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Introduction

PDFio is a simple C library for reading and writing PDF files. The primary goals of pdfio are:

  • Read and write any version of PDF file
  • Provide access to pages, objects, and streams within a PDF file
  • Support reading and writing of encrypted PDF files
  • Extract or embed useful metadata (author, creator, page information, etc.)
  • "Filter" PDF files, for example to extract a range of pages or to embed fonts that are missing from a PDF
  • Provide access to objects used for each page

PDFio is not concerned with rendering or viewing a PDF file, although a PDF RIP or viewer could be written using it.

PDFio is Copyright © 2021-2024 by Michael R Sweet and is licensed under the Apache License Version 2.0 with an (optional) exception to allow linking against GPL2/LGPL2 software. See the files "LICENSE" and "NOTICE" for more information.

Requirements

PDFio requires the following to build the software:

  • A C99 compiler such as Clang, GCC, or MS Visual C
  • A POSIX-compliant make program
  • A POSIX-compliant sh program
  • ZLIB (https://www.zlib.net) 1.0 or higher

IDE files for Xcode (macOS/iOS) and Visual Studio (Windows) are also provided.

Installing PDFio

PDFio comes with a configure script that creates a portable makefile that will work on any POSIX-compliant system with ZLIB installed. To make it, run:

./configure
make

To test it, run:

make test

To install it, run:

sudo make install

If you want a shared library, run:

./configure --enable-shared
make
sudo make install

The default installation location is "/usr/local". Pass the --prefix option to make to install it to another location:

./configure --prefix=/some/other/directory

Other configure options can be found using the --help option:

./configure --help

Visual Studio Project

The Visual Studio solution ("pdfio.sln") is provided for Windows developers and generates both a static library and DLL.

Xcode Project

There is also an Xcode project ("pdfio.xcodeproj") you can use on macOS which generates a static library that will be installed under "/usr/local" with:

sudo xcodebuild install

Detecting PDFio

PDFio can be detected using the pkg-config command, for example:

if pkg-config --exists pdfio; then
    ...
fi

In a makefile you can add the necessary compiler and linker options with:

CFLAGS  +=      `pkg-config --cflags pdfio`
LIBS    +=      `pkg-config --libs pdfio`

On Windows, you need to link to the PDFIO1.LIB (DLL) library and include the zlib_native NuGet package dependency. You can also use the published pdfio_native NuGet package.

Header Files

PDFio provides a primary header file that is always used:

#include <pdfio.h>

PDFio also provides PDF content helper functions for producing PDF content that are defined in a separate header file:

#include <pdfio-content.h>

Understanding PDF Files

A PDF file provides data and commands for displaying pages of graphics and text, and is structured in a way that allows it to be displayed in the same way across multiple devices and platforms. The following is a PDF which shows "Hello, World!" on one page:

%PDF-1.0                        % Header starts here
%âãÏÓ
1 0 obj                         % Body starts here
<<
/Kids [2 0 R]
/Count 1
/Type /Pages
>>
endobj
2 0 obj
<<
/Rotate 0
/Parent 1 0 R
/Resources 3 0 R
/MediaBox [0 0 612 792]
/Contents [4 0 R]/Type /Page
>>
endobj
3 0 obj
<<
/Font
<<
/F0
<<
/BaseFont /Times-Italic
/Subtype /Type1
/Type /Font
>>
>>
>>
endobj
4 0 obj
<<
/Length 65
>>
stream
1. 0. 0. 1. 50. 700. cm
BT
  /F0 36. Tf
  (Hello, World!) Tj
ET
endstream
endobj
5 0 obj
<<
/Pages 1 0 R
/Type /Catalog
>>
endobj
xref                            % Cross-reference table starts here
0 6
0000000000 65535 f
0000000015 00000 n
0000000074 00000 n
0000000192 00000 n
0000000291 00000 n
0000000409 00000 n
trailer                         % Trailer starts here
<<
/Root 5 0 R
/Size 6
>>
startxref
459
%%EOF

Header

The header is the first line of a PDF file that specifies the version of the PDF format that has been used, for example %PDF-1.0.

