add REAL_VIEWFINDER setting to size and center the live preview

Sizes the curses viewfinder box to match the print output's character
grid (A4/roll-paper target dims) instead of always filling the
terminal, and always centers the box. Defaults to true.

ascii.conf

@@ -18,6 +18,14 @@ NEGATIVE=false
 FLIP_X=false
 FLIP_Y=false
 
+# Size the live-preview viewfinder box to the same character grid as the
+# final print output (see PRINTER_A4/PRINTER_MAX_LINES/PRINTER_MAX_COLS in
+# printer.conf) instead of just filling the terminal. The preview frame is
+# still cropped/converted on its own, upright, before any print-time
+# rotation - only the box's cols/rows match the output. The viewfinder is
+# always centered in the terminal either way. (true/false)
+REAL_VIEWFINDER=true
+
 # Color and braille output are intentionally not exposed here: both rely on
 # ANSI/multi-byte Unicode that a parallel-port needle printer can't render.
 # Only add --color/--braille yourself if you don't plan to print via

photobooth.py

@@ -79,6 +79,7 @@ class Config:
         self.negative = as_bool(ascii_.get("NEGATIVE"))
         self.flip_x = as_bool(ascii_.get("FLIP_X"))
         self.flip_y = as_bool(ascii_.get("FLIP_Y"))
+        self.real_viewfinder = as_bool(ascii_.get("REAL_VIEWFINDER"))
 
         self.printer_a4 = as_bool(printer.get("PRINTER_A4"))
         self.printer_max_lines = int(printer.get("PRINTER_MAX_LINES", "64") or 64)
@@ -177,8 +178,28 @@ def capture_label(cfg):
     return "space" if cfg.key_capture == " " else cfg.key_capture
 
 
-def box_dims_for(term_rows, term_cols):
-    return max(term_rows - 2, 3), max(term_cols, 10)
+def output_target_dims(cfg, inner_cols, inner_rows):
+    """cols/rows the print/output pipeline sizes a capture to (see prepare_print_frame)."""
+    if cfg.printer_max_lines == 0:
+        return cfg.printer_max_cols, None
+    if cfg.printer_a4:
+        return cfg.printer_max_cols, cfg.printer_max_lines
+    return inner_cols, inner_rows
+
+
+def box_dims_for(term_rows, term_cols, cfg=None):
+    max_rows, max_cols = max(term_rows - 2, 3), max(term_cols, 10)
+    if cfg is None or not cfg.real_viewfinder:
+        return max_rows, max_cols
+    target_cols, target_rows = output_target_dims(cfg, max_cols - 2, max_rows - 2)
+    rows = max_rows if target_rows is None else max(min(target_rows + 2, max_rows), 3)
+    cols = max(min(target_cols + 2, max_cols), 10)
+    return rows, cols
+
+
+def box_origin(term_rows, term_cols, box_rows, box_cols):
+    """Top-left corner that centers a box_rows x box_cols window in the terminal."""
+    return max((term_rows - box_rows) // 2, 0), max((term_cols - box_cols) // 2, 0)
 
 
 _CHAR_ASPECT = 0.5  # width:height ratio of a typical monospace glyph cell
@@ -210,23 +231,21 @@ def prepare_print_frame(frame, cfg, inner_cols, inner_rows):
     first and mangling already-rendered ascii text, which doesn't account
     for non-square character cells and reads as visibly distorted.
     """
-    if cfg.printer_max_lines == 0:
+    cols, rows = output_target_dims(cfg, inner_cols, inner_rows)
+    if rows is None:
         # Roll printer: paper feeds continuously, so there's no page height
         # to crop to - only the carriage width (PRINTER_MAX_COLS) limits the
         # print. Leave the frame uncropped and pass rows=None downstream so
         # ascii-image-converter derives height from the image's own aspect
         # ratio instead of forcing a row count.
-        cols, rows = cfg.printer_max_cols, None
         if cfg.printer_a4:
             frame = cv2.rotate(frame, cv2.ROTATE_90_CLOCKWISE)
     elif cfg.printer_a4:
-        cols, rows = cfg.printer_max_cols, cfg.printer_max_lines
         # Cropping happens before the 90-degree rotation below, which swaps
         # width and height, so crop to the inverse of the final aspect ratio.
         frame = crop_to_aspect(frame, 1 / visual_aspect(cols, rows))
         frame = cv2.rotate(frame, cv2.ROTATE_90_CLOCKWISE)
     else:
-        cols, rows = inner_cols, inner_rows
         frame = crop_to_aspect(frame, visual_aspect(cols, rows))
     return frame, cols, rows
 
@@ -253,8 +272,9 @@ def main(stdscr):
     frame_times = []
     message, message_until = "", 0.0
     rows, cols = stdscr.getmaxyx()
-    box_dims = box_dims_for(rows, cols)
-    box_win = curses.newwin(box_dims[0], box_dims[1], 0, 0)
+    box_dims = box_dims_for(rows, cols, cfg)
+    box_pos = box_origin(rows, cols, *box_dims)
+    box_win = curses.newwin(*box_dims, *box_pos)
 
     try:
         while True:
@@ -268,12 +288,14 @@ def main(stdscr):
             fps = len(frame_times)
 
             rows, cols = stdscr.getmaxyx()
-            box_rows, box_cols = box_dims_for(rows, cols)
+            box_rows, box_cols = box_dims_for(rows, cols, cfg)
             inner_rows, inner_cols = max(box_rows - 2, 1), max(box_cols - 2, 1)
+            box_pos_now = box_origin(rows, cols, box_rows, box_cols)
 
-            if (box_rows, box_cols) != box_dims:
-                box_win = curses.newwin(box_rows, box_cols, 0, 0)
+            if (box_rows, box_cols) != box_dims or box_pos_now != box_pos:
+                box_win = curses.newwin(box_rows, box_cols, *box_pos_now)
                 box_dims = (box_rows, box_cols)
+                box_pos = box_pos_now
                 stdscr.erase()
 
             # Live preview: always upright, cropped to roughly the box's own
@@ -306,9 +328,10 @@ def main(stdscr):
                 f"[{cfg.key_reset}] reset  [{capture_label(cfg)}] capture  "
                 f"[{cfg.key_quit}] quit "
             )
+            status_y = box_pos[0] + box_rows
             try:
-                stdscr.addstr(box_rows, 0, status[:cols].ljust(cols))
-                stdscr.addstr(box_rows + 1, 0, help_line[:cols].ljust(cols - 1))
+                stdscr.addstr(status_y, 0, status[:cols].ljust(cols))
+                stdscr.addstr(status_y + 1, 0, help_line[:cols].ljust(cols - 1))
             except curses.error:
                 pass
             stdscr.refresh()