Difference between revisions of "VDP1 (Saturn)"

From Sega Retro

Line 57: Line 57:
 
** Maximum sprites per frame: 16,383 (virtually unlimited),{{fileref|NextGeneration US 24.pdf|page=64}} 13,106 (Gouraud shading), 5461–8191 (shadows)
 
** Maximum sprites per frame: 16,383 (virtually unlimited),{{fileref|NextGeneration US 24.pdf|page=64}} 13,106 (Gouraud shading), 5461–8191 (shadows)
 
** Maximum polygons per frame: 16,384 (flat shading), 16,383 (texture mapping), 13,107 (Gouraud shading), 13,106 (texture mapping, Gouraud shading), 8192 (shadows), 8191 (texture mapping, shadows), 7281 (texture mapping, shadows, Gouraud shading)
 
** Maximum polygons per frame: 16,384 (flat shading), 16,383 (texture mapping), 13,107 (Gouraud shading), 13,106 (texture mapping, Gouraud shading), 8192 (shadows), 8191 (texture mapping, shadows), 7281 (texture mapping, shadows, Gouraud shading)
* Framebuffer [[fillrate]]: 28.63636 [[Pixel|MPixels/s]] 16bpp (1 cycle/[[pixel]]),{{fileref|ST-013-R3-061694.pdf|page=52}}{{fileref|ST-013-R3-061694.pdf|page=35}}{{fileref|ST-013-R3-061694.pdf|page=64}} 35.6465 MPixels/s 8bpp (28.63636 MPixels/s draw, 14.418 MPixels/s erase/write){{fileref|ST-013-R3-061694.pdf|page=65}}{{fileref|ST-013-R3-061694.pdf|page=61}}
+
* Framebuffer [[fillrate]]: 28.63636 [[Pixel|MPixels/s]] (16bpp),{{ref|1 cycle per [[pixel]]{{fileref|ST-013-R3-061694.pdf|page=52}}{{fileref|ST-013-R3-061694.pdf|page=35}}{{fileref|ST-013-R3-061694.pdf|page=64}}|group=fn}} 35.6465 MPixels/s (8bpp){{ref|28.63636 MPixels/s draw, 14.418 MPixels/s erase/write{{fileref|ST-013-R3-061694.pdf|page=65}}{{fileref|ST-013-R3-061694.pdf|page=61}}|group=fn}}
** Shadows/Translucency: 4.772733 MPixels/s (6 cycles/pixel){{fileref|ST-013-R3-061694.pdf|page=110}}
+
** Shadows/Translucency: 4.772733 MPixels/s to 28.63636 [[Pixel|MPixels/s]]{{ref|Takes six times longer when using VDP1's RGB mode.{{fileref|ST-013-R3-061694.pdf|page=110}} When using VDP2 palette mode, the VDP1 draws shadowed/translucent objects at full speed.|group=fn}}
 
* Texture mapping fillrate: 28.53144 MTexels/s (504×255 textures), 18.205888 MTexels/s (8×8 textures){{ref|85.90908 million bus cycles/sec, 222 textured 504×255 polygons/sec (386,905 cycles per polygon), 284,467 textured 8×8 polygons/sec (302 cycles per polygon){{fileref|TUTORIAL.pdf|page=8}}|group=fn}}
 
* Texture mapping fillrate: 28.53144 MTexels/s (504×255 textures), 18.205888 MTexels/s (8×8 textures){{ref|85.90908 million bus cycles/sec, 222 textured 504×255 polygons/sec (386,905 cycles per polygon), 284,467 textured 8×8 polygons/sec (302 cycles per polygon){{fileref|TUTORIAL.pdf|page=8}}|group=fn}}
 
