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The transform unit (XF) is a component of the Wii's GX subsystem. It is responsible for transforming the incoming vertices to screen coordinates.
The transform unit (XF) is a component of the Wii's GX subsystem. It is responsible for transforming the incoming vertices to screen coordinates.
+
+==Writing to XF registers==
+Writing to XF registers is done by writing values to the FIFO, as shown below:
+
+
+To write to '''one''' XF register:
+* write 0x10 (8-bit)
+* write 0x0000 (16-bit)
+* write the address of the register (16-bit)
+* write the value to write to the register (32-bit)
+
+
+To write to '''multiple''' XF registers:
+* write 0x10 (8-bit)
+* write (n-1) (16-bit)
+* write the address of the first register (16-bit)
+* write the values to write to each register (32-bit each)
+Where n is the number of registers to write.
+
+
+==XF registers==
+===XF viewport registers===
+
+These registers define the viewport coordinates.
+
+
+{{regsimple | GX_XF_VIEWPORT_X0 | addr=0x101A | bits=32 | access = R/W}}
+* This register defines the X0 coordinate of the viewport.
+
+
+{{regsimple | GX_XF_VIEWPORT_Y0 | addr=0x101B | bits=32 | access = R/W}}
+* This register defines the Y0 coordinate of the viewport.
+
+
+{{regsimple | GX_XF_VIEWPORT_Z | addr=0x101C | bits=32 | access = R/W}}
+* This register defines the depth (far plane - near plane) of the viewport.
+
+
+{{regsimple | GX_XF_VIEWPORT_X1 | addr=0x101D | bits=32 | access = R/W}}
+* This register defines the X1 coordinate of the viewport.
+
+
+{{regsimple | GX_XF_VIEWPORT_Y1 | addr=0x101E | bits=32 | access = R/W}}
+* This register defines the Y1 coordinate of the viewport.
+
+
+{{regsimple | GX_XF_VIEWPORT_FP | addr=0x101F | bits=32 | access = R/W}}
+* This register defines the far plane of the viewport.
+
+
+The viewport coordinates can be calculated as shown below:
+* GX_XF_VIEWPORT_X0 = viewport_width / 2
+* GX_XF_VIEWPORT_Y0 = (-viewport_height) / 2
+* GX_XF_VIEWPORT_X1 = (viewport_x + (viewport_width / 2)) + 342
+* GX_XF_VIEWPORT_Y1 = (viewport_y + (viewport_height / 2)) + 342
+* GX_XF_VIEWPORT_FP = viewport_farplane * 16777215
+* GX_XF_VIEWPORT_Z = (viewport_farplane - viewport_nearplane) * 16777215
+''Note: These formulas are taken from the libogc function GX_SetViewportJitter().''
+
+
+GX_XF_VIEWPORT_FP and GX_XF_VIEWPORT_Z are 24-bit fixed-point values ranging between 0 and 16777215. These numbers respectively represent 0.0 and 1.0 in floating-point.
+
+All the other viewport registers are 32-bit floating-point values.
+
+===XF projection registers===
+
+These registers define the projection matrix.
+Actually, there are 7 registers, so they don't really define a matrix, but rather parts of it.
+
+
+{{regsimple | GX_XF_PROJ_0 | addr=0x1020 | bits=32 | access = R/W}}
+{{regsimple | GX_XF_PROJ_1 | addr=0x1021 | bits=32 | access = R/W}}
+{{regsimple | GX_XF_PROJ_2 | addr=0x1022 | bits=32 | access = R/W}}
+{{regsimple | GX_XF_PROJ_3 | addr=0x1023 | bits=32 | access = R/W}}
+{{regsimple | GX_XF_PROJ_4 | addr=0x1024 | bits=32 | access = R/W}}
+{{regsimple | GX_XF_PROJ_5 | addr=0x1025 | bits=32 | access = R/W}}
+* These registers define 6 projection values.
+
+
+{{regsimple | GX_XF_PROJ_MODE | addr=0x1026 | bits=32 | access = R/W}}
+* This register defines how the projection values will be translated.
+
+
+Depending on GX_XF_PROJ_MODE, you must assign different parts of your 4x4 projection matrix to the projection values:
+* GX_XF_PROJ_MODE = 0 (perspective):
+** GX_XF_PROJ_0 = matrix[0][0]
+** GX_XF_PROJ_1 = matrix[0][2]
+** GX_XF_PROJ_2 = matrix[1][1]
+** GX_XF_PROJ_3 = matrix[1][2]
+** GX_XF_PROJ_4 = matrix[2][2]
+** GX_XF_PROJ_5 = matrix[2][3]
+* GX_XF_PROJ_MODE = 1 (orthographic):
+** GX_XF_PROJ_0 = matrix[0][0]
+** GX_XF_PROJ_1 = matrix[0][3]
+** GX_XF_PROJ_2 = matrix[1][1]
+** GX_XF_PROJ_3 = matrix[1][3]
+** GX_XF_PROJ_4 = matrix[2][2]
+** GX_XF_PROJ_5 = matrix[2][3]
+''Note: these assignments are taken from the libogc function GX_LoadProjectionMtx().''