The FlipDrawingPlane (Bank 7) subroutine - Elite on the BBC Micro and NES

       Name: FlipDrawingPlane                                        [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Flip the drawing bitplane
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DEATH calls FlipDrawingPlane
             * DrawScrollFrames calls FlipDrawingPlane
             * DrawShipInBitplane calls FlipDrawingPlane
             * LAUN calls FlipDrawingPlane
             * LL164 calls FlipDrawingPlane
             * Main flight loop (Part 1 of 16) calls FlipDrawingPlane
             * RunDemoFlightLoop calls FlipDrawingPlane


.FlipDrawingPlane

 LDA drawingBitplane    ; Set X to the opposite bitplane to the current drawing
 EOR #1                 ; bitplane
 TAX

 JSR SetDrawingBitplane ; Set X as the new drawing bitplane, so this effectively
                        ; flips the drawing bitplane between 0 and 1

 JMP ClearDrawingPlane  ; Jump to ClearDrawingPlane to clear the buffers for the
                        ; new drawing bitplane, returning from the subroutine
                        ; using a tail call

[X]

Subroutine ClearDrawingPlane (Part 1 of 3) (category: Drawing the screen)

Clear the nametable and pattern buffers for the newly flipped drawing plane

[X]

Subroutine SetDrawingBitplane (category: Drawing the screen)

Set the drawing bitplane to a specified value

[X]

Variable drawingBitplane in workspace ZP

Flipped manually by calling FlipDrawingPlane, controls whether we are showing nametable/palette buffer 0 or 1

Drawing the screen: FlipDrawingPlane

[NES version, Bank 7]