First public commit.

lenser/coco/palette.py

@@ -0,0 +1,69 @@
+"""TRS-80 Color Computer MC6847 VDG palette + pixel packing.
+
+PMODE 4 (256x192) is 2-colour: black + the foreground of the selected colour set
+(CSS=0 green, CSS=1 "buff" ~ off-white).  We use CSS=1 (buff on black) for clean
+monochrome, like Apple HGR mono.
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ..palette import srgb_to_lab
+
+# Approximate sRGB for the MC6847 colours.
+BLACK = (0, 0, 0)
+BUFF = (255, 255, 255)
+GREEN = (38, 194, 64)
+YELLOW = (255, 240, 112)
+BLUE = (40, 62, 211)
+RED = (180, 38, 40)
+CYAN = (52, 198, 160)
+MAGENTA = (200, 70, 180)
+ORANGE = (224, 116, 36)
+
+# PMODE 4 monochrome (CSS=1): index 0 = black, 1 = buff.
+MONO = np.array([BLACK, BUFF], dtype=np.float64)
+
+# PMODE 3 (CG6) 4-colour sets, selected by the CSS bit. The 2-bit pixel value
+# 0..3 indexes the set. VDG byte ($FF22) high nibble = E (A/G,GM2,GM1=1, GM0=0).
+PMODE3_SETS = {
+    0xE0: np.array([GREEN, YELLOW, BLUE, RED], dtype=np.float64),       # CSS=0
+    0xE8: np.array([BUFF, CYAN, MAGENTA, ORANGE], dtype=np.float64),    # CSS=1
+}
+
+
+def mono_lab() -> np.ndarray:
+    return srgb_to_lab(MONO)
+
+
+def pack_pmode3(val: np.ndarray) -> bytes:
+    """Pack a (192,128) 0..3 array into 6144 bytes, 4 pixels/byte (2bpp),
+    leftmost pixel in the high bits."""
+    h, w = val.shape
+    out = bytearray(w // 4 * h)
+    k = 0
+    for y in range(h):
+        row = val[y]
+        for x in range(0, w, 4):
+            out[k] = ((row[x] & 3) << 6) | ((row[x + 1] & 3) << 4) | \
+                     ((row[x + 2] & 3) << 2) | (row[x + 3] & 3)
+            k += 1
+    return bytes(out)
+
+
+def pack_pmode4(idx: np.ndarray) -> bytes:
+    """Pack a (192,256) 0/1 array into 6144 bytes, 8 pixels/byte, bit7 leftmost,
+    1 = foreground (the VDG reads this straight from video RAM)."""
+    h, w = idx.shape
+    out = bytearray(w // 8 * h)
+    k = 0
+    for y in range(h):
+        row = idx[y]
+        for x in range(0, w, 8):
+            b = 0
+            for i in range(8):
+                b = (b << 1) | (1 if row[x + i] else 0)
+            out[k] = b
+            k += 1
+    return bytes(out)