Texture Environment (TEV)

The texture environment (TEV) is responsible for blending vertex colors and textures through a fixed function pipeline of at most 16 stages. These stages are the closest thing to shaders in the GX.

Stages

A TEV stage performs a configurable operation on some color inputs and generates an output color that can be fed into the next stage. Stages are executed sequentially. The output of the last stage is the final color.

The TEV has a set of 4 registers, called R0, R1, R2 and R3 (also called PREV), which are shared between all stages and can be used as either input or output of each one of them. Since the color and alpha components are computed separatedly, they can be referred to as R0C, R0A, R1C, R1A, etc.

TEV stages operate on normalized floating-point RGBA color values (i.e. each channel has a value in [0, 1]). The alpha channel is special and can be configured separatedly.

Each TEV stage has 4 input values A, B, C and D. It has only one output, which will be called OUT. The operation of a TEV stage is always of the following form:

value = [sign * (A * (1.0 - C) + B * C) + D + bias] * scale
if (clamp)
    OUT = clamp(value)
else
    OUT = value

In the operation, sign, bias, scale and clamp are configurable:

Inputs

Each input value (A, B, C and D) can be configured to be sourced from one of the following values for the color operation:

And one of the following values for the alpha operation:

The texture and rasterizer colors available to a given stage are also configurable.

Outputs

The output value (OUT) can only be put into one of the 4 TEV registers (R0, R1, R2 and R3).

Register formats

TEV Stage Color

This is the format of the GX registers for TEV stages color configuration:

Bias value selection:

Scale value selection:

Destination register selection:

TEV Stage Alpha

This is the format of the GX registers for TEV stages alpha configuration: