Allow using position and normals as tex coordinates #82
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The registers to be used as texture input coordinates will (in the following commit) computed when setting up the vertex arrays, so this operation must happen before setting up the TEV (which uses those registers). This small refactoring also reduces some code duplication.
The GX_VA_TEX* formats only allow up to two components in the texture input coordinates (s and t), but OpenGL applications can provide up to four, along with a texture matrix to transform them. While we are not able to support this general case (not easily, at least!), we can handle the case where the array with the texture input coordinates is the same passed for the positional or normal attributes, because in that case we can skip re-uploading these coordinates at all and can setup the TEV to read texture coordinates from GX_TG_POS or GX_TG_NRM and transform them with the given matrix. This works well with Neverball, which passes the same array of positions as texture coordinates when it needs to apply the ball shadow to the object lying under the ball.
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Some application (like the Neverball game) specify the same array of positional coordinates to glTexCoordPointer(), and setup an appropriate texture matrix to transform them as needed. But GX only allows submitting up to two components of texture coordinates (s and t), and simply discarding the third component leads to incorrect rendering results.
The solution (which only works in the case the same array pointer is specified both as positional and texture coordinates -- a fully generic solution does not seem to be possible) is to setup the TEV so that texture coordinates are read from the positional array. This requires some refactoring of the array processing code.
Unlike the previous MR, these commits are all related (but can still be reviewed independently).