3D Test Commands

These Commands test various parameters against desired results by the user. Each command requires that the “test busy” bit of the GXSTAT register is cleared before reading the result.

Test if Cuboid Intersects View Volume: Port 0x040005C0, Index 0x70, 3 Parameters

The result of this command can be read from bit 1 of the GXSTAT register and indicates if any part of the specified cuboid intesects the view volume. A value of 1 indicates that the cuboid would have been visible if drawn.

Parameter definition:

all parameters are in the same format as 16 bit vertex coordinates. As in, 1bit sign + 3 bit integer + 12 bit fraction.

Set Coordinates for Position Test: Port 0x040005C4, Index 0x71, 2 Parameters

Takes the vector (x,y,z,1) and multiplies by the positional and projection matrix stacks. Result can be read from the memory region at 0x04000620..=0x0400062F where each word corresponds to a coordinate of the resulting vector. In format 1bit sign + 19 bit integer + 12 bit fraction.

Parameter Definition:

all parameters are in the same format as 16 bit vertex coordinates. As in, 1bit sign + 3 bit integer + 12 bit fraction.

Notes: This command should not be issued while a vertex list is being constructed. As any vertex position commands that inherit the coordinates of the previous vertex will instead inherit the coordinates set by this command.

Set Directional vector for Direction Test: Port 0x040005C8, Index 0x72, 1 Parameter

Takes the vector (x,y,z,0) and multiplies by the directional matrix stack. (according to no$ also requires matrix mode 2?) Result can be read from the memory region at 0x04000630..=0x04000635 where each 2byte half word corresponds to a coordinate of the resulting vector. In format 4bit sign + 12 bit fraction. (sign is either 0b0000 or 0b1111)

Parameter Definition:

all parameters are in the same format as those for other light direction commands, as in: 1bit sign + 9 bit fraction.