First public commit.

lenser/bbc/viewer/assemble.py

@@ -0,0 +1,102 @@
+"""Assemble the BBC 6502 viewer with `xa` and patch in per-image parameters."""
+
+from __future__ import annotations
+
+import os
+import shutil
+import subprocess
+import tempfile
+
+VIEWER_DIR = os.path.dirname(os.path.abspath(__file__))
+LOAD_ADDR = 0x1900               # DFS PAGE
+WAIT_MODES = {"forever": 0, "key": 1, "seconds": 2}
+
+
+class AssemblerError(RuntimeError):
+    pass
+
+
+def have_xa() -> bool:
+    return shutil.which("xa") is not None
+
+
+def _xa(wrapper: str) -> bytes:
+    if not have_xa():
+        raise AssemblerError("The 'xa' (xa65) assembler was not found on PATH.\n"
+                             "Install it with:  sudo apt install xa65")
+    with tempfile.TemporaryDirectory() as td:
+        out = os.path.join(td, "v.bin")
+        fd, wrap = tempfile.mkstemp(suffix=".s", prefix="_wrap_", dir=VIEWER_DIR)
+        try:
+            with os.fdopen(fd, "w") as f:
+                f.write(wrapper)
+            proc = subprocess.run(["xa", "-o", out, os.path.basename(wrap)],
+                                  capture_output=True, text=True, cwd=VIEWER_DIR)
+            if proc.returncode != 0:
+                raise AssemblerError(f"xa failed:\n{proc.stdout}{proc.stderr}")
+            with open(out, "rb") as f:
+                return f.read()
+        finally:
+            os.unlink(wrap)
+
+
+SS_WAITMODE = {"key": 1, "seconds": 2, "both": 3}
+
+
+def build_slideshow_viewer(bbc_mode: int, ncol: int, base: int, palettes,
+                           advance: str = "both", seconds: int = 10,
+                           loop: bool = True, video: str = "pal") -> bytes:
+    """Return the multi-image BBC loader (origin $1900).
+
+    ``palettes`` is one physical-colour list per image (each truncated/padded to
+    ncol) -- emitted as the ss_pal table the loader indexes by slide; the screen
+    base hex is patched into the OSCLI *LOAD string.
+    """
+    if not palettes:
+        raise AssemblerError("a slideshow needs at least one image")
+    rate = 60 if video == "ntsc" else 50
+    flat = []
+    for p in palettes:
+        row = list(p[:ncol])
+        flat += row + [0] * (ncol - len(row))
+    table = ",".join(str(b & 0xFF) for b in flat)
+    wrapper = (f"#define WAITMODE {SS_WAITMODE[advance]}\n"
+               f"#define WAITSECS {max(0, int(seconds))}\n"
+               f"#define RATE {rate}\n"
+               f"#define NIMAGES {len(palettes)}\n"
+               f"#define LOOPFLAG {1 if loop else 0}\n"
+               f"#define MODE {bbc_mode}\n"
+               f"#define NCOL {ncol}\n"
+               '#include "slideshow.s"\n'
+               "ss_pal:\n"
+               f"        .byte {table}\n")
+    raw = bytearray(_xa(wrapper))
+    off = raw.find(b"LOAD 00 ")
+    if off < 0:
+        raise AssemblerError("could not locate the OSCLI string to patch")
+    raw[off + 8:off + 12] = f"{base:04X}".encode("ascii")   # screen-base hex
+    return bytes(raw)
+
+
+def build_viewer(bbc_mode: int, ncol: int, physicals, base: int,
+                 display: str = "forever", seconds: int = 0,
+                 video: str = "pal") -> bytes:
+    """Return the assembled loader (origin $1900) with the mode/palette/screen-base
+    parameters patched in."""
+    waitmode = WAIT_MODES.get(display, 0)
+    rate = 60 if video == "ntsc" else 50         # bbcb is PAL (50 Hz)
+    wrapper = (f"#define WAITMODE {waitmode}\n"
+               f"#define WAITSECS {max(0, int(seconds))}\n"
+               f"#define RATE {rate}\n"
+               '#include "bbc.s"\n')
+    raw = bytearray(_xa(wrapper))
+
+    off = raw.find(b"LOAD IMG ")
+    if off < 0:
+        raise AssemblerError("could not locate the OSCLI string to patch")
+    raw[off + 9:off + 13] = f"{base:04X}".encode("ascii")   # screen-base hex
+    raw[off + 14] = bbc_mode & 0xFF                          # p_mode
+    raw[off + 15] = ncol & 0xFF                              # p_ncol
+    for i, p in enumerate(physicals[:8]):                    # p_pal
+        raw[off + 16 + i] = p & 0xFF
+    return bytes(raw)