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多边形另一个世界：世嘉创世纪

法比恩•桑格拉德（Fabien Sanglard）系列第五条的翻译，这次是关于世嘉创世纪的另一个世界港口。


世嘉于1987年推出其Master System之后，即刻开始了MegaDrive / Genesis的开发。当时，世嘉的目标是创造出超越NEC的PC引擎和任天堂的Famicom的产品。




系列文章


  1. 多边形另一个世界。
  2. 多边形另一个世界：Amiga 500。
  3. 多边形另一个世界：Atari ST。
  4. Another World: IBM PC.
  5. Another World: Sega Genesis.



16- . , 29 1988 , , 400 000 . NES , MegaDrive .



( 1989 .) ( 1990 .) [1]. 1990 , Sega America. , , («Genesis does what Nintendon't») Altered Beast Sonic the Hedgehog Genesis -.



Nintendo SNES NEC TurboGrafx-16, Sega 1992 65% 16- Nintendo 1990 1994 . 39,7 [2].





, Genesis Motorola 68000 (7,61 ), 8 , 64 , 64 , ASIC (13 ) Z-80 (3,58 ) 8 TI 76489 YM 2612.






, , VDP (Video Display Processor). VRAM CRAM, .


, 68000 VRAM, «» VDP , RAM. DMA , RAM VRAM. VDP VRAM /, .


68000 DMA , Z-80 , .


DMA BLANK , 68000. , 68000 .


— Genesis Developer Manual

Atari ST 3 , 9 .






(VDP)


VDP ASIC . , . [3], Scroll B, Scroll A, Windows Sprites.



Scroll A Scroll B . , . Scroll A «Window», HUD .


4- (, ). 0 . 15 [4]. 128 , CRAM.


VDP , , . () , ( 0). , Z- Scroll B, , Sprite, . VDP , .




8x8. 32 , 8 .



VRAM (64 ):
==========================

WORD | WORD | WORD | WORD |
-----------------------------------------------------
BYTE | BYTE | BYTE | BYTE | BYTE | BYTE | BYTE | BYTE
-----------------------------------------------------
0 0 F F F F 0 0 0 F 0 0 0 0 F 0
F 0 F 0 F 0 0 F F 0 F 0 F 0 0 F
F 0 0 0 0 F 0 F F 0 F F F 0 0 F
0 F 0 0 0 0 F 0 0 0 F F F F 0 0

(8 8 ):
=============================

0 0 F F F F 0 0
0 F 0 0 0 0 F 0
F 0 F 0 F 0 0 F
F 0 F 0 F 0 0 F
F 0 0 0 0 F 0 F
F 0 F F F 0 0 F
0 F 0 0 0 0 F 0
0 0 F F F X 0 0

« »[5].


80 . , , 88 3232. ( 512x512, ) « »[6].


: «H32» 32x28 (256x224 ) «H40» 40x28 (320x224 ).



NTSC vs PAL


. PAL 576 , NTSC 486 . Genesis , PAL 30 ( , NTSC 28). . , .





— MegaDrive, Sonic The Hedgehog, 17% ( ). , VBLANK, , 16 . PAL 50 , NTSC 60 , VBLANK 20 , 16.



Another World Genesis


Genesis — , , Delphine Software. Interplay Genesis, Macintosh, Super Nintendo Apple IIGS.


Sega , . Genesis 68000, Atari ST .


Interplay , TV [7]. Out Of This World. , Out Of This World 1991 [8], .


Interplay , , .





, , GenS Exodus, .




Genesis[9] — , DMA. , , VDP , , Another World .


VDP DMA FILL[10] , Amiga Blitter. DMA COPY[11] VM COPY. , .


-, VRAM. 320x200 VRAM — 64 . , , , .


-, DMA FILL 16- , , , VRAM VDP, .


, , DMA FILL. Another World , (4 ) 28 . DMA FILL , , .


VDP #17[12] Exodus, , DMA COPY DMA FILL .


Another World Genesis



, VDP, VRAM, Another World 68000 , , Atari ST.


, BKGD «» . 68000 .


, DMA VRAM. VBLANK «» VRAM .


, Scroll A, Gens. Scroll A , .


Atari ST , -, COPY, movem. (5%?).






VAM VRAM , , .


pixel perfect H40 320x224 . 320200, .


320x200 320 * 300/2 = 32 000 . VDP DMA[13], , NTSC 32000/11556 = 2,7 , PAL 32000/21654 = 1,4 .



DMA, /:
===============================

On VBLANK On Active Display Total
--------------------------------------------------------------------------
60 Hz 256 x 224 6118 3584 9702
320 x 224 7524 4032 11556
50 Hz 256 x 224 14329 3584 17913
320 x 224 17622 4032 21654
256 x 240 11753 3840 15593
320 x 240 14454 4320 18774

: , PAL NTSC, VRAM. - PAL MegaDrive NTSC Genesis.


RAM VRAM, , 12-15 NTSC, .



Framerate for # missed VSYNCs:
==============================

Missed VSYNCs : 0 1 2 3 4 5 6 7
-------------------------------------------------------
NTSC Framerate : 60 30 20 15 12 10 8 7
PAL Framerate : 50 25 16 12 10 8 7 6


, VDP «H32» 3228. . , , 1,3.


28x22 , 224x176 224 * 176/2 = 19,712 .


, , RAM VRAM. NTSC 19,712 / 9702 = 2 . //, 15-12 , , , [14].


PAL 19712/17913 = 1,1 . , , 2 vsync , NTSC, 16-12fps.





, . ( ). , .




- — VDP . , . , , 15. Another World 16. .


B 0x01. 0 A B 0x01. . B A, , 0x0, 0x1 B.


, . Exodus , , 0. , , BACKGROUND COLOR (, , ) .





, , . VDP, MegaDrive, , RAM/VRAM, , , .


, - , , , , , .


, , , . NTSC , PAL «» .


? . StarFox SNES / , . , Out of This World/Another world Genesis/MegaDrive.





  1. Wikipedia: Sega Genesis, .
  2. Mega Drive.
  3. Genesis Software Manual: VDP 315-5313.
  4. , HBLANK BACKGROUND REGISTER, .
  5. VDP, .
  6. VDP,
  7. (, 1964).
  8. (, 1981).
  9. Genesis Software Manual..
  10. VDP DMA FILL.
  11. VDP DMA COPY.
  12. VDP Registers 0x17.
  13. segaretro.org, MegaDrive DMA Bandwidth.
  14. Out of This World on US Model 2 Sega Genesis through S-Video.

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