print a PDF on a label (works)

hotprint.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+
+import tempfile
+import subprocess
+from PIL import Image, ImageOps
+
+def convert_pdf(pdfname, args=[]):
+    pbmfile = tempfile.NamedTemporaryFile(suffix='.pbm')
+    subprocess.check_call(["pdftoppm", "-mono", "-singlefile"] + args + [pdfname, pbmfile.name.removesuffix('.pbm')])
+
+    return Image.open(pbmfile)
+
+def convert_pdf_scaled(pdfname, max_width, max_height):
+    im = convert_pdf(pdfname)
+    aspect = im.size[0] / im.size[1]
+    max_aspect = max_width / max_height
+
+    if aspect < max_aspect:
+        max_width = int(max_height * aspect) - 1
+    else:
+        # pdftoppm tends to make it 1px too wide
+        max_width -= 1
+        max_height = int(max_width / aspect)
+
+    args = ['-scale-to-x', str(max_width), '-scale-to-y', str(max_height)]
+    im = convert_pdf(pdfname, args)
+
+    assert im.size[0] <= max_width
+    assert im.size[1] <= max_height
+
+    return im
+
+def label_to_command(image, labelwidth=810, labelheight=1200):
+    "Centre the image on the label and generate a print command"
+    assert im.size[0] <= labelwidth
+    assert im.size[1] <= labelheight
+
+    paste_x = (labelwidth - im.size[0]) // 2
+    paste_y = (labelheight - im.size[1]) // 2
+    row_bytes = (im.size[0] + 7) // 8
+
+    command = b"CLS\r\nBITMAP %d,%d,%d,%d,0," % (paste_x, paste_y, row_bytes, im.size[1])
+    command += image.tobytes()
+    command += b"\r\nPRINT 1,1\r\nSOUND 3,200\r\n"
+    return command
+
+
+im = convert_pdf_scaled("test.pdf", 800, 1200)
+cmd = label_to_command(im)
+with open("/dev/usb/lp0", "r+b") as prn:
+    prn.write(cmd)