generate-alt-random: emit multiple sixel bands

This ensures we’re getting the ‘$’ command PGO:d

scripts/generate-alt-random-writes.py

@@ -165,7 +165,7 @@ def main():
         # The sixel 'alphabet'
         sixels = '?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~'
 
-        for _ in range(200):
+        for _ in range(100):
             # Offset image
             out.write(' ' * (random.randrange(cols // 2)))
 
@@ -188,6 +188,8 @@ def main():
             out.write(f'"1;1;{six_width};{six_height}')
 
             for row in range(six_height // 6):  # Each sixel is 6 pixels
+                band_count = random.randrange(32)
+                for band in range(band_count):
                     # Choose a random color
                     out.write(f'#{random.randrange(256)}')
 
@@ -198,6 +200,11 @@ def main():
                         out.write(f'!{six_width}{random.choice(sixels)}')
 
                     # Next line
+                    if band + 1 < band_count:
+                        # Move cursor to beginning of current row
+                        out.write('$')
+                    elif row + 1 < six_height // 6:
+                        # Newline
                         out.write('-')
 
             # End sixel