Since PDF files almost always contain binary data, they can become corrupted if line endings are changed. For example, if the file is transferred using FTP in text mode or is edited in Notepad on Windows. To allow legacy file transfer programs to determine that the file is binary, the PDF standard recommends including some bytes with character codes higher than 127 in the header, for example:

%âãÏÓ

The percent sign indicates a comment line while the other few bytes are arbitrary character codes in excess of 127. So, the whole header in our example is:

%PDF-1.0
%âãÏÓ

Body

The file body consists of a sequence of objects, each preceded by an object number, generation number, and the obj keyword on one line, and followed by the endobj keyword on another. For example:

1 0 obj
<<
/Kids [2 0 R]
/Count 1
/Type /Pages
>>
endobj

In this example, the object number is 1 and the generation number is 0, meaning it is the first version of the object. The content for object 1 is between the initial 1 0 obj and trailing endobj lines. In this case, the content is the dictionary <</Kids [2 0 R] /Count 1 /Type /Pages>>.

Cross-Reference Table

The cross-reference table lists the byte offset of each object in the file body. This allows random access to objects, meaning they don't have to be read in order. Objects that are not used are never read, making the process efficient. Operations like counting the number of pages in a PDF document are fast, even in large files.

Each object has an object number and a generation number. Generation numbers are used when a cross-reference table entry is reused. For simplicity, we will assume generation numbers to be always zero and ignore them. The cross-reference table consists of a header line that indicates the number of entries, a free entry line for object 0, and a line for each of the objects in the file body. For example:

0 6                             % Six entries in table, starting at 0
0000000000 65535 f              % Free entry for object 0
0000000015 00000 n              % Object 1 is at byte offset 15
0000000074 00000 n              % Object 2 is at byte offset 74
0000000192 00000 n              % etc...
0000000291 00000 n
0000000409 00000 n              % Object 5 is at byte offset 409

Trailer

The first line of the trailer is just the trailer keyword. This is followed by the trailer dictionary which contains at least the /Size entry specifying the number of entries in the cross-reference table and the /Root entry which references the object for the document catalog which is the root element of the graph of objects in the body.

There follows a line with just the startxref keyword, a line with a single number specifying the byte offset of the start of the cross-reference table within the file, and then the line %%EOF which signals the end of the PDF file.

trailer                         % Trailer keyword
<<                              % The trailer dictinonary
/Root 5 0 R
/Size 6
>>
startxref                       % startxref keyword
459                             % Byte offset of cross-reference table
%%EOF                           % End-of-file marker

API Overview

PDFio exposes several types:

  • pdfio_file_t: A PDF file (for reading or writing)
  • pdfio_array_t: An array of values
  • pdfio_dict_t: A dictionary of key/value pairs in a PDF file, object, etc.
  • pdfio_obj_t: An object in a PDF file
  • pdfio_stream_t: An object stream

Reading PDF Files

You open an existing PDF file using the pdfioFileOpen function:

pdfio_file_t *pdf =
    pdfioFileOpen("myinputfile.pdf", password_cb, password_data,
                  error_cb, error_data);

where the five arguments to the function are the filename ("myinputfile.pdf"), an optional password callback function (password_cb) and data pointer value (password_data), and an optional error callback function (error_cb) and data pointer value (error_data). The password callback is called for encrypted PDF files that are not using the default password, for example:

const char *
password_cb(void *data, const char *filename)
{
  (void)data;     // This callback doesn't use the data pointer
  (void)filename; // This callback doesn't use the filename

  // Return a password string for the file...
  return ("Password42");
}

The error callback is called for both errors and warnings and accepts the pdfio_file_t pointer, a message string, and the callback pointer value, for example:

bool
error_cb(pdfio_file_t *pdf, const char *message, void *data)
{
  (void)data; // This callback does not use the data pointer

  fprintf(stderr, "%s: %s\n", pdfioFileGetName(pdf), message);

  // Return false to treat warnings as errors
  return (false);
}

The default error callback (NULL) does the equivalent of the above.