** Gouraud shading: 28.40292 MTexels/s (504×255 textures), 10.373888 MTexels/s (8×8 textures){{ref|85.90908 million bus cycles/sec, 221 textured 504×255 polygons/sec (387,137 cycles per polygon), 162,092 textured 8×8 polygons/sec (530 cycles per polygon){{fileref|TUTORIAL.pdf|page=8}}{{intref|Saturn VDP1 hardware notes (2003-05-17)}}|group=fn}}
 
** Gouraud shading: 28.40292 MTexels/s (504×255 textures), 10.373888 MTexels/s (8×8 textures){{ref|85.90908 million bus cycles/sec, 221 textured 504×255 polygons/sec (387,137 cycles per polygon), 162,092 textured 8×8 polygons/sec (530 cycles per polygon){{fileref|TUTORIAL.pdf|page=8}}{{intref|Saturn VDP1 hardware notes (2003-05-17)}}|group=fn}}

Revision as of 17:10, 4 December 2016

315-5688 VDP1 01.jpg

Video Display Processor 1 (VDP1) is one of two graphics processing units housed within the Sega Saturn console. It is a custom integrated circuit used only in Saturn hardware, and the Saturn-derived Sega Titan Video arcade hardware.

VDP1 is typically responsible for rendering all "foreground" graphics, such as sprites and polygons (quads) along with texture mapping and Gouraud shading. It works in conjunction with a second graphics processor, VDP2, to render an image onto the screen.


Rewrite.svg
This article needs to be rewritten.
This article needs to be rewritten to conform to a higher standard of article quality. After the article has been rewritten, you may remove this message. For help, see the How to Edit a Page article.

The Sega Saturn is equipped with dual custom VDP chips for graphics processing. The VDP 1 chip is primarily responsible for sprite generation. Polygon generation is accomplished through manipulation of the sprite engine. Texture mapping and Gouraud shading is also handled by the VDP1. The VDP1 relies on a dual frame buffer that handles rotation and stores textures in special 512K cache.

Both the VDP1 and VDP2 32-bit background and scroll plane video display processor have direct access to the both SH2s, as well as direct memory access (DMA) to both the main and video RAM.

Overview

The VDP1 was based on the Sega Model series, with a quad polygon engine based on the Model 1, along with the Model 2's textured mapping capability. The VDP1 is capable of drawing more polygons than the Model 1, but less than the Model 2. The VDP1 rendered quad polygons, which, despite being used by the most powerful gaming system at the time (Sega Model 2 arcade system), was not industry standard for 3D graphics, compared to the more widely used triangle polygons. The VDP1's quad polygons are drawn with edge anti‑aliasing (for smoother edges), forward texture mapping (a form of perspective correction), bilinear approximation (reduces texture warping), and medium polygon accuracy (resulting in seamless polygons).[1]

The VDP1 had issues with transparency. The VDP1 supports per-pixel transparency between different polygons/sprites in the VDP1 framebuffer, or between VDP1 and VDP2 layers, but not both at the same time, with the VDP2's transparency overriding the VDP1's transparency. In addition, the VDP1 takes six times longer to draw transparent pixels than opaque pixels.[2] There are several ways to overcome the VDP1's transparency issues. The most common method used by Saturn games is to fake transparency with dithering, using a mesh that gets blended by a television's Composite or S-Video cable. Another method is to use the VDP2's hardware transparency, by using a VDP2 bitmap layer as an additional transparent framebuffer, copying transparent assets from the VDP1 framebuffer to a VDP2 bitmap framebuffer layer (e.g. the transparent polygons in Burning Rangers). Another method is software transparency, programming the CPU with software code.

The Saturn's VDP1 was the basis for Nvidia's first graphics processor, the NV1, which was one of the first 3D graphics accelerators on PC, released in 1995. Like the Saturn, it uses quad polygons and supports forward texture mapping with limited perspective correction, and several Saturn ports are available for it. However, the NV1 has a fillrate of 12.5 MPixels/s and a rendering performance of 50,000 polygons/sec, less than the VDP1's 28.4375–57.2728 MPixels/s fillrate and 500,000 polygons/sec rendering performance. In comparison, the most powerful PC graphics card of 1995, Yamaha's Tasmania 3D, which was based on triangle polygons, had a 25 MPixels/s fillrate and 300,000 polygons/sec rendering throughput, more than the NV1, but less than the VDP1.

