First public commit.

lenser/coco3/convert/_common.py

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+"""Shared CoCo 3 GIME encoder helpers: global palette selection + linear packing.
+
+GIME native graphics modes have no per-cell colour limit: a flat palette of pens
+(16/4/2), each pen any of the 64 colours.  Pick the best N-colour sub-palette,
+dither to it, then pack pens into the LINEAR 80-byte x 192-row screen.
+"""
+from __future__ import annotations
+
+import numpy as np
+
+from ... import dither, palette as c64pal
+from .. import palette as g
+
+BYTES_PER_ROW, ROWS = 80, 192
+
+
+def choose_inks(img_lab, plab, n):
+    """Greedy forward selection of the ``n`` palette colours (0-63) minimising
+    nearest-colour error over the image."""
+    flat = img_lab.reshape(-1, 3)
+    d = np.sum((flat[:, None, :] - plab[None, :, :]) ** 2, axis=-1)
+    chosen, best = [], np.full(flat.shape[0], np.inf)
+    for _ in range(n):
+        cand = np.minimum(best[:, None], d).sum(0)
+        for c in chosen:
+            cand[c] = np.inf
+        c = int(cand.argmin())
+        chosen.append(c)
+        best = np.minimum(best, d[:, c])
+    return sorted(chosen)
+
+
+def render(img_rgb, n, dither_mode, ramp=None):
+    """Return (pen (H,W) 0..n-1, inks (n 6-bit colours), idx (H,W) palette
+    indices, img_lab, plab, prgb)."""
+    plab = g.palette_lab()
+    prgb = g.get_palette().astype(np.uint8)
+    img_lab = c64pal.srgb_to_lab(img_rgb)
+
+    pal_idx = list(ramp) if ramp is not None else choose_inks(img_lab, plab, n)
+    allowed = np.tile(np.array(pal_idx), (*img_lab.shape[:2], 1))
+    idx = dither.quantize(img_lab, allowed, plab, dither_mode).astype(np.int64)
+    lut = {p: k for k, p in enumerate(pal_idx)}
+    pen = np.vectorize(lut.get)(idx).astype(np.uint8)
+    return pen, list(pal_idx), idx.astype(np.uint16), img_lab, plab, prgb
+
+
+def _pack_16(pen):
+    """160x192 pens (0-15) -> 15360 bytes.  2 px/byte, high nibble = left."""
+    scr = bytearray(BYTES_PER_ROW * ROWS)
+    for y in range(ROWS):
+        row = pen[y]
+        base = y * BYTES_PER_ROW
+        for bx in range(BYTES_PER_ROW):
+            scr[base + bx] = (int(row[bx * 2]) << 4) | (int(row[bx * 2 + 1]) & 0x0F)
+    return bytes(scr)
+
+
+def _pack_4(pen):
+    """320x192 pens (0-3) -> 15360 bytes.  4 px/byte, MSB = left."""
+    scr = bytearray(BYTES_PER_ROW * ROWS)
+    for y in range(ROWS):
+        row = pen[y]
+        base = y * BYTES_PER_ROW
+        for bx in range(BYTES_PER_ROW):
+            scr[base + bx] = ((int(row[bx * 4]) << 6) | (int(row[bx * 4 + 1]) << 4) |
+                              (int(row[bx * 4 + 2]) << 2) | int(row[bx * 4 + 3]))
+    return bytes(scr)
+
+
+def _pack_2(pen):
+    """640x192 pens (0-1) -> 15360 bytes.  8 px/byte, MSB = left."""
+    scr = bytearray(BYTES_PER_ROW * ROWS)
+    for y in range(ROWS):
+        row = pen[y]
+        base = y * BYTES_PER_ROW
+        for bx in range(BYTES_PER_ROW):
+            byte = 0
+            for k in range(8):
+                byte |= (int(row[bx * 8 + k]) & 1) << (7 - k)
+            scr[base + bx] = byte
+    return bytes(scr)
+
+
+PACK = {0: _pack_2, 1: _pack_4, 2: _pack_16}    # keyed by CRES