Table of Contents Glide Programming Guide

5Texture Memory

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  Determine how much memory is required for the texture.
  
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  Determine the starting address and extent of free space. Is it adequate for the texture? Will a mipmap level straddle the 2Mbyte boundary in texture memory (thereby causing an error)?
  
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  Download the texture.
  
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  Identify the texture as the texel source for subsequent texture mapping operations.
  

6Computing the Size of a Mipmap

The Glide functions grTexCalcMemRequired() and grTexTextureMemRequired() determine the storage requirements of a mipmap. Textures must start on an 8-byte boundary in memory. The size returned by these functions includes any bytes required to pad the texture to an 8-byte boundary, and may be added to the starting address of the texture to determine the next available location in texture memory.
Both routines use the texture format, aspect ratio, and range of LODs in the mipmap to compute the size. These values are arguments to grTexCalcMemRequired(); they are extracted from a GrTexInfo structure that is passed to grTexTextureMemRequired(). The other difference between the two routines is that grTexTextureMemRequired() has an evenOdd argument and can determine the memory requirements of a texture that will be split across two TMUs for trilinear filtering applications (see Example Texture Mapping.3 in the previous chapter).

25. 
    Table Managing Texture Memory.2 Glide constants that specify arguments to grTex functions.
    

The table below lists the constants used to name the values that can be specified as arguments to functions in the grTex family. The first column lists the argument names that are used in the function specifications. The second column gives the Glide type for the argument. The third column lists the constant name, and the fourth column gives a description.

If the function argument is named	and its type is	then these constants are valid values	and these are the consequences of choosing that value.
tmu	GrChipID_t	GR_TMU0 GR_TMU1 GR_TMU2	Selects the target TMU. The constant names it.
smallLOD largeLOD thisLOD	GrLOD_t	GR_LOD_256 GR_LOD_128 GR_LOD_64 GR_LOD_32 GR_LOD_16 GR_LOD_8 GR_LOD_4 GR_LOD_2 GR_LOD_1	The number in the constant is the largest of the texture. The aspect ratio determines the smaller dimension.
aspectRatio	GrAspectRatio_t	GR_ASPECT_8x1 GR_ASPECT_4x1 GR_ASPECT_2x1 GR_ASPECT_1x1 GR_ASPECT_1x2 GR_ASPECT_1x4 GR_ASPECT_1x8	The constant sets the aspect ratio of the textures in a mipmap.
format	GrTextureFormat_t	GR_TEXFMT_RGB_332 GR_TEXFMT_YIQ_422 GR_TEXFMT_ALPHA_8 GR_TEXFMT_INTENSITY_8 GR_TEXFMT_ALPHA_INTENSITY_44 GR_TEXFMT_P_8 GR_TEXFMT_ARGB_8332 GR_TEXFMT_AYIQ_8422 GR_TEXFMT_RGB_565 GR_TEXFMT_ARGB_1555 GR_TEXFMT_ARGB_4444 GR_TEXFMT_ ALPHA_INTENSITY_88 GR_TEXFMT_AP_88	See Table Managing Texture Memory.1 for a description of the texture formats.
evenOdd	FxU32	GR_MIPMAPLEVELMASK_EVEN GR_MIPMAPLEVELMASK_ODD GR_MIPMAPLEVELMASK_BOTH	Even LODs are GR_LOD_256, GR_LOD_64, GR_LOD_16, GR_LOD_4, and GR_LOD_1. Odd LODs are GR_LOD_128, GR_LOD_32, GR_LOD_8, and GR_LOD_2.
range	GrTexBaseRange_t	GR_TEXBASE_256 GR_TEXBASE_128 GR_TEXBASE_64 GR_TEXBASE_32_TO_1	Specifies the base register when using more than one. A mipmap can be broken into four fragments. The number in the constant corresponds to the LOD number.
tableType table	GrTexTable_t	GR_TEX_NCC0 GR_TEX_NCC1 GR_TEX_PALETTE	Each TMU can have two NCC tables and a palette. Load them one at a time with a general purpose routine.
mipmapMode mode	GrMipMapMode_t	GR_MIPMAP_DISABLE GR_MIPMAP_NEAREST GR_MIPMAP_NEAREST_DITHER	Specifies the kind of mipmapping to perform.

FxU32 grTexCalcMemRequired( GrLOD_t smallLOD,
GrLOD_t largeLOD,
GrAspectRatio_t aspectRatio,
GrTextureFormat_t format

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