The VDP1's 3D polygons could be programmed to utilize per-vertex colored lighting and RGB point lights, such as in Panzer Dragoon Saga.

Technical specifications

  • VDP1 @ 28.63636 MHz: Handles sprite/texture and polygon drawing,[3] color calculation and shading,[4] geometry[5]
    • Versions: Sega 315‑5883 (Hitachi HD64440) Video Display Processor 1 (VDP1),[6] Sega 315‑5689 VDP1[4]
    • Adjustable video clock rate: 28.63636 MHz or 26.8465875 MHz (NTSC),[7][8] 28.4375 MHz or 26.8426 MHz (PAL)[7]
    • Parallel bus structure: 3 parallel data buses (dual framebuffers, polygon/texture/sprite RAM), 48-bit bus width (16-bit per bus),[9] 171.8184 MB/s bandwidth[fn 1]
    • Parallel bus cycles: 85.90908 million bus cycles/sec[fn 2]
  • Rendering engine for primitives: textured and untextured polygons, untextured polylines and lines
  • Sprites are textured polygons with specific rendering modes:
    • Normal sprite (one point), shrunk/scaled sprite (two points), quadrangle (four points)
  • Other rendering modes:
    • Overwrite (replace framebuffer contents)
    • Shadow (underlying framebuffer pixels rewritten with 1/2 brightness, primitive not drawn)
    • Half luminosity (primitive rendered with 1/2 brightness)
    • Half transparency (primitive and underlying framebuffer pixels averaged together)
    • Gouraud shading for RGB-format textures only
  • Dual 256 KB frame buffers
    • Programmable frame buffer depth of 8 or 16 bits per pixel
    • Automatic erase feature to clear framebuffer with single color
  • 60 frames of animation per second
  • Color palette: 32,768 colors (15-bit RGB) to 16,777,216 (24-bit VDP2 CRAM palette, accessible by VDP1)[11]
    • Colors on screen: 32,768 colors (15-bit RGB) to 1,048,576 colors (15-bit RGB, 32 transparency levels using VDP2 palette)[12]
    • Colors per pixel: 32,768 colors (16bpp, 15-bit RGB), 256 colors (8bpp, 8-bit palette)
  • Features: Alpha blending, clipping, luminance,[13] shadows,[14] transparency[15] (3 alpha levels, or 32 alpha levels using VDP2 palette),[12] per-pixel transparency[2]
  • Framebuffer capabilities: Double buffering, dual 256 KB framebuffers, rotation & scaling,[13] VDP1 framebuffer can be rotated as bitmap layer by VDP2[19]
    • Framebuffer resolution: 512×256, 512×512, 1024×256[20]
    • Overscan resolution: 1708×263 (NTSC), 1820×313 (PAL), 852×525 (31KC), 848×562 (HDTV)[21]
  • Sprite/Texture capabilities: Rotation & scaling, flipping, distortion,[3][13] warping, vertical and horizontal line scrolling, virtually unlimited color lookup tables,[5][22] System 24/32 sprite rendering system[23]
    • Sprite/Texture size: 8×1 to 504×255 texels[24]
    • Colors per sprite/texture in Lo-Res: 16, 64, 128, 256, and 32,768[25]
    • Colors per sprite/texture in Hi-Res: 16, 64, 128, and 256[26]
    • Maximum texels per scanline: 1812 (NTSC),[7] 1820 (PAL)[21]
    • Maximum sprites/textures per scanline: 226 (NTSC), 227 (PAL)
  • Sprite/Texture/Polygon RAM: 512 KB[27]
    • Sprite/Polygon size: 32 bytes (flat shading),[28][29] 40 bytes (Gouraud shading),[30] 64–96 bytes (shadows),[2] 72–104 bytes (shadows, Gouraud shading)
    • Texture size: 4 bytes (8×1 texels, 16 colors) to 251.02 KB (504×255 texels, 32,758 colors)[29]
    • Maximum sprites per frame: 16,383 (virtually unlimited),[5] 13,106 (Gouraud shading), 5461–8191 (shadows)
    • Maximum polygons per frame: 16,384 (flat shading), 16,383 (texture mapping), 13,107 (Gouraud shading), 13,106 (texture mapping, Gouraud shading), 8192 (shadows), 8191 (texture mapping, shadows), 7281 (texture mapping, shadows, Gouraud shading)
  • Framebuffer fillrate: 28.63636 MPixels/s (16bpp),[fn 3] 35.6465 MPixels/s (8bpp)[fn 4]
  • Texture mapping fillrate: 28.53144 MTexels/s (504×255 textures), 18.205888 MTexels/s (8×8 textures)[fn 6]
    • Gouraud shading: 28.40292 MTexels/s (504×255 textures), 10.373888 MTexels/s (8×8 textures)[fn 7]
  • Polygon rendering performance: Lighting[28][36]
    • 800,000 polys/s: Flat shading, 35-pixel polygons
    • 500,000 polys/s: Flat shading,[37][5] 57-pixel polygons
    • 300,000 polys/s: Gouraud shading,[38][35][34] 32-pixel polygons
  • Texture mapping performance: Lighting[34][38][35]
    • 500,000 polys/s: 32-texel textures
    • 200,000 polys/s:[37][5] Gouraud shading, 40-texel textures
    • 150,000 polys/s: Gouraud shading, shadows, translucency, 32-texel textures

