitters if you just look at some spec sheet about how fast the hardware can run in some cases the hardware does well. The point is that THEY USUALLY DON'T DO ALL THE CASES!! Making up for the boundary conditions in software is often slower than just doing it with the CPU in the first place. And as for the speed of a 68K, my Macintosh can paint rings around my SUN 3/160. Maybe it is the cruft getting to the pixrects, but the end result is that my Macintosh paints windows much faster per unit area. And having seen an SE do it, it does it faster than our SUN 3/260. -Mike
dillon@CORY.BERKELEY.EDU.UUCP (03/11/87)
>Note that I didn't say there weren't fast bit >blitters if you just look at some spec sheet about >how fast the hardware can run in some cases >the hardware does well. The point is that >THEY USUALLY DON'T DO ALL THE CASES!! >Making up for the boundary conditions >in software is often slower than just doing it >with the CPU in the first place. > > -Mike No, but they can get pretty close. Citing the Amiga blitter as an example: It can do any logic operation on it's 3 sources and 1 destination. That's 256 logic operations! (I'm not starting a war, just giving you an example of a real-life blitter). Certainly doing extremely simple operations can be done relatively fast by the 68000/68010 (about 3 times slower than a blitter running at the same speed), but when you get into more complex equations, for instance: ((C&A)|D)->D (Take bitmaps A through template C and OR onto the destination bitmap) The problem suddenly becomes non-trivial... especially when three of the four bitmaps are on different bit boundries. (in the example above, D is used both as a source and as a destination). Were talking about 10x slower at a minimum. Even a 68020 with it's cache would have a time of it (perhaps only 3x slower). A good example is the LIFE program on the Amiga using the blitter and the LIFE program on the atari using the processor. Of course, you cannot do a life-entity calculation in one blit... it takes the Amiga about 12 I believe. So the Amiga is actually doing 20*12 = 240 complete blitter passes over the screen per second. Even though it takes the blitter 12 passes per life entity, it is still 3 times faster than the Atari version written in extremely optimized assembly. There can be no question that having one or more blitters gives a huge advantage when manipulating displays. -Matt
berger@datacube.UUCP (03/11/87)
Ok, I'll trade my Mac for your sun 3/260 :=)
Bob Berger
Datacube Inc. Systems / Software Group 4 Dearborn Rd. Peabody, Ma 01960
VOICE: 617-535-6644; FAX: (617) 535-5643; TWX: (710) 347-0125
UUCP: ihnp4!datacube!berger
{seismo,cbosgd,cuae2,mit-eddie}!mirror!datacube!bergerkevin@violet.berkeley.edu.UUCP (03/11/87)
This (now boring) thread began with a very simply question re: the Macintosh II's blit (or non-blit) capabilities. Obviously this has deteriorated greatly and is possibly more appropriate in comp.graphics. The Macintosh II motherboard has _no_ graphics at all. PERIOD. Apple's announced video adpater does not blit. So what. Before we know it every add-on vendor and their relatives will offer a graphics controller with and with-out graphics co-processors. Take your choice. Unfortunately these boards will probably be available LONG before you or I can get our little hands on the new Mac. (Remember 1984 ....) Kevin (waiting in line for the Mac II)
radford@calgary.UUCP (03/13/87)
In article <8703110056.AA23131@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU.UUCP writes: > There can be no question that having one or more blitters gives a huge > advantage when manipulating displays. Your're right. Certain operations of moderate complexity - not too simple like a memory copy, and not too complex, beyond what it was designed for - can be done much more rapidly by a blitter than by a processor like the 68020. The real question is whether the blitter is worth its cost. Machines like the Mac and the Amiga don't run at the limits of speed for the 68000 family. Would you rather have a blitter, or have the processor run 30% faster for all operations? The cost may be comparable. And don't say you'd like both. :-) Radford Neal
ali@rocky.UUCP (03/14/87)
In article <828@vaxb.calgary.UUCP> radford@calgary.UUCP (Radford Neal) writes: >The real question is whether the blitter is worth its cost. Machines like >the Mac and the Amiga don't run at the limits of speed for the 68000 family. >Would you rather have a blitter, or have the processor run 30% faster for >all operations? The cost may be comparable. That's true only if you're not multitasking. In a multitasking OS the CPU might get a lot of use, even if it is faster. The blitter will assure that the CPU will not be interrupted for various simple but necessary tasks (such a windowing, sizing, menu operations, etc...). Of course, if you get a Mac II just to run Mac software than the 68020 is fast enough such that you won't need a blitter. But, a blitter will be necessary when running multiple Mac applications under A/UX (if such a thing will ever be possible). Ali
dillon@CORY.BERKELEY.EDU.UUCP (03/14/87)
> >> There can be no question that having one or more blitters gives a huge >> advantage when manipulating displays. > >Your're right. Certain operations of moderate complexity - not too simple >like a memory copy, and not too complex, beyond what it was designed for - >can be done much more rapidly by a blitter than by a processor like the >68020. > Those 'Certain operations' you so glibly discard with a wave of your Overview comprise about 60% of all video operations. If you include blitter aided text display, the figure is around 95%. Although the 'processor offloading' aspect doesn't apply as much to the Mac due to it's lack of multi-tasking, you still get a pretty hefty gain in speed. And when your talking about 8 bit planes for the Mac II, and super-large windows, a blitter makes all the difference in the world. >The real question is whether the blitter is worth its cost. Machines like >the Mac and the Amiga don't run at the limits of speed for the 68000 family. >Would you rather have a blitter, or have the processor run 30% faster for >all operations? The cost may be comparable. > >And don't say you'd like both. :-) > > Radford Neal This may be true in some systems, but as far as the Amiga goes, both its processor and its blitter can run at full speed simultaniously, and video refresh doesn't slow down the processor until you get beyond 4 planes 320x(200/400) or 2 planes 640x(200/400). As for the Mac II, since the video cards have their own video memory, it would be very easy for a third party developer to stick on a blitter with relatively little interference with the processor. The *real* question is: "Would QuickDraw Support hardware aided operations???" -Matt
shap@sfsup.UUCP (03/18/87)
In article <188@rocky.STANFORD.EDU>, ali@rocky.STANFORD.EDU (Ali Ozer) writes: > In article <828@vaxb.calgary.UUCP> radford@calgary.UUCP (Radford Neal) writes: > >The real question is whether the blitter is worth its cost. > > That's true only if you're not multitasking... > ... But, a blitter will be > necessary when running multiple Mac applications under A/UX (if such a thing > will ever be possible). > > Ali My preference is to put certain carefully chosen graphics operations in hardware. It is worth pointing out, however, that so long as the main processor doesn't need to worry about actually doing the screen output (i.e. some dedicated hardware takes on the job of pumping the dots), one does not *need* a blitter. Ever. In lower display densities one doesn't even need dedicated dot-pumper. A blitter is desirable for many applications. Some will view it as a necessity. But it is a matter of cost, and many people will deem the cost unjustifiable. I want a blitter. I don't want everyone else to have to buy my choice. Please, instead of talking religion (e.g. "This machine MUST have a blitter), can we talk about the merits/demerits of one choice or the other? I think that Apple's decision not to put a blitter on the main board was sound. It means that graphics hardware vendors can build there hardware according to their needs, and different kinds of hardware have different needs. Jonathan S. Shapiro