added cx16 sprite demo

examples/cx16/bobs.p8

@@ -5,7 +5,7 @@
 
 ; "unlimited sprites / bobs" demo effect.
 ; Note that everything is prog8, no inline assembly used/required.
-
+; Note2: these aren't actual sprites, it's a bitmap backbuffer display trick.
 
 main {
     sub start() {
@@ -104,7 +104,7 @@ main {
 
         bitshift(lsb(blit_x) & 7)
 
-        ; left column of the (shifted)sprite
+        ; left column of the (shifted) "sprite" (bob)
         cx16.VERA_CTRL = 0
         cx16.VERA_ADDR_L = lsb(vmem)
         cx16.VERA_ADDR_M = msb(vmem)
@@ -117,7 +117,7 @@ main {
         for ix in 0 to len(shifted_sprite)-1 step 3
             cx16.VERA_DATA1 = cx16.VERA_DATA0 & shifted_mask[ix] | shifted_sprite[ix]
 
-        ; middle column of the (shifted)sprite
+        ; middle column of the (shifted) "sprite" (bob)
         vmem++
         cx16.VERA_CTRL = 0
         cx16.VERA_ADDR_L = lsb(vmem)
@@ -128,7 +128,7 @@ main {
         for ix in 1 to len(shifted_sprite)-1 step 3
             cx16.VERA_DATA1 = cx16.VERA_DATA0 & shifted_mask[ix] | shifted_sprite[ix]
 
-        ; right column of the (shifted)sprite
+        ; right column of the (shifted) "sprite" (bob)
         vmem++
         cx16.VERA_CTRL = 0
         cx16.VERA_ADDR_L = lsb(vmem)

examples/cx16/sprites/convertsprite.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+from PIL import Image
+
+def make_cx16_palette(palette: list[int]) -> bytes:
+    cx16palette = bytearray()
+    for pi in range(0, len(palette), 3):
+        r, g, b = palette[pi] >> 4, palette[pi + 1] >> 4, palette[pi + 2] >> 4
+        cx16palette.append(g << 4 | b)
+        cx16palette.append(r)
+    return cx16palette
+
+
+img = Image.open("dragonsprite.png")
+assert img.size == (64, 128) and img.mode == 'P'
+
+data = bytearray()
+for y in range(0, 128):
+    for x in range(0, 64, 2):
+        pix1 = img.getpixel((x, y))
+        pix2 = img.getpixel((x + 1, y))
+        data.append(pix1 << 4 | pix2)
+
+palette = make_cx16_palette(img.getpalette())
+
+assert len(data) == 64 * 128 / 2
+assert len(palette) <= 16*2
+open("DRAGONSPRITE.PAL", "wb").write(palette)
+open("DRAGONSPRITE.BIN", "wb").write(data)

examples/cx16/sprites/dragon.p8

@@ -0,0 +1,76 @@
+%import diskio
+%zeropage basicsafe
+%option no_sysinit
+
+main {
+    const ubyte SPRITE_BANK = 0
+    const uword SPRITE_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
+
+        word xpos = -64
+        word ypos = 100
+        ubyte tt = 0
+        bool flipped
+
+        repeat {
+            if flipped
+                xpos -= 2
+            else
+                xpos += 2
+
+            if xpos >= 640 or xpos <= -64
+                flipped = not flipped
+
+            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 {
+    ; sprite registers base in VRAM:  $1fc00
+    ;        Sprite 0:          $1FC00 - $1FC07     ; used by the kernal for mouse pointer
+    ;        Sprite 1:          $1FC08 - $1FC0F
+    ;        Sprite 2:          $1FC10 - $1FC17
+    ;        …
+    ;        Sprite 127:        $1FFF8 - $1FFFF
+    const uword VERA_SPRITEREGS = $fc00     ; $1fc00
+    const ubyte PALETTE_OFFSET = 32         ; in bytes, so 16 color entries
+
+    uword sprite_regs
+
+    sub init(ubyte sprite_num, uword data_addr) {
+        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)
+    }
+
+    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)
+    }
+
+    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))
+    }
+}