GXSetIndTexMtx

Syntax

#include <revolution/gx.h>

void GXSetIndTexMtx(
    GXIndTexMtxID   mtx_sel,
    const f32       offset_mtx[2][3],
    s8              scale_exp );

Arguments

mtx_sel

The indirect matrix that is being affected. Accepted values are:

Name	Indirect matrix
GX_ITM_0	Indirect matrix 0 and matrix scale value 0.
GX_ITM_1	Indirect matrix 1 and matrix scale value 1.
GX_ITM_2	Indirect matrix 2 and matrix scale value 2.

offset_mtx

Value assigned to the indirect matrix. Each component must fall in the range -1 ≦ x ≦ +1.

scale_exp

Exponent of 2 to assign to the scale factor. The exponent must fall in the range -17 ≦ x ≦ +46. Since the output values are stored in a S17.7 format, take notice of the range of output values to avoid overflow when you use large or small scale factor.

Return Values

None.

Description

This function lets you set one of the three static indirect matrices and the associated scale factor. The indirect matrix and scale is used to process the results of an indirect lookup in order to produce offsets to use during a regular lookup. The matrix is multiplied by the [S T U] offsets that have been extracted (and optionally biased) from the indirect lookup color. In this matrix-vector multiply, the matrix is on the left and the [S T U] column vector is on the right.

The matrix values are stored in the hardware as a sign and 10 fractional bits (two's complement). Thus the smallest number that can be stored is -1 and the largest is (1 - 1/1024) or approximately 0.999. Since +1 cannot be stored, you may consider dividing all the matrix values by two (thus +1 becomes +0.5) and adding one to the scale value in order to compensate.

Revision History

2006/03/01 Initial version.