first draft of an unpack wrapper, we probably want to use VolRegion or similar

examples/hello.rs

@@ -1,7 +1,7 @@
 #![no_std]
 #![no_main]
 
-use core::{fmt::Write, mem::size_of_val};
+use core::fmt::Write;
 use gba::{
   mgba::{MgbaBufferedLogger, MgbaMessageLevel},
   prelude::*,
@@ -63,15 +63,7 @@ extern "C" fn main() -> ! {
 
   {
     // get our tile data into memory.
-    let src = CGA_8X8_THICK.as_ptr().cast::<u8>();
+    Cga8x8Thick.bitunpack_to_4bpp(CHARBLOCK0_4BPP, 0);
-    let dest = CHARBLOCK0_4BPP.index(0).as_usize() as *mut u32;
-    let info = BitUnpackInfo {
-      src_byte_len: size_of_val(&CGA_8X8_THICK) as u16,
-      src_elem_width: 1,
-      dest_elem_width: 4,
-      offset_and_touch_zero: 0,
-    };
-    unsafe { BitUnPack(src, dest, &info) };
   }
 
   {

src/builtin_art/cga_8x8_thick.rs

@@ -1,3 +1,12 @@
+use core::mem::size_of_val;
+
+use voladdress::{Safe, VolBlock};
+
+use crate::{
+  bios::{BitUnPack, BitUnpackInfo},
+  video::Tile4,
+};
+
 /// The CGA [Code Page 437][cp437] type face, with thick lines.
 ///
 /// There's 256 tiles, packed down to 1bpp. To decompress this into 4bpp tile
@@ -131,3 +140,23 @@ pub static CGA_8X8_THICK: [u32; 512] = [
   0x3636361E, 0x00000036, 0x060C180E, 0x0000001E, 0x3C3C0000, 0x00003C3C,
   0x00000000, 0x00000000,
 ];
+
+#[derive(Debug, Clone, Copy)]
+pub struct Cga8x8Thick;
+
+impl Cga8x8Thick {
+  #[inline]
+  pub fn bitunpack_to_4bpp(
+    self, b: VolBlock<Tile4, Safe, Safe, 512>, offset_and_touch_zero: u32,
+  ) {
+    let src = CGA_8X8_THICK.as_ptr();
+    let dest = b.index(0).as_usize() as *mut u32;
+    let info = BitUnpackInfo {
+      src_byte_len: size_of_val(&CGA_8X8_THICK) as u16,
+      src_elem_width: 1,
+      dest_elem_width: 4,
+      offset_and_touch_zero,
+    };
+    unsafe { BitUnPack(src.cast(), dest, &info) };
+  }
+}