Stardust: ResetStardust

       Name: ResetStardust                                           [Show more]
       Type: Subroutine
   Category: Stardust
    Summary: Hide the sprites for the stardust
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * SendSpaceViewToPPU calls ResetStardust


.ResetStardust

 LDX #NOST              ; Set X to the maximum number of stardust particles, so
                        ; we loop through all the particles of stardust in the
                        ; following, hiding them all

 LDY #152               ; Set Y to the starting index in the sprite buffer, so
                        ; we start hiding from sprite 152 / 4 = 38 (as each
                        ; sprite in the buffer consists of four bytes)

.rest1

 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

 LDA #240               ; Set A to the y-coordinate that's just below the bottom
                        ; of the screen, so we can hide the required sprites by
                        ; moving them off-screen

 STA ySprite0,Y         ; Set the y-coordinate for sprite Y / 4 to 240 to hide
                        ; it (the division by four is because each sprite in the
                        ; sprite buffer has four bytes of data)

 LDA #210               ; Set the sprite to use pattern number 210 for the
 STA pattSprite0,Y      ; largest particle of stardust (the stardust particle
                        ; patterns run from pattern 210 to 214, decreasing in
                        ; size as the number increases)

 TXA                    ; Take the particle number, which is between 1 and 20
 LSR A                  ; (as NOST is 20), and rotate it around from %76543210
 ROR A                  ; to %10xxxxx3 (where x indicates a zero), storing the
 ROR A                  ; result as the sprite attribute
 AND #%11100001         ;
 STA attrSprite0,Y      ; This sets the flip horizontally and flip vertically
                        ; attributes to bits 0 and 1 of the particle number, and
                        ; the palette to bit 3 of the particle number, so the
                        ; reset stardust particles have a variety of reflections
                        ; and palettes

 INY                    ; Add 4 to Y so it points to the next sprite's data in
 INY                    ; the sprite buffer
 INY
 INY

 DEX                    ; Decrement the loop counter in X

 BNE rest1              ; Loop back until we have hidden X sprites

 JSR WaitForNMI         ; Wait until the next NMI interrupt has passed (i.e. the
                        ; next VBlank)

 JSR SIGHT_b3           ; Draw the laser crosshairs

                        ; Fall through into SetupSpaceView to finish setting up
                        ; the space view's NMI configuration