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⌂ ∞ ▽ Elite on the 6502

Drawing the screen: SetDrawPlaneFlags

[NES version, Bank 7]

       Name: SetDrawPlaneFlags                                       [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Set the drawing bitplane flags to the specified value, draw the
             box edges and set the next free tile number
  Deep dive: Drawing vector graphics using NES tiles

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DEATH calls SetDrawPlaneFlags
             * DrawSpaceViewInNMI calls SetDrawPlaneFlags
             * SendBitplaneToPPU calls SetDrawPlaneFlags
             * SetupViewInNMI calls SetDrawPlaneFlags




.SetDrawPlaneFlags

 PHA                    ; Store A on the stack, so we can retrieve them below
                        ; when setting the new drawing bitplane flags

 JSR DrawBoxEdges       ; Draw the left and right edges of the box along the
                        ; sides of the screen, drawing into the nametable buffer
                        ; for the drawing bitplane

 LDX drawingBitplane    ; Set X to the drawing bitplane

 LDA firstFreePattern   ; Tell the NMI handler to send pattern entries up to the
 STA lastPattern,X      ; first free pattern, for the drawing bitplane in X

 PLA                    ; Retrieve A from the stack and set it as the value of
 STA bitplaneFlags,X    ; the drawing bitplane flags

 RTS                    ; Return from the subroutine