From 83d459252641377a6cdaffbdfee8707d20f15938 Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Thu, 31 Aug 2023 22:31:04 +0200
Subject: [PATCH] tweaks to the cx16 sprite example

---
 examples/cx16/sprites/dragon.p8 | 66 +++++++++++++++++++--------------
 1 file changed, 38 insertions(+), 28 deletions(-)

diff --git a/examples/cx16/sprites/dragon.p8 b/examples/cx16/sprites/dragon.p8
index 1cdebadc2..06938e083 100644
--- a/examples/cx16/sprites/dragon.p8
+++ b/examples/cx16/sprites/dragon.p8
@@ -3,37 +3,39 @@
 %option no_sysinit
 
 main {
-    const ubyte SPRITE_BANK = 0
-    const uword SPRITE_ADDR = $2000
+    ; we choose arbitrary unused vram location for sprite data: $12000
+    const ubyte SPRITE_DATA_BANK = 1
+    const uword SPRITE_DATA_ADDR = $2000
 
 
     sub start() {
-        void diskio.vload_raw("dragonsprite.bin", SPRITE_BANK, SPRITE_ADDR)
-        void diskio.vload_raw("dragonsprite.pal", 1, $fa00 + sprites.PALETTE_OFFSET)    ; load directly into vera color palette
-        sprites.init(1, SPRITE_ADDR)                ; top half of dragon
-        sprites.init(2, SPRITE_ADDR + 64*64/2)      ; bottom half of dragon
+        void diskio.vload_raw("dragonsprite.bin", SPRITE_DATA_BANK, SPRITE_DATA_ADDR)
+        void diskio.vload_raw("dragonsprite.pal", 1, $fa00 + sprites.PALETTE_OFFSET*2)    ; load directly into vera color palette
+        sprites.init(1, SPRITE_DATA_BANK, SPRITE_DATA_ADDR)                ; top half of dragon
+        sprites.init(2, SPRITE_DATA_BANK, SPRITE_DATA_ADDR + 64*64/2)      ; bottom half of dragon
 
         word xpos = -64
         word ypos = 100
         ubyte tt = 0
-        bool flipped
+        bool flippedx
 
         repeat {
-            if flipped
+            if flippedx
                 xpos -= 2
             else
                 xpos += 2
 
             if xpos >= 640 or xpos <= -64
-                flipped = not flipped
+                flippedx = not flippedx
 
             ypos = (240-64 as word) + math.sin8(tt)
             tt++
+
             sys.waitvsync()
             sprites.pos(1, xpos, ypos)
             sprites.pos(2, xpos, ypos+64)
-            sprites.flipx(1, flipped)
-            sprites.flipx(2, flipped)
+            sprites.flipx(1, flippedx)
+            sprites.flipx(2, flippedx)
         }
     }
 }
@@ -46,31 +48,39 @@ sprites {
     ;        …
     ;        Sprite 127:        $1FFF8 - $1FFFF
     const uword VERA_SPRITEREGS = $fc00     ; $1fc00
-    const ubyte PALETTE_OFFSET = 32         ; in bytes, so 16 color entries
+    const ubyte PALETTE_OFFSET = 16         ; color palette indices 16-31
 
-    uword sprite_regs
+    uword @zp sprite_reg
 
-    sub init(ubyte sprite_num, uword data_addr) {
+    sub init(ubyte sprite_num, ubyte data_bank, uword data_addr) {
+        hide(sprite_num)
         cx16.VERA_DC_VIDEO |= %01000000             ; enable sprites globally
-        uword address = data_addr >> 5
-        sprite_regs = VERA_SPRITEREGS + sprite_num*$0008
-        cx16.vpoke(1, sprite_regs, lsb(address))                    ; address 12:5
-        cx16.vpoke(1, sprite_regs+1, %00000000 | msb(address))      ; 4 bpp + address 16:13
-        cx16.vpoke(1, sprite_regs+6, %00001100)                     ; sprite flags: enable sprite, z depth %11 = before both layers
-        cx16.vpoke(1, sprite_regs+7, %11110000 | PALETTE_OFFSET>>5) ; 64x64 pixels, palette offset
-        pos(sprite_num, 100, 100)
+        data_addr >>= 5
+        data_addr |= (data_bank as uword)<<11
+        sprite_reg = VERA_SPRITEREGS + sprite_num*$0008
+        cx16.vpoke(1, sprite_reg, lsb(data_addr))                  ; address 12:5
+        cx16.vpoke(1, sprite_reg+1, %00000000 | msb(data_addr))    ; 4 bpp + address 16:13
+        cx16.vpoke(1, sprite_reg+6, %00001100)                     ; z depth %11 = in front of both layers, no flips
+        cx16.vpoke(1, sprite_reg+7, %11110000 | PALETTE_OFFSET>>4) ; 64x64 pixels, palette offset
+    }
+
+    sub hide(ubyte sprite_num) {
+        pos(sprite_num, -64, -64)
     }
 
     sub flipx(ubyte sprite_num, bool flipped) {
-        uword sprite_reg = VERA_SPRITEREGS + sprite_num*$0008 + 6
-        cx16.vpoke(1, sprite_reg, cx16.vpeek(1, sprite_reg) & %11111110 | flipped)
+        cx16.vpoke_mask(1, VERA_SPRITEREGS + 6 + sprite_num*$0008, %11111110, flipped)
+    }
+
+    sub flipy(ubyte sprite_num, bool flipped) {
+        cx16.vpoke_mask(1, VERA_SPRITEREGS + 6 + sprite_num*$0008, %11111101, flipped<<1)
     }
 
     sub pos(ubyte sprite_num, word x, word y) {
-        sprite_regs = VERA_SPRITEREGS + sprite_num*$0008
-        cx16.vpoke(1, sprite_regs+2, lsb(x))
-        cx16.vpoke(1, sprite_regs+3, msb(x))
-        cx16.vpoke(1, sprite_regs+4, lsb(y))
-        cx16.vpoke(1, sprite_regs+5, msb(y))
+        sprite_reg = VERA_SPRITEREGS + 2 + sprite_num*$0008
+        cx16.vpoke(1, sprite_reg, lsb(x))
+        cx16.vpoke(1, sprite_reg+1, msb(x))
+        cx16.vpoke(1, sprite_reg+2, lsb(y))
+        cx16.vpoke(1, sprite_reg+3, msb(y))
     }
 }