The ChangeToView (Bank 0) subroutine - Elite on the BBC Micro and NES

       Name: ChangeToView                                            [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Clear the screen and set a new view type
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BRIEF calls ChangeToView
             * ChangeToView_b0 calls ChangeToView
             * LAUN calls ChangeToView
             * TITLE calls ChangeToView


 Arguments:

   A                    The type of the new view


.ChangeToView

 JSR TT66               ; Clear the screen and set the view type in QQ11 to the
                        ; value of A

 JSR CopyNameBuffer0To1 ; Copy the contents of nametable buffer 0 to nametable
                        ; buffer

 JSR UpdateScreen       ; Update the screen by sending data to the PPU, either
                        ; immediately or during VBlank, depending on whether
                        ; the screen is visible

 LDA #$00               ; Set the view type in QQ11 to $00 (Space view with no
 STA QQ11               ; font loaded)

 STA QQ11a              ; Set the old view type in QQ11a to $00 (Space view with
                        ; no fonts loaded)

 STA showIconBarPointer ; Set showIconBarPointer to 0 to indicate that we should
                        ; hide the icon bar pointer

 LDA firstFreePattern   ; Tell the NMI handler to send pattern entries from the
 STA firstPattern       ; first free pattern onwards, so we don't waste time
                        ; resending the static patterns we have already sent

 LDA #80                ; Tell the NMI handler to only clear nametable entries
 STA maxNameTileToClear ; up to tile 80 * 8 = 640 (i.e. up to the end of tile
                        ; row 19)

 LDX #8                 ; Tell the NMI handler to send nametable entries from
 STX firstNameTile      ; tile 8 * 8 = 64 onwards (i.e. from the start of tile
                        ; row 2)

 RTS                    ; Return from the subroutine

[X]

Subroutine CopyNameBuffer0To1 (category: Drawing the screen)

Copy the contents of nametable buffer 0 to nametable buffer 1

[X]

Variable QQ11 in workspace ZP

This contains the type of the current view (or, if we are changing views, the type of the view we are changing to)

[X]

Variable QQ11a in workspace ZP

Contains the old view type when changing views

[X]

Subroutine TT66 (category: Drawing the screen)

Clear the screen and set the new view type

[X]

Subroutine UpdateScreen (category: PPU)

Update the screen by sending data to the PPU, either immediately or during VBlank, depending on whether the screen is visible

[X]

Variable firstFreePattern in workspace ZP

Contains the number of the first free pattern in the pattern buffer that we can draw into next (or 0 if there are no free patterns)

[X]

Variable firstNameTile in workspace ZP

The number of the first tile for which we send nametable data to the PPU in the NMI handler (potentially for both bitplanes, if both are configured to be sent)

[X]

Variable firstPattern in workspace ZP

The number of the first pattern for which we send data to the PPU in the NMI handler (potentially for both bitplanes, if both are configured to be sent)

[X]

Variable maxNameTileToClear in workspace ZP

The tile number at which the NMI handler should stop clearing tiles in the nametable buffers during its clearing cycle

[X]

Variable showIconBarPointer in workspace WP

Controls whether to show the icon bar pointer

Drawing the screen: ChangeToView

[NES version, Bank 0]