Drawing the screen: SetDrawingBitplane

       Name: SetDrawingBitplane                                      [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Set the drawing bitplane to a specified value
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * FlipDrawingPlane calls SetDrawingBitplane
             * SendViewToPPU calls SetDrawingBitplane
             * SetDrawingPlaneTo0 calls SetDrawingBitplane
             * SetupViewInNMI calls SetDrawingBitplane
             * TT66 calls SetDrawingBitplane


 Arguments:

   X                    The new value of the drawing bitplane


.SetDrawingBitplane

 STX drawingBitplane    ; Set the drawing bitplane to X

 LDA lastPattern,X      ; Set the next free pattern number in firstFreePattern
 STA firstFreePattern   ; to the number of the last pattern that was sent to the
                        ; PPU for the new bitplane

 LDA nameBufferHiAddr,X ; Set the high byte of the nametable buffer for the new
 STA nameBufferHi       ; bitplane in nameBufferHiAddr

 LDA #0                 ; Set the low byte of pattBufferAddr(1 0) to zero (we
 STA pattBufferAddr     ; will set the high byte in SetPatternBuffer below

 STA drawingPlaneDebug  ; Set drawingPlaneDebug = 0 (though this value is never
                        ; read, so this has no effect)

                        ; Fall through into SetPatternBuffer to set the high
                        ; bytes of the patten buffer address variables