Each PDF file contains one or more pages. The pdfioFileGetNumPages function returns the number of pages in the file while the pdfioFileGetPage function gets the specified page in the PDF file:

pdfio_file_t *pdf;   // PDF file
size_t       i;      // Looping var
size_t       count;  // Number of pages
pdfio_obj_t  *page;  // Current page

// Iterate the pages in the PDF file
for (i = 0, count = pdfioFileGetNumPages(pdf); i < count; i ++)
{
  page = pdfioFileGetPage(pdf, i);
  // do something with page
}

Each page is represented by a "page tree" object (what pdfioFileGetPage returns) that specifies information about the page and one or more "content" objects that contain the images, fonts, text, and graphics that appear on the page. Use the pdfioPageGetNumStreams and pdfioPageOpenStream functions to access the content streams for each page, and pdfioObjGetDict to get the associated page object dictionary. For example, if you want to display the media and crop boxes for a given page:

pdfio_file_t  *pdf;             // PDF file
size_t        i;                // Looping var
size_t        count;            // Number of pages
pdfio_obj_t   *page;            // Current page
pdfio_dict_t  *dict;            // Current page dictionary
pdfio_array_t *media_box;       // MediaBox array
double        media_values[4];  // MediaBox values
pdfio_array_t *crop_box;        // CropBox array
double        crop_values[4];   // CropBox values

// Iterate the pages in the PDF file
for (i = 0, count = pdfioFileGetNumPages(pdf); i < count; i ++)
{
  page = pdfioFileGetPage(pdf, i);
  dict = pdfioObjGetDict(page);

  media_box       = pdfioDictGetArray(dict, "MediaBox");
  media_values[0] = pdfioArrayGetNumber(media_box, 0);
  media_values[1] = pdfioArrayGetNumber(media_box, 1);
  media_values[2] = pdfioArrayGetNumber(media_box, 2);
  media_values[3] = pdfioArrayGetNumber(media_box, 3);

  crop_box       = pdfioDictGetArray(dict, "CropBox");
  crop_values[0] = pdfioArrayGetNumber(crop_box, 0);
  crop_values[1] = pdfioArrayGetNumber(crop_box, 1);
  crop_values[2] = pdfioArrayGetNumber(crop_box, 2);
  crop_values[3] = pdfioArrayGetNumber(crop_box, 3);

  printf("Page %u: MediaBox=[%g %g %g %g], CropBox=[%g %g %g %g]\n",
         (unsigned)(i + 1),
         media_values[0], media_values[1], media_values[2], media_values[3],
         crop_values[0], crop_values[1], crop_values[2], crop_values[3]);
}

Page object dictionaries have several (mostly optional) key/value pairs, including:

  • "Annots": An array of annotation dictionaries for the page; use pdfioDictGetArray to get the array
  • "CropBox": The crop box as an array of four numbers for the left, bottom, right, and top coordinates of the target media; use pdfioDictGetArray to get a pointer to the array of numbers
  • "Dur": The number of seconds the page should be displayed; use pdfioDictGetNumber to get the page duration value
  • "Group": The dictionary of transparency group values for the page; use pdfioDictGetDict to get a pointer to the resources dictionary
  • "LastModified": The date and time when this page was last modified; use pdfioDictGetDate to get the Unix time_t value
  • "Parent": The parent page tree node object for this page; use pdfioDictGetObj to get a pointer to the object
  • "MediaBox": The media box as an array of four numbers for the left, bottom, right, and top coordinates of the target media; use pdfioDictGetArray to get a pointer to the array of numbers
  • "Resources": The dictionary of resources for the page; use pdfioDictGetDict to get a pointer to the resources dictionary
  • "Rotate": A number indicating the number of degrees of counter-clockwise rotation to apply to the page when viewing; use pdfioDictGetNumber to get the rotation angle
  • "Thumb": A thumbnail image object for the page; use pdfioDictGetObj to get a pointer to the thumbnail image object
  • "Trans": The page transition dictionary; use pdfioDictGetDict to get a pointer to the dictionary

