PVR Graphic Formats (Dreamcast 2D Graphics)
By SmokesGrass:|
http://www.thehorrorisalive.com/markgrass/index.html
Version 0.1 - March 03, 2006
- Highly updated version from original 2001 document by an unknown person.
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HEADER
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[GLOBAL INDEX HEADER]
This header is optional defining a "Global Index".
offset length description
--------------------------
0-3 4 "GBIX" (ascii text)
4-7 4 Length of GBIX header from offset 8 onwards
8-15 8 Global Index
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[PVR GRAPHIC HEADER]
offset length description
--------------------------
0-3 4 "PVRT" (ascii text)
4-7 4 Length of rest of file in bytes (not counting these 4 bytes)
8-11 4 Type of PVR file
12-13 2 Width
14-15 2 Height
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[PVR GRAPHIC TYPE]
There are 4 bytes reserved for the PVR type. Byte 1 identifies the Pixel Format. Byte 2 identifies the Image Data Type. Bytes 3 & 4 are blank (0x0000).
The 2 bytes for each type are as follows:
byte 1 (Pixel Format):
0x00 = ARGB1555 (bilevel translucent alpha 0,255)
0x01 = RGB565 (no translucent)
0x02 = ARGB4444 (translucent alpha 0-255)
0x03 = YUV442
0x04 = Bump
0x05 = 4-BIT (SEE BELOW)
0x06 = 8-BIT (SEE BELOW)
:4-BIT/8-BIT FORMAT:
The Dreamcast uses a PowerVR graphics chip which requires 4/8-BIT images to be "twiddled" before blending, therefore 4/8-BIT images are always twiddled. Also, not every 4/8-BIT PVR image uses a CLUT.
byte 2 (Image Data Type):
0x00 =
0x01 = SQUARE TWIDDLED
0x02 = SQUARE TWIDDLED & MIPMAP
0x03 = VQ
0x04 = VQ & MIPMAP
0X05 = 8-BIT CLUT TWIDDLED
0X06 = 4-BIT CLUT TWIDDLED
0x07 = 8-BIT DIRECT TWIDDLED
0X08 = 4-BIT DIRECT TWIDDLED
0x09 = RECTANGLE
0x0A =
0x0B = RECTANGULAR STRIDE
0x0C =
0x0D = RECTANGULAR TWIDDLED
0x0E =
0x0F =
0x10 = SMALL VQ
0x11 = SMALL VQ & MIPMAP
0x12 = SQUARE TWIDDLED & MIPMAP
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[WIDTH AND HEIGHT]
The width and height of every PVR image is setup in multiples of 256 with 4 bytes total representing both width and height.
The 2 bytes representing both BPP values are as follows:
0x0000 = 0
0x0001 = 256
0x0002 = 512
0x0003 = 768
0x0004 = 1024
....and so on.
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[IMAGE DATA]
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[PIXEL TYPE]
There are 7 different pixel image types used in PVR graphics that immediately follow the PVR header.
0x05 (4-BIT):
4-BIT images use a 1024 byte table for RGB colors which makes 64 possible 16-color palettes.
offset length description
--------------------------
0-3FF 1024 CLUT
400-? ? Image Data
0x06 (8-BIT):
8-BIT images use a 1024 byte table for RGB colors which makes 4 possible 256-color palettes.
offset length description
--------------------------
0-3FF 1024 CLUT
400-? ? Image Data 
