#include <revolution/gx.h>
void GXSetTexCoordGen(
GXTexCoordID dst_coord,
GXTexGenType func,
GXTexGenSrc src_param,
u32 mtx );
| dst_coord | Name of the texture coordinate to be generated. Accepted values are: GX_TEXCOORD0, GX_TEXCOORD1, GX_TEXCOORD2 through GX_TEXCOORD7. |
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| func | Feature used to generate texture coordinates. Accepted values are:
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| src_param | Name of source attributes used to generate texture coordinates.
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| mtx |
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None.
This function is used to specify how texture coordinates are generated. Output texture coordinates are usually the result of some transform of an input attribute, either for position, normal, or texture coordinates. You can also generate texture coordinates from the output color channel for vertex lighting calculations. This function also supports the embossed style of bump-mapping. In C-language syntax the texture coordinate generation function would look like this:
dst_coord = func(src_param, mtx);
The current vertex descriptor as set by the GXSetVtxDesc function only describes the data input to the graphics processor. Using the GXSetTexCoordGen function, you can create new output texture coordinates from the input data. The dst_coord argument is used to give the output texture coordinate a name. This texture coordinate can be bound to a texture using the GXSetTevOrder function. The GXSetNumTexGens function specifies a consecutive number of texture coordinates, starting at GX_TEXCOORD0, that is available to the GXSetTevOrder function.
Input texture coordinates must always pass through the texture-coordinate generation hardware. Because, with the GXInit function, the input texture coordinates pass through the texture coordinate generation hardware with no change in their values, you call this function for initialization so that all texture coordinates are transformed by the GX_IDENTITY matrix.
There are eight output texture coordinates that can be referenced in any of the 16 TEV stages. There are a maximum of eight input texture coordinates.
The GXTexMtx enumerator defines a default set of texture matrix names that can be supplied as mtx. The matrix names are actually row addresses (four floating point digits per row) in the matrix memory that indicate the first row of a loaded matrix. Another memory map of matrix memory may be defined to suit user needs. Be aware, however, that modelview matrices (see the GXLoadPosMtxImm and GXPosNrmMtx functions) and texture matrices share matrix memory.
The simplest type (GX_TG_MTX2x4 and GX_TG_MTX3x4) of texture-coordinate generation transforms an input attribute (either position, normal or texture coordinate) and assigns the result to an output-texture coordinate. GX_TG_MTX2x4 performs a 2x4 matrix multiply on the input attribute and generates S and T texture coordinates. GX_TG_MTX3x4 performs a 3x4 matrix multiplication on the input attribute, and generates S, T, and Q texture coordinates. S and T are then divided by Q to produce the actual 2D texture coordinates.
// generate texture coord 0 (S/T/Q) from transform of position (x,y,z)
GXSetTexCoordGen(GX_TEXCOORD0, GX_TG_MTX3x4, GX_TG_POS, GX_TEXMTX0);// generate tex coord 2 (S/T) from transform of position (x,y,z)
GXSetTexCoordGen(GX_TEXCOORD2, GX_TG_MTX2x4, GX_TG_POS, GX_TEXMTX5);// generate tex coord 0 and tex coord 1 (S/T) from input coord 0
GXSetTexCoordGen(GX_TEXCOORD0, GX_TG_MTX2x4, GX_TG_TEX0, GX_IDENTITY);
GXSetTexCoordGen(GX_TEXCOORD1, GX_TG_MTX2x4, GX_TG_TEX0, GX_IDENTITY);// generate tex coord 3 (S/T/Q) from transform of the normal
GXSetTexCoordGen(GX_TEXCOORD3, GX_TG_MTX3x4, GX_TG_NRM, GX_TEXMTX2);// generate tex coord 0 (S/T) from translation/rotation of input coord 0
GXSetTexCoordGen(GX_TEXCOORD0, GX_TG_MTX2x4, GX_TG_TEX0, GX_TEXMTX1);This type of texture coordinate generation can be used to create cartoon lighting effects. One of the color channel results is converted into texture coordinates.
