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Reply-To: "Geraldo Sazias"
From: "Geraldo Sazias"
References: <3D8EC516.email@example.com> <firstname.lastname@example.org> <email@example.com>
Subject: Re: Simple Graphic Processors?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Wed, 25 Sep 2002 10:37:43 GMT
NNTP-Posting-Date: Wed, 25 Sep 2002 12:37:43 MEST
"Lewin A.R.W. Edwards" wrote in message
> "Geraldo Sazias" wrote in message
> > > The ability to detect the end of a frame is essential, but hardware
> > > blit assistance is absolutely not.
> > Are you using a graphical LCD with a 'dumb' controller (such as
> Yes. In one case, a Winbond W9971 (it has some simple hardware
> assistance, but I'm not using any of it). In another case, a SED1355.
> In a third case, I am using a dumb framebuffer integrated into the
> Geode chipset. In a fourth case, I am using the dumb single-page,
> no-hardware-assist LCD controller in the Cirrus CL-EP7312.
> > So the framebuffer is simply located in physical memory and you transfer
> > graphics by way of writing them to the LCD bytewise? I think that's
> > too slow for my application as I'm trying to design a portable gaming
> > device.
> It's adequate for full-screen MPEG-1 video playback and animated
> "screensaver" type code that closely resembles a game, so it's more
> than adequate for most 2D gaming applications. I think you should
> study the problem a little more closely, in particular examine the
> techniques used for 2D gaming developed on blitterless 16-bit
> platforms like the Atari ST, and also some 8-bit platforms such as the
> Commodore 64.
> Also look at the design tradeoffs that have been made in similar
> consumer appliances on the market. For sprite-based 2D gaming, the
> normal hardware assistance that is provided is an on-chip tile-based
> character generator (actually usually more than one, for multiple
> layers of parallax-scrollable playfield), and hardware sprite
> generators for characters and bullets. Hardware blitters are not
> normally found in this application. Using tiles and sprites you can
> obtain a satisfying gameplay experience, including audio, with a
> single 8-bit main microcontroller (perfect example: Gameboy and
> Gameboy Color). This minimizes overall system cost and power
> consumption. In such a system, the bulk graphics data is never
> normally in the processor's address space. The CPU only manipulates a
> relatively small matrix of color attribute bytes and tile bytes, and a
> couple of smooth-scroll registers. The tile and attribute RAM is DMA'd
> by the tile and sprite hardware, which uses the information as
> pointers into graphics ROM.
> If you are using a 32-bit core like ARM, the tile and sprite hardware
> is not necessary to achieve an enjoyable gaming experience. On a 74MHz
> ARM7 core with a 320x240x8bpp display* it is perfectly possible to
> have an entire playfield generated offscreen (double-buffering)
> including a large number of sprites and at least two or three layers
> of tiled playfield. In such a system you're effectively emulating tile
> and sprite hardware using software. I wrote a lot of such code (an
> "emulator" for a nonexistent piece of coin-op arcade hardware) on the
> Macintosh. Again, simple dumb linear framebuffer code with no hardware
> page-flipping or blitting of any kind. You generate the frame into an
> offscreen buffer, wait for end of physical frame display, then
> (software-)blit the new frame onto the live framebuffer.
> * - This becomes a pain in the ass with certain display modes, however
> - 12bpp in particular.
> For 3D gaming, you are really out of the realm of 8-bit and preferably
> hardware assistance should be available.
Yes, I think you're right. Quick calculation: 320 x 240 x 2 (i.e. 16 bit
color) = 153.600 bytes per frame x 25 fps = 3.840.000 bytes / sec, which is
about 4Mhz computing power of 74Mhz power available for an ARM or about 6%.
OTOH the SW still has to render the frame by blitting in memory to a frame
buffer, which takes up another couple of percent (the 'blitting' can be done
with 32-bits so it's probably going to be less than 5% overhead). That still
leaves 90% of the processor power for game-logic and the like.
Thanks for the advice, I'll think it over.
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