樱花大战资源分析之四 DC上的PVR格式

最新推荐文章于 2021-11-18 09:27:15 发布

leexuany

最新推荐文章于 2021-11-18 09:27:15 发布

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分类专栏：资源分析文章标签： image header colors byte table file

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本文详细介绍了Dreamcast游戏机使用的PVR图形格式的技术细节，包括文件头、图像类型及数据布局等，并针对不同像素格式和数据类型进行了具体说明。

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DC支持一种PVR格式，这种格式在很多DC移植到PC的游戏中依然保留。比如樱花大战2还有最近正在汉化的风来之西林外传。

注意，这里说的是老版的PVR格式。这里转载一篇老版的格式说明。

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. ________________________________________________________________________ HEADER ________________________________________________________________________ [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 ________________________________________________________________________ [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 ________________________________________________________________________ [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 ________________________________________________________________________ [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. ________________________________________________________________________ [IMAGE DATA] ________________________________________________________________________ [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