N64 Programming/Video coprocessor

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The RCP (VDP,PPU,video controller) is mainly interesting for polygon crunching and post-filter effects.

Formed from two components - RSP(Reality Signal Processor) and RDP(Reality Drawing Processor).

Texture cache and framebuffers are shared in RDRAM with the CPU.

Actual texture memory is only 4KB -- only allowed to operate on this amount at a time.

RSP(Reality Signal Processor)[edit]

RSP is your transform and lighting unit (TnL). Manipulates world data and textures.

Mathematically, lots of matrices to transform from local data -> world space -> view space (projection w/ z-perspective correction).

Transform means scaling, translating and rotating for polygons, lighting normals, texture UVs.

Creates primitive lists of triangles and lines for the RDP to render.

RDP(Reality Drawing Processor)[edit]

RDP is the display unit.

Rasterizer, fog, environmental, color blending. Anti-aliasing effects.

Lower-level pixel handler.

uCodes[edit]

The RCP has its own language, dubbed 'uCodes' (256 microcodes).

Think of modern vertex and pixel DirectX shaders - both stages combined.

R4000 coprocessor (COP2). Each uCode is a string of ASM instructions run by the RSP. Also sets up the RDP batch renderer.

Display lists are a sequence of uCodes defined by the game. This is fed to the RSP.


Note: Emulator authors choose to translate uCodes into higher-level languages.

The programmers can define their own vertex / texture formats. Lighting methods. Overdraw detection and other flexible wizardry.

The microcodes are uploaded to the RCP at run-time. So each game has its own library of drawing functions (some are like DSP1 -> DSP1A -> DSP1B and others are akin to DSP2,DSP3).

Texture variations[edit]

Games use custom formats. Furthermore, linear bitmaps can be any size (320x8, 48x13). 4/8/16/32-bpp is the norm.

The microcode libraries tend to define several 'accepted' formats.

This is a sample list from video plugin authors.

  • 16-bit RGBA = 5551. Red,green,blue,alpha (transparency).
  • 32-bit RGBA = 8888.
  • 4-bit IA = 31. Grayscale intensity (luminosity,brightness) + alpha.
  • 8-bit IA = 44.
  • 16-bit IA = 88.
  • 4-bit I = 40. Grayscale only.
  • 8-bit I = 80. Grayscale.
  • 16-bit I = (16)(0).
  • 4-bit CI = 40. Palette lookup --> 16-bit RGBA or 16-bit IA.
  • 8-bit CI = 80. Palette lookup --> 16-bit RGBA or 16-bit IA.

YUV = some other color format. Output is RGB (888) + Full alpha.