The pdfioFileClose function closes a PDF file and frees all memory that was used for it:

pdfioFileClose(pdf);

Writing PDF Files

You create a new PDF file using the pdfioFileCreate function:

pdfio_rect_t media_box = { 0.0, 0.0, 612.0, 792.0 };  // US Letter
pdfio_rect_t crop_box = { 36.0, 36.0, 576.0, 756.0 }; // w/0.5" margins

pdfio_file_t *pdf = pdfioFileCreate("myoutputfile.pdf", "2.0",
                                    &media_box, &crop_box,
                                    error_cb, error_data);

where the six arguments to the function are the filename ("myoutputfile.pdf"), PDF version ("2.0"), media box (media_box), crop box (crop_box), an optional error callback function (error_cb), and an optional pointer value for the error callback function (error_data). The units for the media and crop boxes are points (1/72nd of an inch).

Alternately you can stream a PDF file using the pdfioFileCreateOutput function:

pdfio_rect_t media_box = { 0.0, 0.0, 612.0, 792.0 };  // US Letter
pdfio_rect_t crop_box = { 36.0, 36.0, 576.0, 756.0 }; // w/0.5" margins

pdfio_file_t *pdf = pdfioFileCreateOutput(output_cb, output_ctx, "2.0",
                                          &media_box, &crop_box,
                                          error_cb, error_data);

Once the file is created, use the pdfioFileCreateObj, pdfioFileCreatePage, and pdfioPageCopy functions to create objects and pages in the file.

Finally, the pdfioFileClose function writes the PDF cross-reference and "trailer" information, closes the file, and frees all memory that was used for it.

PDF Objects

PDF objects are identified using two numbers - the object number (1 to N) and the object generation (0 to 65535) that specifies a particular version of an object. An object's numbers are returned by the pdfioObjGetNumber and pdfioObjGetGeneration functions. You can find a numbered object using the pdfioFileFindObj function.

Objects contain values (typically dictionaries) and usually an associated data stream containing images, fonts, ICC profiles, and page content. PDFio provides several accessor functions to get the value(s) associated with an object:

PDF Streams

Some PDF objects have an associated data stream, such as for pages, images, ICC color profiles, and fonts. You access the stream for an existing object using the pdfioObjOpenStream function:

pdfio_file_t *pdf = pdfioFileOpen(...);
pdfio_obj_t *obj = pdfioFileFindObj(pdf, number);
pdfio_stream_t *st = pdfioObjOpenStream(obj, true);

The first argument is the object pointer. The second argument is a boolean value that specifies whether you want to decode (typically decompress) the stream data or return it as-is.

When reading a page stream you'll use the pdfioPageOpenStream function instead:

pdfio_file_t *pdf = pdfioFileOpen(...);
pdfio_obj_t *obj = pdfioFileGetPage(pdf, number);
pdfio_stream_t *st = pdfioPageOpenStream(obj, 0, true);

Once you have the stream open, you can use one of several functions to read from it:

When you are done reading from the stream, call the pdfioStreamClose function:

pdfioStreamClose(st);

To create a stream for a new object, call the pdfioObjCreateStream function:

pdfio_file_t *pdf = pdfioFileCreate(...);
pdfio_obj_t *obj = pdfioFileCreateObj(pdf, ...);
pdfio_stream_t *st = pdfioObjCreateStream(obj, PDFIO_FILTER_FLATE);

The first argument is the newly created object. The second argument is either PDFIO_FILTER_NONE to specify that any encoding is done by your program or PDFIO_FILTER_FLATE to specify that PDFio should Flate compress the stream.

