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⌂ ∞ Lander on the Acorn Archimedes

Maths (Geometry): AddVectorToVertices

       Name: AddVectorToVertices                                     [Show more]
       Type: Subroutine
   Category: Maths (Geometry)
    Summary: Add a vector to the rotated vertex coordinates to get the vertex
             coordinates in 3D space

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * AddVectors calls AddVectorToVertices
             * DrawObject (Part 2 of 5) calls AddVectorToVertices




 Calculate the following:

   [ xCoord ]   [ R0   ] + [ xVertexRotated ]
   [ yCoord ] = [ R0+4 ] + [ yVertexRotated ]
   [ zCoord ]   [ R0+8 ] + [ zVertexRotated ]

 This routine is only ever called with R0 = xObject, so this adds the rotated
 vertex coordinate to the object's coordinate, giving the vertex's coordinate
 in the game's coordinate system.



 Arguments:

   R0                               The address of the 3D vector to add in the
                                    above calculation



 Other entry points:

   AddVectorToVertices+8            Enter the routine with R0 to R3 already set



.AddVectorToVertices

 LDMIA   R0, {R0-R2}                \ Fetch the coordinate from R0 into
                                    \ (R0, R1, R2)

 ADD     R3, R11, #xVertexRotated   \ Set R3 to the address of the coordinates
                                    \ in xVertexRotated

 STMFD   R13!, {R5-R6}              \ Store the registers that we want to use on
                                    \ the stack so they can be preserved

 LDMIA   R3, {R3-R5}                \ Fetch the vector at xVertexRotated into
                                    \ (R3, R4, R5)

 ADD     R0, R0, R3                 \ Set R0 = R0 + R3
                                    \        = R0 + xVertexRotated

 ADD     R1, R1, R4                 \ Set R1 = R1 + R4
                                    \        = R0+4 + yVertexRotated

 ADD     R2, R2, R5                 \ Set R2 = R2 + R5
                                    \        = R0+8 + zVertexRotated

 ADD     R3, R11, #xCoord           \ Store (R0, R1, R2) in (xCoord, yCoord,
 STMIA   R3, {R0-R2}                \ zCoord)

 LDMFD   R13!, {R5-R6}              \ Retrieve the registers that we stored on
                                    \ the stack

 MOV     PC, R14                    \ Return from the subroutine