Skip to navigation

⌂ ∞ ▽ Elite on the 6502

Drawing the screen: DrawBoxEdges

[NES version, Bank 7]

       Name: DrawBoxEdges                                            [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Draw the left and right edges of the box along the sides of the
             screen, drawing into the nametable buffer for the drawing bitplane

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawScreenInNMI calls DrawBoxEdges
             * SetDrawPlaneFlags calls DrawBoxEdges
             * UpdateView calls DrawBoxEdges




.DrawBoxEdges

 LDX drawingBitplane    ; If the drawing bitplane is set to 1, jump to boxe1 to
 BNE boxe1              ; draw the box edges in bitplane 1

                        ; Otherwise we draw the box edges in bitplane 0

 LDA boxEdge1           ; Set A to the tile number for the left edge of the box,
                        ; which will either be tile 1 for the normal view (a
                        ; three-pixel wide vertical bar along the right edge of
                        ; the tile), or tile 0 (blank) for the death screen

 STA nameBuffer0+1      ; Write this tile into column 1 on rows 0 to 19 in
 STA nameBuffer0+1*32+1 ; nametable buffer 0 to draw the left edge of the box
 STA nameBuffer0+2*32+1 ; (column 1 is the left edge because the screen is
 STA nameBuffer0+3*32+1 ; scrolled horizontally by one block)
 STA nameBuffer0+4*32+1
 STA nameBuffer0+5*32+1
 STA nameBuffer0+6*32+1
 STA nameBuffer0+7*32+1
 STA nameBuffer0+8*32+1
 STA nameBuffer0+9*32+1
 STA nameBuffer0+10*32+1
 STA nameBuffer0+11*32+1
 STA nameBuffer0+12*32+1
 STA nameBuffer0+13*32+1
 STA nameBuffer0+14*32+1
 STA nameBuffer0+15*32+1
 STA nameBuffer0+16*32+1
 STA nameBuffer0+17*32+1
 STA nameBuffer0+18*32+1
 STA nameBuffer0+19*32+1

 LDA boxEdge2           ; Set A to the tile number for the right edge of the
                        ; box, which will either be tile 2 for the normal view
                        ; (a three-pixel wide vertical bar along the left edge
                        ; of the tile), or tile 0 (blank) for the death screen

 STA nameBuffer0        ; Write this tile into column 0 on rows 0 to 19 in
 STA nameBuffer0+1*32   ; nametable buffer 0 to draw the right edge of the box
 STA nameBuffer0+2*32   ; (column 0 is the right edge because the screen is
 STA nameBuffer0+3*32   ; scrolled horizontally by one block)
 STA nameBuffer0+4*32
 STA nameBuffer0+5*32
 STA nameBuffer0+6*32
 STA nameBuffer0+7*32
 STA nameBuffer0+8*32
 STA nameBuffer0+9*32
 STA nameBuffer0+10*32
 STA nameBuffer0+11*32
 STA nameBuffer0+12*32
 STA nameBuffer0+13*32
 STA nameBuffer0+14*32
 STA nameBuffer0+15*32
 STA nameBuffer0+16*32
 STA nameBuffer0+17*32
 STA nameBuffer0+18*32
 STA nameBuffer0+19*32

 RTS                    ; Return from the subroutine

.boxe1

 LDA boxEdge1           ; Set A to the tile number for the left edge of the box,
                        ; which will either be tile 1 for the normal view (a
                        ; three-pixel wide vertical bar along the right edge of
                        ; the tile), or tile 0 (blank) for the death screen

 STA nameBuffer1+1      ; Write this tile into column 1 on rows 0 to 19 in
 STA nameBuffer1+1*32+1 ; nametable buffer 1 to draw the left edge of the box
 STA nameBuffer1+2*32+1 ; (column 1 is the left edge because the screen is
 STA nameBuffer1+3*32+1 ; scrolled horizontally by one block)
 STA nameBuffer1+4*32+1
 STA nameBuffer1+5*32+1
 STA nameBuffer1+6*32+1
 STA nameBuffer1+7*32+1
 STA nameBuffer1+8*32+1
 STA nameBuffer1+9*32+1
 STA nameBuffer1+10*32+1
 STA nameBuffer1+11*32+1
 STA nameBuffer1+12*32+1
 STA nameBuffer1+13*32+1
 STA nameBuffer1+14*32+1
 STA nameBuffer1+15*32+1
 STA nameBuffer1+16*32+1
 STA nameBuffer1+17*32+1
 STA nameBuffer1+18*32+1
 STA nameBuffer1+19*32+1

 LDA boxEdge2           ; Set A to the tile number for the right edge of the
                        ; box, which will either be tile 2 for the normal view
                        ; (a three-pixel wide vertical bar along the left edge
                        ; of the tile), or tile 0 (blank) for the death screen

 STA nameBuffer1        ; Write this tile into column 0 on rows 0 to 19 in
 STA nameBuffer1+1*32   ; nametable buffer 1 to draw the right edge of the box
 STA nameBuffer1+2*32   ; (column 0 is the right edge because the screen is
 STA nameBuffer1+3*32   ; scrolled horizontally by one block)
 STA nameBuffer1+4*32
 STA nameBuffer1+5*32
 STA nameBuffer1+6*32
 STA nameBuffer1+7*32
 STA nameBuffer1+8*32
 STA nameBuffer1+9*32
 STA nameBuffer1+10*32
 STA nameBuffer1+11*32
 STA nameBuffer1+12*32
 STA nameBuffer1+13*32
 STA nameBuffer1+14*32
 STA nameBuffer1+15*32
 STA nameBuffer1+16*32
 STA nameBuffer1+17*32
 STA nameBuffer1+18*32
 STA nameBuffer1+19*32

 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 RTS                    ; Return from the subroutine