Sound: DefineEnvelope

       Name: DefineEnvelope                                          [Show more]
       Type: Subroutine
   Category: Sound
    Summary: Define a sound envelope
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * MakeSound calls DefineEnvelope


 Arguments:

   A                    The number of the sound envelope data block to define in
                        the envelopeData table (0 to 5)


.DefineEnvelope

 STA aStoreEnvelope     \ Set (Y X) = envelopeData + (A * 8 - A) * 2
 ASL A                  \           = envelopeData + A * 7 * 2
 ASL A                  \           = envelopeData + A * 14
 ASL A                  \
 SEC                    \ starting with the low byte (we set the high byte in
 SBC aStoreEnvelope     \ MakeSoundEnvelope)
 ASL A                  \
 ADC #LO(envelopeData)  \ Each envelope definition in envelopeData contains 14
 TAX                    \ bytes of data, so this sets A to the address within
                        \ the envelopeData table of the data for the envelope
                        \ number in A

 LDA #8                 \ Set A = 8 for the OSWORD command to define an envelope

                        \ Fall through into MakeSoundEnvelope to set up Y and
                        \ apply the OSWORD command to the (Y X) block, which
                        \ defines the relevant sound envelope