The S coordinate is set equal to the 8-bit R (red) component of the channel. The T coordinate is set equal to the 8-bit G (green) component of the color channel. For cartoon lighting, the S coordinate will represent the light intensity and is input to an arbitrary 1D texture look-up to convert intensity to color. The T coordinate is used to represent material color, and is used to select a 1D table from a 2D texture. Texture coordinates generated using GX_TG_SRTG should be generated after all other coordinates. (See the Functional Ordering Requirements section below.)
The texture which represents the array of 1D intensity-to-color tables must be constructed carefully. Each table (row) should be duplicated. Since the S and T coordinates are generated from 8-bit colors, a maximum texture of 256 x 256 can be used. For this texture size, there are 127 tables available. This is equal to ((256-1)/2).
The rule for generating the G channel color which will create a T coordinate centered properly in the two-row table is as follows.
n = 1-D intensity lookup table index (0-126 for a 256x256 texture)
rows = number of rows in the texture, multiple of 2
if ((2*n +1) < ((rows-1)/2))
green = 2*n + 1
else
green = 2*n// convert color0 to s,t for 2-D texture lookup, matrix not used
GXSetTexCoodGen(GX_TEXCOORD2, GX_TG_SRTG, GX_TG_COLOR0, GX_IDENTITY);This type (GX_TG_BUMP0-7) of bump-mapping perturbs input texture coordinates based on normal and light direction information. Use the original and offset texture coordinates to look up texels from the height field bump map. You can subtract these values in the TEV to find the bump height, and then add this value to the final color of the pixel. In bump map calculations, GX_BUMP0 indicates that light 0 will be used, GX_BUMP1 indicates that light 1 will be used, and so on.
The src_param for bump maps is a texture coordinate whose number is smaller than the target texture coordinate. For example, source texture coordinate = GX_TEXCOORD0, and bump offset texture coordinate = GX_TEXCOORD1. Since the source texture is one of the transformed texture coordinates (GX_TG_MTX2x4 or GX_TG_MTX3x4), you can't use a bump map texture coordinate as source for another bump map texture coordinate. Bump map texture coordinates should be generated after coordinates generated from transforms (GX_TG_MTX2x4 and GX_TG_MTX3x4). For more details, see the Functional Ordering Requirements section below.
// source for a bump mapped coordinate, transformed by a matrix
GXSetTexCoordGen(GX_TEXCOORD0, GX_TG_MTX2x4, GX_TG_TEX0, GX_TEXMTX3);
// perturbed coordinate, offset from TEXCOORD0 above,
// light 0. Matrix is not used.
GXSetTexCoordGen(GX_TEXCOORD1, GX_TG_BUMP0, GX_TG_TEXCOORD0, GX_IDENTITY);Texture coordinates must be generated in functional order: All transforms are first (GX_TG_MTX2x4 or GX_TG_MTX3x4), followed by bump maps (GX_TG_BUMP0-3), followed by texture coordinate generation from lighting (GX_TG_SRTG).
Texture coordinates must be generated using sequential texture coordinate numbers starting at GX_TEXCOORD0.
The number of bump map texture coordinates should be equal to or less than three.
Texture coordinate generation from lighting (GX_TG_SRTG) is slightly complicated in its ordering restrictions:
GX_TG_COLOR0 must come first, followed by those with GX_TG_COLOR1.
GX_TG_COLOR1 cannot be used by themselves. There must be coordinates included which use GX_TG_COLOR0.
GX_TG_COLOR0 or GX_TG_COLOR1) for more than one texture coordinate.
When generating texture coordinates using GX_MTX3x4 or GX_MTX2x4, you may pass the matrix index per vertex, rather than using GXSetTexCoordGen. This feature is most often used with skinned (stitching) models. When the matrix index is passed per vertex, the value specified in GXSetTexCoordGen is overwritten, as indicated by the current vertex descriptor. In other words, GXSetTexCoordGen sets a current matrix index that will be replaced by each per-vertex index.
GXSetNumTexGens, GXSetTexCoordGen2, GXSetVtxDesc, GXSetTevOrder
2008/05/23 Touched up the text.
2006/03/01 Initial version.
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