To create a page content stream call the pdfioFileCreatePage function:

pdfio_file_t *pdf = pdfioFileCreate(...);
pdfio_dict_t *dict = pdfioDictCreate(pdf);
... set page dictionary keys and values ...
pdfio_stream_t *st = pdfioFileCreatePage(pdf, dict);

Once you have created the stream, use any of the following functions to write to the stream:

The PDF content helper functions provide additional functions for writing specific PDF page stream commands.

When you are done writing the stream, call pdfioStreamClose to close both the stream and the object.

PDF Content Helper Functions

PDFio includes many helper functions for embedding or writing specific kinds of content to a PDF file. These functions can be roughly grouped into five categories:

Color Space Functions

PDF color spaces are specified using well-known names like "DeviceCMYK", "DeviceGray", and "DeviceRGB" or using arrays that define so-called calibrated color spaces. PDFio provides several functions for embedding ICC profiles and creating color space arrays:

You can embed an ICC color profile using the pdfioFileCreateICCObjFromFile function:

pdfio_file_t *pdf = pdfioFileCreate(...);
pdfio_obj_t *icc = pdfioFileCreateICCObjFromFile(pdf, "filename.icc");

where the first argument is the PDF file and the second argument is the filename of the ICC color profile.

PDFio also includes predefined constants for creating a few standard color spaces:

pdfio_file_t *pdf = pdfioFileCreate(...);

// Create an AdobeRGB color array
pdfio_array_t *adobe_rgb =
    pdfioArrayCreateColorFromStandard(pdf, 3, PDFIO_CS_ADOBE);

// Create an Display P3 color array
pdfio_array_t *display_p3 =
    pdfioArrayCreateColorFromStandard(pdf, 3, PDFIO_CS_P3_D65);

// Create an sRGB color array
pdfio_array_t *srgb =
    pdfioArrayCreateColorFromStandard(pdf, 3, PDFIO_CS_SRGB);

Font Object Functions

PDF supports many kinds of fonts, including PostScript Type1, PDF Type3, TrueType/OpenType, and CID. PDFio provides two functions for creating font objects. The first is pdfioFileCreateFontObjFromBase which creates a font object for one of the base PDF fonts:

  • "Courier"
  • "Courier-Bold"
  • "Courier-BoldItalic"
  • "Courier-Italic"
  • "Helvetica"
  • "Helvetica-Bold"
  • "Helvetica-BoldOblique"
  • "Helvetica-Oblique"
  • "Symbol"
  • "Times-Bold"
  • "Times-BoldItalic"
  • "Times-Italic"
  • "Times-Roman"
  • "ZapfDingbats"

Except for Symbol and ZapfDingbats (which use a custom 8-bit character set), PDFio always uses the Windows CP1252 subset of Unicode for these fonts.

The second function is pdfioFileCreateFontObjFromFile which creates a font object from a TrueType/OpenType font file, for example:

pdfio_file_t *pdf = pdfioFileCreate(...);
pdfio_obj_t *arial =
    pdfioFileCreateFontObjFromFile(pdf, "OpenSans-Regular.ttf", false);

will embed an OpenSans Regular TrueType font using the Windows CP1252 subset of Unicode. Pass true for the third argument to embed it as a Unicode CID font instead, for example:

pdfio_file_t *pdf = pdfioFileCreate(...);
pdfio_obj_t *arial =
    pdfioFileCreateFontObjFromFile(pdf, "NotoSansJP-Regular.otf", true);

will embed the NotoSansJP Regular OpenType font with full support for Unicode.

Note: Not all fonts support Unicode, and most do not contain a full complement of Unicode characters. pdfioFileCreateFontObjFromFile does not perform any character subsetting, so the entire font file is embedded in the PDF file.

