GPU Textures

This page describes the GPU commands used for textures.

General information

Individual texels in a texture are laid out in memory as a Z-order curve. Mipmap data is stored directly following the main texture data.

Texture unit setup: Register 0x80

Register 0x80 is used to enable individual texture units.

Bit	Description
0	Enable texture unit 0.
1	Enable texture unit 1.
2	Enable texture unit 2.

Configuration of texture unit 0

Register ID	Description
0x0081	Border color (unverified)
0x0082	Bits 16-31 are the texture width. Bits 0-15 are the texture height. The maximum texture size in either direction is 1024.
0x0083	Texture parameters (filtering, wrapping), see below.
0x0084	LOD setup?
0x0085	Physical address of texture data (divided by 8).
0x0086	Physical address of texture data for cube mapping?
0x0087	Physical address of texture data for cube mapping?
0x0088	Physical address of texture data for cube mapping?
0x0089	Physical address of texture data for cube mapping?
0x008A	Physical address of texture data for cube mapping?
0x008B	Shadow related?
0x008E	Texture format (see below)

Configuration of texture units 1 and 2

Texture units 1 and 2 use a configuration block similar to the one of texture unit 0. They are based at registers 0x0091 and 0x0099.

Index word	Description
0-4	Same as for texture unit 0
5	Texture format (see below)

Configuration of texture unit 3

The configuration block for texture unit 3 seems to be vastly different from the other texture units. Instead, registers 0x00A8 through 0x00B7 are used to configure procedural texturing features.

Texture parameters

Bit	Description	GL parameter name
0	Normally this is value 0.
1	0 = point sampling (GL_NEAREST), 1 = linear interpolation (GL_LINEAR)	GL_TEXTURE_MAG_FILTER
2	0 = point sampling (GL_NEAREST*), 1 = linear interpolation (GL_LINEAR*)	GL_TEXTURE_MIN_FILTER
3	Unused?	?
5-4	2 = texture color type 0xC, 0 otherwise.(Enable/disable texture data compression?) 0 = unknown, 1 = unknown, 3 = same effect as value 2.
7-6	Unused
11-8	0 = GL_CLAMP_TO_EDGE, 1 = GL_CLAMP_TO_BORDER, 2 = GL_REPEAT, 3 = GL_MIRRORED_REPEAT	GL_TEXTURE_WRAP_S
15-12	Same values as GL_TEXTURE_WRAP_S.	GL_TEXTURE_WRAP_T
24	0 = no LOD interpolation (GL_*_MIPMAP_NEAREST), 1 = linear LOD interpolation (GL_*_MIPMAP_LINEAR)	GL_TEXTURE_MIN_FILTER
27-25	Unused?
30-28	When some flag=1: value1=GL_TEXTURE_2D, value0 when the input parameter is not GL_TEXTURE_2D. When some flag=0: 0=GL_TEXTURE_2D, 1-4=unknown.	?
31	Unused?	?

Texture color types

Value	Description	GL Format	GL Data Type
0x0	RGBA8888	GL_RGBA	GL_UNSIGNED_BYTE
0x1	RGB888	GL_RGB	GL_UNSIGNED_BYTE
0x2	RGBA5551	GL_RGBA	GL_UNSIGNED_SHORT_5_5_5_1
0x3	RGB565	GL_RGB	GL_UNSIGNED_SHORT_5_6_5
0x4	RGBA4444	GL_RGBA	GL_UNSIGNED_SHORT_4_4_4_4
0x5	IA8	GL_LUMINANCE_ALPHA	GL_UNSIGNED_BYTE
0x6	HILO8
0x7	I8	GL_LUMINANCE	GL_UNSIGNED_BYTE
0x8	A8	GL_ALPHA	GL_UNSIGNED_BYTE
0x9	IA44	GL_LUMINANCE_ALPHA	GL_UNSIGNED_BYTE_4_4_EXT
0xA	I4
0xB	A4	GL_ALPHA	GL_UNSIGNED_NIBBLE_EXT
0xC	ETC1	GL_ETC1_RGB8_OES
0xD	ETC1A4