Creating High‑Quality Vector PDFs with Cairo’s PDF Surface API

Desired Outcome

Generate a print‑ready PDF that preserves vector graphics, sharp text, and embedded fonts by using Cairo’s cairo_pdf_surface_create API.

Prerequisites

• Cairo 1.16+ compiled with PDF support (check with cairo_info or pkg-config --modversion cairo).
• Write permission to the directory where the PDF will be created.
• Basic knowledge of the C API: cairo_t, cairo_surface_t, and the drawing functions.

Step‑by‑Step Procedure

1. Verify PDF backend availability
   Run cairo_info | grep PDF on the target system. If it reports "PDF: no" you must rebuild Cairo with --enable-pdf or install a package that includes it.
2. Create the PDF surface
   

   cairo_surface_t *pdf = cairo_pdf_surface_create("output.pdf", 595.0, 842.0); // A4 in points
   if (pdf == NULL) {
       fprintf(stderr, "Failed to create PDF surface.\n");
       exit(1);
   }
   

3. Set antialiasing for crisp text
   

   cairo_t *cr = cairo_create(pdf);
    cairo_set_antialias(cr, CAIRO_ANTIALIAS_SUBPIXEL);
   

4. Apply a global transformation (optional)
   Use the matrix to scale or rotate the entire page, e.g., to flip the Y‑axis so that the origin is at the bottom‑left:

   cairo_matrix_t mat;
    cairo_matrix_init_identity(&mat);
    cairo_matrix_translate(&mat, 0, 842.0); // move origin up
    cairo_matrix_scale(&mat, 1, -1);           // flip Y
    cairo_set_matrix(cr, &mat);
   

5. Draw content
   Example: a rectangle and a text string.

   cairo_set_source_rgb(cr, 0, 0, 0); // black
   cairo_rectangle(cr, 50, 50, 200, 100);
   cairo_stroke(cr);
   
   cairo_select_font_face(cr, "Arial", CAIRO_FONT_SLANT_NORMAL, CAIRO_FONT_WEIGHT_BOLD);
   cairo_set_font_size(cr, 24);
   cairo_move_to(cr, 60, 120);
   cairo_show_text(cr, "Hello, Cairo PDF!");
   

6. Finish the surface
   This flushes all pending drawing commands and writes the file atomically.

   cairo_surface_finish(pdf);
    c
   cairo_destroy(cr);
    cairo_surface_destroy(pdf);
   

7. Compile the program
   

   gcc -o cairo_pdf_example cairo_pdf_example.c $(pkg-config --cflags --libs cairo)
   

Expected Checks

• Open output.pdf in a PDF viewer. Text should be sharp, and the rectangle should appear fully vector‑based.
• Run pdfinfo output.pdf to confirm the page size and that fonts are embedded (look for "Embedded") or note the fallback.
• Inspect the file header with head -n 1 output.pdf – it should start with %PDF-1.4.

Recovery Options

• Missing PDF backend
  Recompile Cairo with ./configure --enable-pdf or install libcairo2-dev that includes PDF support.
• Font embedding problems
  Ensure the font file is available on the system or embed it manually using cairo_font_face_create_for_ttf (requires cairo_font_face_t support).
• Corrupted PDF due to abrupt termination
  Always call cairo_surface_finish before exiting. If the program crashes, the PDF may be incomplete; check the file size and try opening it again.

Limitations & Practical Test

While Cairo’s PDF surface preserves vector data, it will fallback to a generic font if the requested font is missing. This can shift text metrics and alter layout. A quick test: remove the Arial font from the system, rebuild, and observe that the PDF still opens but the text may shift or change style.

For high‑density displays, CAIRO_ANTIALIAS_SUBPIXEL gives the best visual quality, but it may increase rendering time. If performance is critical, consider CAIRO_ANTIALIAS_GRAY as a lighter alternative.

To verify that the PDF is truly vector‑based, open the file in a text editor and search for PDF drawing operators such as re (rectangle) or Tj (text). If the file contains these, the content is vector‑encoded.

Conclusion

By following the steps above you can produce a clean, vector PDF from Cairo that retains high‑resolution text, scalable graphics, and embedded fonts. The key points are ensuring PDF support in Cairo, setting sub‑pixel antialiasing, and properly finishing the surface to avoid corruption.