Image Object Functions

PDF supports images with many different color spaces and bit depths with optional transparency. PDFio provides two helper functions for creating image objects that can be referenced in page streams. The first function is pdfioFileCreateImageObjFromData which creates an image object from data in memory, for example:

pdfio_file_t *pdf = pdfioFileCreate(...);
unsigned char data[1024 * 1024 * 4]; // 1024x1024 RGBA image data
pdfio_obj_t *img =
    pdfioFileCreateImageObjFromData(pdf, data, /*width*/1024,
                                    /*height*/1024, /*num_colors*/3,
                                    /*color_data*/NULL, /*alpha*/true,
                                    /*interpolate*/false);

will create an object for a 1024x1024 RGBA image in memory, using the default color space for 3 colors ("DeviceRGB"). We can use one of the color space functions to use a specific color space for this image, for example:

pdfio_file_t *pdf = pdfioFileCreate(...);

// Create an AdobeRGB color array
pdfio_array_t *adobe_rgb =
    pdfioArrayCreateColorFromMatrix(pdf, 3, pdfioAdobeRGBGamma,
                                    pdfioAdobeRGBMatrix,
                                    pdfioAdobeRGBWhitePoint);

// Create a 1024x1024 RGBA image using AdobeRGB
unsigned char data[1024 * 1024 * 4]; // 1024x1024 RGBA image data
pdfio_obj_t *img =
    pdfioFileCreateImageObjFromData(pdf, data, /*width*/1024,
                                    /*height*/1024, /*num_colors*/3,
                                    /*color_data*/adobe_rgb,
                                    /*alpha*/true,
                                    /*interpolate*/false);

The "interpolate" argument specifies whether the colors in the image should be smoothed/interpolated when scaling. This is most useful for photographs but should be false for screenshot and barcode images.

If you have a JPEG or PNG file, use the pdfioFileCreateImageObjFromFile function to copy the image into a PDF image object, for example:

pdfio_file_t *pdf = pdfioFileCreate(...);
pdfio_obj_t *img =
    pdfioFileCreateImageObjFromFile(pdf, "myphoto.jpg",
                                    /*interpolate*/true);

Note: Currently pdfioFileCreateImageObjFromFile does not support 12 bit JPEG files or PNG files with an alpha channel.

Page Dictionary Functions

PDF pages each have an associated dictionary to specify the images, fonts, and color spaces used by the page. PDFio provides functions to add these resources to the dictionary:

Page Stream Functions

PDF page streams contain textual commands for drawing on the page. PDFio provides many functions for writing these commands with the correct format and escaping, as needed:

Examples

Read PDF Metadata

The pdfioinfo.c example program opens a PDF file and prints the title, author, creation date, and number of pages:

#include <pdfio.h>
#include <time.h>


int                                     // O - Exit status
main(int  argc,                         // I - Number of command-line arguments
     char *argv[])                      // Command-line arguments
{
  const char    *filename;              // PDF filename
  pdfio_file_t  *pdf;                   // PDF file
  time_t        creation_date;          // Creation date
  struct tm     *creation_tm;           // Creation date/time information
  char          creation_text[256];     // Creation date/time as a string


  // Get the filename from the command-line...
  if (argc != 2)
  {
    fputs("Usage: ./pdfioinfo FILENAME.pdf\n", stderr);
    return (1);
  }

  filename = argv[1];

  // Open the PDF file with the default callbacks...
  pdf = pdfioFileOpen(filename, /*password_cb*/NULL,
                      /*password_cbdata*/NULL, /*error_cb*/NULL,
                      /*error_cbdata*/NULL);
  if (pdf == NULL)
    return (1);

  // Get the creation date and convert to a string...
  creation_date = pdfioFileGetCreationDate(pdf);
  creation_tm   = localtime(&creation_date);
  strftime(creation_text, sizeof(creation_text), "%c", creation_tm);

