GXSetArray

Syntax

#include <revolution/gx.h>

void GXSetArray( GXAttr attr, const void* base_ptr, u8 stride );

Arguments

attr

Specifies the attribute array name.
Accepted values are:

Attributes	Description
GX_POS_MTX_ARRAY	Array of position coordinate matrices.
GX_NRM_MTX_ARRAY	Array of normal matrices.
GX_TEX_MTX_ARRAY	Texture matrix array.
GX_LIGHT_ARRAY	Light object array.
GX_VA_POS	Position coordinates array.
GX_VA_NRM or GX_VA_NBT	Normal, or normal/binormal/tangent array.
GX_VA_CLR0	Color 0 array.
GX_VA_CLR1	Color 1 array.
GX_VA_TEX0	Texture coordinate 0 array.
GX_VA_TEX1	Texture coordinate 1 array.
GX_VA_TEX2	Texture coordinate 2 array.
GX_VA_TEX3	Texture coordinate 3 array.
GX_VA_TEX4	Texture coordinate 4 array.
GX_VA_TEX5	Texture coordinate 5 array.
GX_VA_TEX6	Texture coordinate 6 array.
GX_VA_TEX7	Texture coordinate 7 array.

base_ptr

Pointer to the first element in the attribute data array.

stride

Stride in bytes between the attribute data elements.

Return Values

None.

Description

This function sets the array base pointer and stride for a single attribute. The array base and stride are used to calculate the address of the indexed attribute data using the following equation:

attr_addr = base_ptr + attr_idx * stride

When drawing a graphics primitive that has been enabled to use indexed attributes (see the GXSetVtxDesc function), attr_idx is supplied in the vertex data. The format and size of the data in the array must also be described in the GXSetVtxAttrFmt function.

You can also index other data, such as matrices (see the GXLoadPosMtxIndx,GXLoadNrmMtxIndx3x3 andGXLoadTexMtxIndx functions), and light objects (see the GXLoadLightObjIndx function). For matrices and light objects, the size and format of the data to be loaded is implied by the function call.

There is a base pointer, base_ptr, for each type of attribute as well as for light data and matrices. Each attribute can be stored in its own array for maximum data compression (i.e., removal of redundant attribute data). The stride is in byte units and indicates the distance between attributes in the array.

Indexed data is loaded into a vertex cache in the graphics processor. The vertex cache fetches 32 bytes of data for each cache miss. As a result, there is a small performance benefit in aligning attribute arrays to 32 bytes, and in arranging vertex data so that it doesn't span 32-byte boundaries. Conveniently enough, the OSAlloc function returns 32-byte aligned pointers. For static data arrays, the ATTRIBUTE_ALIGN(32) macro (for the MetroWerks compiler) can be used to align base_ptr to 32 bytes, as in:

u32 mydata[] ATTRIBUTE_ALIGN(32) = { // initialize data };

Revision History

2006/08/10 Corrected mistake with enum type.
2006/03/01 Initial version.