Errata

VDP1 transparency rendering quirk causes strips of pixels to be rewritten to framebuffer for 2-point (scaled) and 4-point (quadrangle) "sprites", applying the transparency effect multiple times. Rarely seen in commercial games (e.g. Robotica explosions), later titles implemented software transparency to correctly render transparent polygons (e.g. Dural in Virtua Fighter Kids).

The VDP1 supports per-pixel transparency between different polygons/sprites in the VDP1 framebuffer, or between VDP1 and VDP2 layers, but not both at the same time, with the VDP2's transparency overriding the VDP1's transparency. There are several ways to overcome this issue. The most common method used by Saturn games is to fake transparency with dithering, using a mesh that gets blended by a television's Composite or S-Video cable. Another method is using a VDP2 bitmap layer as an additional transparent framebuffer, copying transparent assets from the VDP1 framebuffer to a VDP2 bitmap framebuffer layer (e.g. the transparent polygons in Burning Rangers). Another method is software transparency, programming the CPU with software code.

Another issue is that the VDP1 takes six times longer to draw translucent pixels than opaque pixels.[2] The VDP2, in comparison, has no issues with transparency, nor does the use of transparency affect the VDP2's performance. The VDP1 can overcome its transparency performance issue by drawing paletted sprites/polygons, which use the VDP2's palette and transparency, without affecting performance. However, this wouldn't allow multi-layered transparency between sprites/polygons, which would require the use of the methods mentioned above.

