faster oam reset

Author: zohassadar

src/gamemodestate/pause.asm

@@ -38,10 +38,7 @@ pause:
 
 @pauseSetupPart2:
         jsr updateAudioAndWaitForNmi
-        lda #$FF
-        ldx #$02
-        ldy #$02
-        jsr memset_page
+        jsr resetOAMStaging
 
 @pauseLoop:
         lda qualFlag

src/util/core.asm

@@ -50,6 +50,23 @@ random10:
         bpl random10
         rts
 
+resetOAMStaging:
+; Hide a sprite by moving it down offscreen, by writing any values between #$EF-#$FF here. 
+; Sprites are never displayed on the first line of the picture, and it is impossible to place 
+; a sprite partially off the top of the screen. 
+; https://www.nesdev.org/wiki/PPU_OAM
+        ldx #$00
+        lda #$FF
+@hideY:
+        sta oamStaging,x
+        inx
+        inx
+        inx
+        inx
+        bne @hideY
+        rts
+
+
 ; canon is waitForVerticalBlankingInterval
 updateAudioWaitForNmiAndResetOamStaging:
         jsr updateAudio_jmp
@@ -59,10 +76,7 @@ updateAudioWaitForNmiAndResetOamStaging:
 @checkForNmi:
         lda verticalBlankingInterval
         beq @checkForNmi
-        lda #$FF
-        ldx #$02
-        ldy #$02
-        jsr memset_page
+        jsr resetOAMStaging
         rts
 
 updateAudioAndWaitForNmi: