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⌂ ∞ ▽ Revs on the BBC Micro

3D objects: GetObjectAngles

       Name: GetObjectAngles                                         [Show more]
       Type: Subroutine
   Category: 3D objects
    Summary: Calculate the object's yaw and pitch angles, and set the object's
             visibility, scale and type
  Deep dive: Pitch and yaw angles

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BuildCarObjects (Part 3 of 3) calls GetObjectAngles
             * BuildCarObjects (Part 3 of 3) calls via GetObjectAngles-2




 Arguments:

   A                    Object type

   X                    The offset of the variable to use for the object's 3D
                        coordinates in the GetObjYawAngle routine:

                          * &F4 = xHelmetCoord

                          * &FA = xCoord1

                          * &FD = xCoord2



 Other entry points:

   GetObjectAngles-2    Use xCoord2 for the object's 3D coordinates in the call
                        to GetObjYawAngle



 LDX #&FD               \ Set X = &FD so the calls to GetObjYawAngle and
                        \ GetObjPitchAngle use xCoord2 and yCoord2 for the
                        \ object's 3D coordinates

.GetObjectAngles

 STA objectType         \ Store the object type in objectType

 JSR GetObjYawAngle-2   \ Calculate the object's yaw angle, from the point of
                        \ view of the player, returning it in (JJ II)

 LDY objectNumber       \ Set Y to the number of the object we are processing

 LDA II                 \ Set the yaw angle for this object in (objYawAngleHi
 STA objYawAngleLo,Y    \ objYawAngleLo) to (JJ II)
 LDA JJ
 STA objYawAngleHi,Y

 JSR CheckForContact-2  \ Check to see if the object and the player's car are
                        \ close enough for contact, specifically if they are
                        \ within a distance of 37 from each other

 JSR GetObjPitchAngle-2 \ Calculate the object's pitch angle, from the point
                        \ of view of the player, returning it in A and LL
                        \
                        \ If the object is not visible on-screen, the C flag is
                        \ set, which will hide the object in the following
                        \ routine

                        \ Fall through into SetObjectDetails to set the object's
                        \ visibility, scale and type