GXSetTevAlphaIn

C Specification

#include <revolution/gx.h>

void GXSetTevAlphaIn(
GXTevStageID   stage,
GXTevAlphaArg  a,
GXTevAlphaArg  b,
GXTevAlphaArg  c,
GXTevAlphaArg  d );

Arguments

stage name of the stage
Accepted values are: GX_TEVSTAGE0, GX_TEVSTAGE1, GX_TEVSTAGE2 through GX_TEVSTAGE15.

a

an input operand
An unsigned 8-bit value for the component.
Accepted values are:

Name	Input
`GX_CA_A0`	alpha from the `TEVREG0` register
`GX_CA_A1`	alpha from the `TEVREG1` register
`GX_CA_A2`	alpha from the `TEVREG2` register
`GX_CA_APREV`	alpha from the `TEVPREV` register
`GX_CA_TEXA`	alpha from the texture
`GX_CA_RASA`	alpha from the rasterized vertex color
`GX_CA_ZERO`	0.0 fixed
`GX_CA_KONST`	constant alpha input (see the `GXSetTevKAlphaSel` function)

b an input operand
An unsigned 8-bit value for the element. Applicable values are as for a.

c an input operand
An unsigned 8-bit value for the element. Applicable values are as for a.

d an input operand
A signed 1-bit + 10-bit value for the element. Applicable values are as for a.

Return Values

None.

Description

This function sets the input operands for one stage of the texture environment (TEV) alpha combiner unit. The input operands a, b and c are unsigned 8-bit inputs (0 <= a,b,c <= 255). The d input operand is a signed 10-bit input (-1024 <= d <= 1023).

Each TEV stage implements the following function:

reg = (d (op) ((1.0 - c)*a + c*b) + bias) * scale;

The operations described by op, bias and scale are programmable using the GXSetTevAlphaOp function.

The output of this stage is directed by default to the register GX_TEVPASS (see GXInit), but may be set explicitly by GXSetTevAlphaOp. When the input a, b or c is from a signed 10-bit number (either the results of a previous TEV stage or an input constant), only the 8 least-significant bits are used. The number is not converted; upper bits are simply discarded.

The registers used to store the output of TEV stages can also be used as inputs: GX_CA_A0, GX_CA_A1, GX_CA_A2 and GX_CA_APREV. These registers can be set with constant alpha values using GXSetTevColor or GXSetTevColorS10.

The input operand GX_CA_RASA is the solution for the per-vertex lighting equation. The input operand GX_CA_TEXA is the texture alpha input for this stage. You can select the colors and textures to which these inputs correspond using GXSetTevOrder.

Revision History