Drawing the screen: UpdateView

       Name: UpdateView                                              [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Update the view
  Deep dive: Views and view types in NES Elite
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * BRIEF2 calls UpdateView
             * BuyAndSellCargo calls UpdateView
             * EQSHP calls UpdateView
             * TBRIEF calls UpdateView
             * TT22 calls UpdateView
             * TT23 calls UpdateView
             * TT25 calls UpdateView
             * UpdateView_b0 calls UpdateView


.UpdateView

 LDA firstFreePattern   ; If firstFreePattern = 0, set firstFreePattern = 255
 BNE upvw1              ;
 LDA #255               ; This ensures that the call to CopyNameBuffer0To1 below
 STA firstFreePattern   ; tells the NMI handler to send pattern entries up to
                        ; the first free pattern, or to send patterns up to the
                        ; very end if we have run out of free patterns (in which
                        ; case firstFreePattern was zero)

.upvw1

 LDA #0                 ; Tell the NMI handler to send nametable entries from
 STA firstNameTile      ; tile 0 onwards

 LDA #108               ; Tell the NMI handler to only clear nametable entries
 STA maxNameTileToClear ; up to tile 108 * 8 = 864 (i.e. up to the end of tile
                        ; row 26)

 STA lastNameTile       ; Tell the PPU to send nametable entries up to tile
 STA lastNameTile+1     ; 108 * 8 = 864 (i.e. to the end of tile row 26) in both
                        ; bitplanes

 LDX #37                ; Set X = 37 to use as the first pattern for when there
                        ; is an icon bar

 LDA QQ11               ; If bit 6 of the view type is clear, then there is an
 AND #%01000000         ; icon bar, so jump to upvw2 to skip the following
 BEQ upvw2              ; instruction

 LDX #4                 ; Set X = 4 to use as the first pattern for when there
                        ; is no icon bar

.upvw2

 STX firstPattern       ; Tell the NMI handler to send pattern entries from
                        ; pattern X in the buffer (i.e. from pattern 4 if there
                        ; is no icon bar, or from pattern 37 if there is an
                        ; icon bar)

 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

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

 LDA QQ11               ; If the new view in QQ11 is the same as the old view in
 CMP QQ11a              ; QQ11a, then jump to upvw6 to call UpdateScreen before
 BEQ upvw6              ; jumping back to upvw3 (which will either call
                        ; SendViewToPPU to update the view straight away, if
                        ; it's been faded to black, otherwise it will call
                        ; SetupFullViewInNMI to update the view in VBlank, to
                        ; prevent screen corruption)

 JSR SendViewToPPU_b3   ; Otherwise the view is changing, so it has already been
                        ; faded out and we can call SendViewToPPU to update the
                        ; view straight away without caring about screen
                        ; corruption

.upvw3

 LDX #$FF               ; Set X = $FF to use as the value of showIconBarPointer
                        ; below (i.e. show the icon bar pointer)

 LDA QQ11               ; If the view type in QQ11 is $95 (Trumble mission
 CMP #$95               ; briefing), jump to upvw4 to set showIconBarPointer to
 BEQ upvw4              ; 0 (i.e. hide the icon bar pointer)

 CMP #$DF               ; If the view type in QQ11 is $DF (Start screen with
 BEQ upvw4              ; the normal font loaded), jump to upvw4 to set
                        ; showIconBarPointer to 0 (i.e. hide the icon bar
                        ; pointer)

 CMP #$92               ; If the view type in QQ11 is $92 (Mission 1 rotating
 BEQ upvw4              ; ship briefing), jump to upvw4 to set
                        ; showIconBarPointer to 0 (i.e. hide the icon bar
                        ; pointer)

 CMP #$93               ; If the view type in QQ11 is $93 (Mission 1 text
 BEQ upvw4              ; briefing), jump to upvw4 to set showIconBarPointer
                        ; to 0 (i.e. hide the icon bar pointer)

 ASL A                  ; If bit 6 of the view type in QQ11 is clear, then there
 BPL upvw5              ; is an icon bar, so jump to upvw5 to set
                        ; showIconBarPointer to $FF (i.e. show the icon bar
                        ; pointer)

.upvw4

 LDX #0                 ; Set X = 0 to use as the value of showIconBarPointer
                        ; below (i.e. hide the icon bar pointer)

.upvw5

 STX showIconBarPointer ; Set showIconBarPointer to X, so we set it as follows:
                        ;
                        ;   * 0 if the view is a mission briefing, or the Start
                        ;     screen with the normal font loaded, or has no
                        ;     icon bar (in which case we hide the icon bar
                        ;     pointer)
                        ;
                        ;   * $FF otherwise (in which case we show 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

 RTS                    ; Return from the subroutine

.upvw6

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

 JMP upvw3              ; Jump back to upvw3 to continue updating the view