Foototes

  1. [57.27272 MB/s per bus 57.27272 MB/s per bus]
  2. [28.63636 MHz polygon/texture/sprite RAM, 28.63636 MHz draw/render framebuffer, 28.63636 MHz display/erase framebuffer[10] 28.63636 MHz polygon/texture/sprite RAM, 28.63636 MHz draw/render framebuffer, 28.63636 MHz display/erase framebuffer[10]]
  3. [1 cycle per pixel[7][31][21] 1 cycle per pixel[7][31][21]]
  4. [28.63636 MPixels/s draw, 14.418 MPixels/s erase/write[32][33] 28.63636 MPixels/s draw, 14.418 MPixels/s erase/write[32][33]]
  5. [Takes six times longer when using VDP1's RGB mode.[2] When using VDP2 palette mode, the VDP1 draws shadowed/translucent objects at full speed. Takes six times longer when using VDP1's RGB mode.[2] When using VDP2 palette mode, the VDP1 draws shadowed/translucent objects at full speed.]
  6. [85.90908 million bus cycles/sec, 222 textured 504×255 polygons/sec (386,905 cycles per polygon), 284,467 textured 8×8 polygons/sec (302 cycles per polygon)[34] 85.90908 million bus cycles/sec, 222 textured 504×255 polygons/sec (386,905 cycles per polygon), 284,467 textured 8×8 polygons/sec (302 cycles per polygon)[34]]
  7. [85.90908 million bus cycles/sec, 221 textured 504×255 polygons/sec (387,137 cycles per polygon), 162,092 textured 8×8 polygons/sec (530 cycles per polygon)[34][35] 85.90908 million bus cycles/sec, 221 textured 504×255 polygons/sec (387,137 cycles per polygon), 162,092 textured 8×8 polygons/sec (530 cycles per polygon)[34][35]]

References

  1. 1.0 1.1 Sega Saturn 3D Capabilities
  2. 2.0 2.1 2.2 2.3 2.4 2.5 File:ST-013-R3-061694.pdf, page 110
  3. 3.0 3.1 3.2 File:ST-013-R3-061694.pdf
  4. 4.0 4.1 4.2 File:Sega Service Manual - Sega Saturn (PAL) - 013-1 - June 1995.pdf
  5. 5.0 5.1 5.2 5.3 5.4 File:NextGeneration US 24.pdf, page 64
  6. Sega Saturn (MAME)
  7. 7.0 7.1 7.2 7.3 File:ST-013-R3-061694.pdf, page 52
  8. Sega Saturn hardware notes (2004-04-27)
  9. File:Sega Service Manual - Sega Saturn (PAL) - 013-1 - June 1995.pdf, page 34
  10. File:ST-013-R3-061694.pdf, page 6
  11. File:TUTORIAL.pdf, page 11
  12. 12.0 12.1 File:ST-TECH.pdf, page 147
  13. 13.0 13.1 13.2 STV VDP1 (MAME)
  14. File:ST-TECH.pdf, page 135
  15. File:ST-013-R3-061694.pdf, page 34
  16. File:ST-238-R1-051795.pdf
  17. 17.0 17.1 File:ST-238-R1-051795.pdf, page 232
  18. File:ST-013-R3-061694.pdf, page 24
  19. File:ST-058-R2-060194.pdf, page 177
  20. File:ST-013-R3-061694.pdf, page 149
  21. 21.0 21.1 21.2 File:ST-013-R3-061694.pdf, page 64
  22. Sega Saturn Tech Specs
  23. Sega System 24 Hardware Notes (2013-06-16)
  24. File:ST-013-R3-061694.pdf, page 119
  25. File:ST-013-R3-061694.pdf, page 18
  26. File:ST-013-R3-061694.pdf, page 29
  27. File:ST-013-R3-061694.pdf, page 81
  28. 28.0 28.1 File:ST-013-R3-061694.pdf, page 40
  29. 29.0 29.1 File:ST-013-R3-061694.pdf, page 75
  30. File:ST-013-R3-061694.pdf, page 39
  31. File:ST-013-R3-061694.pdf, page 35
  32. File:ST-013-R3-061694.pdf, page 65
  33. File:ST-013-R3-061694.pdf, page 61
  34. 34.0 34.1 34.2 34.3 File:TUTORIAL.pdf, page 8
  35. 35.0 35.1 35.2 Saturn VDP1 hardware notes (2003-05-17)
  36. File:TUTORIAL.pdf, page 15
  37. 37.0 37.1 File:SegaVisions US 24.pdf, page 14
  38. 38.0 38.1 File:ST-013-R3-061694.pdf, page 41