  // Print file information to stdout...
  printf("%s:\n", filename);
  printf("         Title: %s\n", pdfioFileGetTitle(pdf));
  printf("        Author: %s\n", pdfioFileGetAuthor(pdf));
  printf("    Created On: %s\n", creation_text);
  printf("  Number Pages: %u\n", (unsigned)pdfioFileGetNumPages(pdf));

  // Close the PDF file...
  pdfioFileClose(pdf);

  return (0);
}

Create PDF File With Text and Image

The image2pdf.c example code creates a PDF file containing a JPEG or PNG image file and optional caption on a single page. The create_pdf_image_file function creates the PDF file, embeds a base font and the named JPEG or PNG image file, and then creates a page with the image centered on the page with any text centered below:

#include <pdfio.h>
#include <pdfio-content.h>
#include <string.h>


bool                                    // O - True on success, false on failure
create_pdf_image_file(
    const char *pdfname,                // I - PDF filename
    const char *imagename,              // I - Image filename
    const char *caption)                // I - Caption filename
{
  pdfio_file_t   *pdf;                  // PDF file
  pdfio_obj_t    *font;                 // Caption font
  pdfio_obj_t    *image;                // Image
  pdfio_dict_t   *dict;                 // Page dictionary
  pdfio_stream_t *page;                 // Page stream
  double         width, height;         // Width and height of image
  double         swidth, sheight;       // Scaled width and height on page
  double         tx, ty;                // Position on page


  // Create the PDF file...
  pdf = pdfioFileCreate(pdfname, /*version*/NULL, /*media_box*/NULL,
                        /*crop_box*/NULL, /*error_cb*/NULL,
                        /*error_cbdata*/NULL);
  if (!pdf)
    return (false);

  // Create a Courier base font for the caption
  font = pdfioFileCreateFontObjFromBase(pdf, "Courier");

  if (!font)
  {
    pdfioFileClose(pdf);
    return (false);
  }

  // Create an image object from the JPEG/PNG image file...
  image = pdfioFileCreateImageObjFromFile(pdf, imagename, true);

  if (!image)
  {
    pdfioFileClose(pdf);
    return (false);
  }

  // Create a page dictionary with the font and image...
  dict = pdfioDictCreate(pdf);
  pdfioPageDictAddFont(dict, "F1", font);
  pdfioPageDictAddImage(dict, "IM1", image);

  // Create the page and its content stream...
  page = pdfioFileCreatePage(pdf, dict);

  // Position and scale the image on the page...
  width  = pdfioImageGetWidth(image);
  height = pdfioImageGetHeight(image);

  // Default media_box is "universal" 595.28x792 points (8.27x11in or
  // 210x279mm).  Use margins of 36 points (0.5in or 12.7mm) with another
  // 36 points for the caption underneath...
  swidth  = 595.28 - 72.0;
  sheight = swidth * height / width;
  if (sheight > (792.0 - 36.0 - 72.0))
  {
    sheight = 792.0 - 36.0 - 72.0;
    swidth  = sheight * width / height;
  }

  tx = 0.5 * (595.28 - swidth);
  ty = 0.5 * (792 - 36 - sheight);

  pdfioContentDrawImage(page, "IM1", tx, ty + 36.0, swidth, sheight);

  // Draw the caption in black...
  pdfioContentSetFillColorDeviceGray(page, 0.0);

  // Compute the starting point for the text - Courier is monospaced
  // with a nominal width of 0.6 times the text height...
  tx = 0.5 * (595.28 - 18.0 * 0.6 * strlen(caption));

  // Position and draw the caption underneath...
  pdfioContentTextBegin(page);
  pdfioContentSetTextFont(page, "F1", 18.0);
  pdfioContentTextMoveTo(page, tx, ty);
  pdfioContentTextShow(page, /*unicode*/false, caption);
  pdfioContentTextEnd(page);

  // Close the page stream and the PDF file...
  pdfioStreamClose(page);
  pdfioFileClose(pdf);

  return (true);
}

Generate a Code 128 Barcode

One-dimensional barcodes are often rendered using special fonts that map ASCII characters to sequences of bars that can be read. The examples directory contains such a font (code128.ttf) to create "Code 128" barcodes, with an accompanying bit of example code in code128.c.

