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comic/imaging.py

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+"""Assemble a FLUX image prompt for one panel, and a deterministic seed.
+
+Character consistency is the hard part of a multi-panel comic: FLUX renders every
+panel independently, so the only lever we have to keep a character looking the same
+across 20 images is to feed its FIXED visual description (from the bible) verbatim
+into every panel it appears in. So a panel prompt is, in order:
+
+    <art style>, comic book panel, <scene>, <appearance of each character present>,
+    <palette>, <text-free contract>
+
+The art style + palette are constant across the whole comic (style consistency);
+the per-character appearance is constant per character (character consistency);
+only the scene varies panel to panel (story variety).
+"""
+
+from __future__ import annotations
+
+import hashlib
+
+from .schema import Panel, ComicBible
+
+# FLUX bakes garbled letters if asked for signage; the distilled model ignores
+# negative prompts, so the "no text" contract lives in the positive prompt. The UI
+# renders captions separately, so we never want text inside the image.
+TEXT_FREE = (
+    "no text, no speech bubbles, no captions, no lettering or words anywhere in the image"
+)
+
+# A sane default if the writer omitted a style/palette.
+DEFAULT_STYLE = (
+    "modern western comic book art, bold confident black ink linework, dynamic "
+    "cel shading, clean dramatic composition"
+)
+DEFAULT_PALETTE = "rich saturated comic-book color palette"
+
+
+def _appearance_clause(panel: Panel, bible: ComicBible) -> str:
+    """The verbatim fixed appearance text for each named character in this panel.
+
+    This is the consistency anchor — same words every time a character appears.
+    """
+    clauses = []
+    for name in panel.characters:
+        ch = bible.character(name)
+        if ch is not None and ch.appearance:
+            clauses.append(f"{ch.name}: {ch.appearance}")
+    return "; ".join(clauses)
+
+
+def build_image_prompt(panel: Panel, bible: ComicBible) -> str:
+    """Full FLUX prompt for one panel (idempotent; also stored on panel.image_prompt)."""
+    style = bible.art_style or DEFAULT_STYLE
+    palette = bible.palette or DEFAULT_PALETTE
+    scene = (panel.scene or "").strip().rstrip(".")
+    chars = _appearance_clause(panel, bible)
+
+    parts = [style, "comic book panel", scene]
+    if chars:
+        parts.append(chars)
+    parts += [palette, TEXT_FREE]
+    return ", ".join(p for p in parts if p and p.strip())
+
+
+def panel_seed(bible: ComicBible, panel: Panel) -> int:
+    """Deterministic per-panel seed (stable across reruns, distinct per panel).
+
+    Keyed on the title + panel index so the same comic re-renders identically and
+    no two panels collide on a seed.
+    """
+    key = f"{bible.title}|{panel.index}".encode("utf-8")
+    digest = hashlib.sha256(key).digest()
+    return int.from_bytes(digest[:4], "big") & 0x7FFFFFFF