First public commit.

lenser/apple/palette.py

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+"""Apple II colour palettes and the HGR memory-layout helper.
+
+- HGR mono: black/white (the 280x192 1-bit bitmap displayed as monochrome).
+- HGR colour: 6 NTSC "artifact" colours (added later).
+- DHGR: 16 colours (added later).
+"""
+
+from __future__ import annotations
+
+import numpy as np
+
+from ..palette import srgb_to_lab
+
+# Monochrome (white phosphor) pair.
+MONO = np.array([(0, 0, 0), (255, 255, 255)], dtype=np.float64)
+
+# Double-Hi-Res 16-colour palette, indexed by the 4-bit value -- measured from
+# MAME's apple2ee DHGR output so the encoder's nibble values map to exactly what
+# the //e displays.
+DHGR16 = np.array([
+    (0x00, 0x00, 0x00),   # 0  black
+    (0x40, 0x1c, 0xf7),   # 1  blue
+    (0x00, 0x74, 0x40),   # 2  dark green
+    (0x19, 0x90, 0xff),   # 3  medium blue
+    (0x40, 0x63, 0x00),   # 4  olive / dark green
+    (0x80, 0x80, 0x80),   # 5  grey
+    (0x19, 0xd7, 0x00),   # 6  green
+    (0x58, 0xf4, 0xbf),   # 7  aqua
+    (0xa7, 0x0b, 0x40),   # 8  dark red / magenta
+    (0xe6, 0x28, 0xff),   # 9  magenta / violet
+    (0x80, 0x80, 0x80),   # 10 grey
+    (0xbf, 0x9c, 0xff),   # 11 lavender
+    (0xe6, 0x6f, 0x00),   # 12 orange
+    (0xff, 0x8b, 0xbf),   # 13 pink
+    (0xbf, 0xe3, 0x08),   # 14 yellow-green
+    (0xff, 0xff, 0xff),   # 15 white
+], dtype=np.float64)
+
+
+# HGR NTSC "artifact" colours.  Per 7-pixel byte a palette bit selects one of two
+# colour pairs; the displayed colour of an "on" pixel also depends on its column
+# parity (and two adjacent on-pixels read as white).
+#   palette 0: even column -> violet, odd column -> green
+#   palette 1: even column -> blue,   odd column -> orange
+HGR_BLACK, HGR_VIOLET, HGR_GREEN, HGR_WHITE, HGR_BLUE, HGR_ORANGE = 0, 1, 2, 3, 4, 5
+HGR6 = np.array([
+    (0x00, 0x00, 0x00),   # black
+    (0xd0, 0x3a, 0xff),   # violet
+    (0x20, 0xc8, 0x00),   # green
+    (0xff, 0xff, 0xff),   # white
+    (0x20, 0x9a, 0xff),   # blue
+    (0xff, 0x6a, 0x20),   # orange
+], dtype=np.float64)
+
+
+def mono_lab() -> np.ndarray:
+    return srgb_to_lab(MONO)
+
+
+def hgr6_lab() -> np.ndarray:
+    return srgb_to_lab(HGR6)
+
+
+def pack_hgr_color(bits280: np.ndarray, pal_byte: np.ndarray) -> bytes:
+    """280x192 mono bits + (192x40) per-byte palette bit -> 8192 HGR buffer."""
+    buf = bytearray(0x2000)
+    H = bits280.shape[0]
+    for y in range(H):
+        base = hgr_row_addr(y)
+        row = bits280[y]
+        for bx in range(40):
+            b = 0
+            for i in range(7):
+                if row[bx * 7 + i]:
+                    b |= (1 << i)
+            if pal_byte[y, bx]:
+                b |= 0x80
+            buf[base + bx] = b
+    return bytes(buf)
+
+
+def dhgr_lab() -> np.ndarray:
+    return srgb_to_lab(DHGR16)
+
+
+def hgr_row_addr(y: int) -> int:
+    """Offset (from $2000) of HGR row ``y`` (0..191) in the interleaved layout."""
+    return (y & 7) * 0x400 + ((y >> 3) & 7) * 0x80 + (y >> 6) * 0x28
+
+
+def pack_hgr_mono(val_image: np.ndarray) -> bytes:
+    """280x192 1-bit image -> 8192-byte HGR page 1 buffer.
+
+    7 pixels per byte, bit 0 = leftmost, bit 7 (palette bit) = 0 for mono.
+    """
+    buf = bytearray(0x2000)
+    H, W = val_image.shape
+    for y in range(H):
+        base = hgr_row_addr(y)
+        row = val_image[y]
+        for bx in range(40):
+            b = 0
+            for i in range(7):
+                if row[bx * 7 + i]:
+                    b |= (1 << i)
+            buf[base + bx] = b
+    return bytes(buf)