From b60727508972da0925a73a9ad6960ca0c651232f Mon Sep 17 00:00:00 2001
From: Lucas Scharenbroich <lscharen@prowestgis.com>
Date: Sat, 20 Nov 2021 12:16:03 -0600
Subject: [PATCH] Separate updating a sprite's position with updating it's
 flags

---
 demos/sprites/App.Main.s | 20 +++++++++++++++++--
 src/GTE.s                |  3 ++-
 src/Sprite.s             | 43 +++++++++++++++++++++++++++++++++++-----
 src/Sprite2.s            |  2 +-
 4 files changed, 59 insertions(+), 9 deletions(-)

diff --git a/demos/sprites/App.Main.s b/demos/sprites/App.Main.s
index 8331e92..3fb9747 100644
--- a/demos/sprites/App.Main.s
+++ b/demos/sprites/App.Main.s
@@ -108,9 +108,10 @@ DoLoadBG1
                     stz        PlayerYVel
 
 ; Add a sprite to the engine and save it's sprite ID
+SPRITE_ID           equ        {SPRITE_16X16+145}
 
                     jsr        UpdatePlayerLocal
-                    lda        #$1800+145              ; 16x16 sprite, tile ID = 64
+                    lda        #SPRITE_ID              ; 16x16 sprite, tile ID = 145
                     ldx        PlayerX
                     ldy        PlayerY
                     jsl        AddSprite
@@ -240,7 +241,7 @@ EvtLoop
                     lda        PlayerID
                     ldx        PlayerX
                     ldy        PlayerY
-                    jsl        UpdateSprite           ; Move the sprite to this local position
+                    jsl        MoveSprite             ; Move the sprite to this local position
 
 ; Update the timers
                     jsl        DoTimers
@@ -408,6 +409,8 @@ UpdatePlayerLocal
 ; Simple updates with gravity and collisions.  It's important that eveything in this
 ; subroutine be done against 
 UpdatePlayerPos
+            stz  tmp0                        ; build up some flags
+
             stz  PlayerStanding
             lda  PlayerYVel
             bmi  :no_ground_check
@@ -454,16 +457,20 @@ UpdatePlayerPos
             lda  MaxGlobalX
             sta  PlayerGlobalX
 
+            ldx  #0
             lda  PlayerXVel
             beq  :no_dxv
             bpl  :pos_dxv
+            ldx  #SPRITE_HFLIP
             inc
             bra  :no_dxv
 :pos_dxv
             dec
 :no_dxv
             sta  PlayerXVel
+            stx  tmp0
 
+            ldx  #0
             lda  PlayerStanding
             bne  :too_fast
 
@@ -473,8 +480,17 @@ UpdatePlayerPos
             cmp  #4
             bcs  :too_fast
 :is_neg
+            ldx  #SPRITE_VFLIP
             sta  PlayerYVel
 :too_fast
+
+            txa
+            ora  tmp0
+            ora  #SPRITE_ID
+            tax
+            lda  PlayerID
+            jsl  UpdateSprite                          ; Change the tile ID and / or flags
+
             rts
 
 ; X = coordinate
diff --git a/src/GTE.s b/src/GTE.s
index d911db8..e223b7d 100644
--- a/src/GTE.s
+++ b/src/GTE.s
@@ -46,7 +46,8 @@ StopScript         EXT
 
 ; Sprite functions
 AddSprite          EXT
-UpdateSprite       EXT
+MoveSprite         EXT    ; Set an existing sprite's position
+UpdateSprite       EXT    ; Change an existing sprite's flags
 
 ; Direct access to internals
 DoScriptSeq        EXT
diff --git a/src/Sprite.s b/src/Sprite.s
index 5354a32..cd5cf5e 100644
--- a/src/Sprite.s
+++ b/src/Sprite.s
@@ -884,12 +884,11 @@ _GetSpriteVBuffAddr
             pla
             rts
 
-; Move a sprite to a new location.  If the tile ID of the sprite needs to be changed, then
-; a full remove/add cycle needs to happen
+; Update the sprite's flags. We do not allow the size fo a sprite to be changed.  That required
+; the sprite to be removed and re-added.
 ;
-; A = sprite ID
-; X = x position
-; Y = y position
+; A = Sprite ID
+; X = Sprite Tile ID and Flags
 UpdateSprite ENT
             phb
             phk
@@ -898,11 +897,45 @@ UpdateSprite ENT
             plb
             rtl
 
+
 _UpdateSprite
             cmp   #MAX_SPRITES*2                ; Make sure we're in bounds
             bcc   :ok
             rts
 
+:ok
+            stx   tmp0                          ; Save the horizontal position
+            and   #$FFFE                        ; Defensive
+            tax                                 ; Get the sprite index
+
+            lda   #SPRITE_STATUS_DIRTY          ; Content is changing, mark as dirty
+            sta   _Sprites+SPRITE_STATUS,x
+
+            lda   tmp0                          ; Update the Tile ID
+            sta   _Sprites+SPRITE_ID,x          ; Keep a copy of the full descriptor
+            jsr   _GetTileAddr                  ; This applies the TILE_ID_MASK
+            sta   _Sprites+TILE_DATA_OFFSET,x
+            rts
+
+; Move a sprite to a new location.  If the tile ID of the sprite needs to be changed, then
+; a full remove/add cycle needs to happen
+;
+; A = sprite ID
+; X = x position
+; Y = y position
+MoveSprite  ENT
+            phb
+            phk
+            plb
+            jsr    _MoveSprite
+            plb
+            rtl
+
+_MoveSprite
+            cmp   #MAX_SPRITES*2                ; Make sure we're in bounds
+            bcc   :ok
+            rts
+
 :ok
             stx   tmp0                          ; Save the horizontal position
             and   #$FFFE                        ; Defensive
diff --git a/src/Sprite2.s b/src/Sprite2.s
index 549471e..63fc8bd 100644
--- a/src/Sprite2.s
+++ b/src/Sprite2.s
@@ -25,7 +25,7 @@ _MarkDirtySprite
 ; Clip the sprite's extent to the screen so we can assume (mostly) position values from here on out.  Note that
 ; the sprite width and height are _only_ used in the clip and afterward all calculation use the clip rect
 ;
-; OPTIMIZATION NODE: These values can be calculated in AddSprite/UpdateSprite once and stored in the sprite
+; OPTIMIZATION NODE: These values can be calculated in AddSprite/MoveSprite once and stored in the sprite
 ;                    record since the screen size doesn't change.
 
         lda   _Sprites+SPRITE_ID,x               ; Get an index into the height/width tables based on the sprite bits