GXSetTevAlphaIn

Syntax

#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, ... , GX_TEVSTAGE15.
a 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   Input operand. An unsigned 8-bit value for the element. Applicable values are the same as for a.
c Input operand. An unsigned 8-bit value for the element. Applicable values are the same as for a.
d Input operand. A signed 1-bit + 10-bit value per element. Applicable values are the same 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 GX_TEVPREV register (see GXInit), but can be set explicitly by the GXSetTevAlphaOp function. 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 the GXSetTevColor or GXSetTevColorS10 functions.

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 the GXSetTevOrder function.

See Also

GXSetTevOp, GXSetTevColorIn, GXSetTevAlphaOp, GXSetTevKAlphaSel

Revision History

2008/05/26 Corrected errors.
2006/03/01 Initial version.

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