NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/sys/amiga/programmer/3242

Internet Message Format | 1996-08-05 | 4.9 KB

Path: informatik.tu-muenchen.de!fischerj
From: [e-mail] (Juergen "Rally" Fischer)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: doubling pixels horizontally
Date: 9 Feb 1996 13:47:31 GMT
Organization: Technische Universitaet Muenchen, Germany
Distribution: world
Message-ID: <4ffj9j$[e-mail]>
References: <4f4ibc$[e-mail]> <[e-mail]>  <[e-mail]> <4faoe1$[e-mail]> <[e-mail]>
NNTP-Posting-Host: hphalle5.informatik.tu-muenchen.de
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In article <[e-mail]>, [e-mail] (Hans Henrik Happe) writes:
|> Organization: CyberCity of Denmark
|> Lines: 83
|> Message-ID: <[e-mail]>
|> References: <4f4ibc$[e-mail]> <[e-mail]>
|>     <[e-mail]> <4faoe1$[e-mail]>
|> NNTP-Posting-Host: 194.16.56.145
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|>
|> Juergen "Rally" Fischer ( [e-mail] ) wrote:
|> > In article <[e-mail]>, [e-mail]
|> > (Hans Henrik Happe) writes:
|> >|> Organization: CyberCity of Denmark
|> >|> Lines: 33
|> >|> Message-ID: <[e-mail]>
|> >|> References: <4f4ibc$[e-mail]>
|> >|> <[e-mail]> NNTP-Posting-Host: 194.16.56.105
|> >|> X-Newsreader: THOR 2.22 (Amiga;TCP/IP) *UNREGISTERED*
|> >|>
|> >|>
|> >|> Patrick Hanevold ( [e-mail] ) wrote:
|> >|> >>I wonder how to double pixels horizontally without writing
|> >|> >>them twice! I've seen this trick in several demos and I
|> >|> >>believe that it is just a little trick with the hardware.
|> >|> >>I also wonder about another thing:
|> >|> >>you may have noticed that there is a "sprite mode" where
|> >|> >>the sprite switches from Hires back to Lores and displays
|> >|> >>only every second column of pixels! I wonder if this is
|> >|> >>possible/will happen  for bitmaps too.
|> >|>
|> >|> > It's in the chunky to planar convertion.
|> >|>
|> >|> You can also render only every 2nd pixels, mask out those you don't want
|> >|> with sprites, and then:
|> >|>
|> >|> loop
|> >|>     1st frame: show pixel 02468... mask out 13579...
|> >|>     2nd frame: show pixel 13579... mask out 02468...
|> >|>     jump loop
|> >|>
|> >|> In the 2nd frame you shift (scroll) the bitplanes 1 to the right.
|> >|> This looks allmost as the real double pixels (Gives very little flicker)
|> >|> and you only have to write half as much to the chip mem.
|>
|> > not really. to change 100 pixels, you got to write 100 words.
|> > only fx running 50Hz might work with the trick of writing
|> > only 50 pix each frame, but then gfx maybe doesn't look
|> > more like 50pix.
|>
|> A bitmap for this screen would look like this:
|>
|> ChipMem: 0101010101...  ; the '0' representing bitplane 0, '1' bitplane 1
|>          ^^^^^^^^^^
|> Pixel:   0011223344
|>
|> will be combined this way:
|>
|> 1st frame:
|>
|> blp0pt = ChipMem; scroll 1 to the right | 010101010...
|> blp1pt = ChipMem                        |010101010...
|> sprite mask:                            | sbsbsbsbs  ; s = see throuth, b = black
|>
|> 2nd frame:
|>
|> blp0pt = ChipMem, scroll 2 to the right |  010101010...
|> blp1pt = ChipMem  scroll 1 to the right | 010101010...
|> sprite mask:                            |  sbsbsbsbs  ; s = see throuth, b = black
|>
|> This is actually just like a 2pass scrabeled or 3pass nonscrab. blitterscreen,
|> with spritemasks.

huh, you're explaining blitterscreen to ME ? =:D

mhm sorry I don't know how I got the idea you did a coperscreen :)
You said "render every 2n pixel". well, cpu renders normal linear memory.

I agree, with the lace method you get the normal blocky 2x2 lock,
there you are, you wanted it like that ;) I still prefer ghost-look
for most cases, it just looks more like hires.

|>
|> >|>
|> >|> This effect can be done using only the copper.
|>
|> > aah, you mean interlaced copperscreen to get more resolution.
|> > well. gives 200x256 1x2.
|>
|> Not copperscreens. You use the copper to change sprite-pos, shifts and double vert. lines
|> from frame to frame. Call it double buffered copper if you like.

argh I was misdirected.

|>
|> > IMHO copperscreens are only usefull for demos.
|> > use 3pass-c2p ("blitterscreen") or 4pass-c2p for games.
|>
|>       2pass-c2p 2x2 scrab. 3pass-c2p 2x2 nonscrab. is what
|>       my blitterscreen can do, the same goes for 2x1.
|>
yes, same specs for 2x1. I prefer the 3pass version, 2 pass is only
useful for very special renderers.

|>
|> Hans Henrik Happe
|>  Goat / Sumpen
|>
------------------------------------------------------------------------
   [e-mail] (Juergen "Rally" Fischer)   =:)