The first thing you need to do is prepare the barcode string to use with the font. Each barcode begins with a start pattern followed by the characters or digits you want to encode, a weighted sum digit, and a stop pattern. The make_code128 function creates this string:

static char *                           // O - Output string
make_code128(char       *dst,           // I - Destination buffer
             const char *src,           // I - Source string
             size_t     dstsize)        // I - Size of destination buffer
{
  char          *dstptr,                // Pointer into destination buffer
                *dstend;                // End of destination buffer
  int           sum;                    // Weighted sum
  static const char *code128_chars =    // Code 128 characters
                " !\"#$%&'()*+,-./0123456789:;<=>?"
                "@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_"
                "`abcdefghijklmnopqrstuvwxyz{|}~\303"
                "\304\305\306\307\310\311\312";
  static const char code128_start_code_b = '\314';
                                        // Start code B
  static const char code128_stop = '\316';
                                        // Stop pattern


  // Start a Code B barcode...
  dstptr = dst;
  dstend = dst + dstsize - 3;

  *dstptr++ = code128_start_code_b;
  sum       = code128_start_code_b - 100;

  while (*src && dstptr < dstend)
  {
    if (*src >= ' ' && *src < 0x7f)
    {
      sum       += (dstptr - dst) * (*src - ' ');
      *dstptr++ = *src;
    }

    src ++;
  }

  // Add the weighted sum modulo 103
  *dstptr++ = code128_chars[sum % 103];

  // Add the stop pattern and return...
  *dstptr++ = code128_stop;
  *dstptr   = '\0';

  return (dst);
}

The main function does the rest of the work. The barcode font is imported using the pdfioFileCreateFontObjFromFile function. We pass false for the "unicode" argument since we just want the (default) ASCII encoding:

barcode_font = pdfioFileCreateFontObjFromFile(pdf, "code128.ttf",
                                              /*unicode*/false);

Since barcodes usually have the number or text represented by the barcode printed underneath it, we also need a regular text font, for which we can choose one of the standard 14 PostScript base fonts using the pdfioFIleCreateFontObjFromBase function:

text_font = pdfioFileCreateFontObjFromBase(pdf, "Helvetica");

Once we have these fonts we can measure the barcode and regular text labels using the pdfioContentTextMeasure function to determine how large the PDF page needs to be to hold the barcode and text:

// Compute sizes of the text...
const char *barcode = argv[1];
char barcode_temp[256];

if (!(barcode[0] & 0x80))
  barcode = make_code128(barcode_temp, barcode, sizeof(barcode_temp));

double barcode_height = 36.0;
double barcode_width =
    pdfioContentTextMeasure(barcode_font, barcode, barcode_height);

const char *text = argv[2];
double text_height = 0.0;
double text_width = 0.0;

if (text && text_font)
{
  text_height = 9.0;
  text_width  = pdfioContentTextMeasure(text_font, text,
                                        text_height);
}

// Compute the size of the PDF page...
pdfio_rect_t media_box;

media_box.x1 = 0.0;
media_box.y1 = 0.0;
media_box.x2 = (barcode_width > text_width ?
                    barcode_width : text_width) + 18.0;
media_box.y2 = barcode_height + text_height + 18.0;

Finally, we just need to create a page of the specified size that references the two fonts:

// Start a page for the barcode...
page_dict = pdfioDictCreate(pdf);

pdfioDictSetRect(page_dict, "MediaBox", &media_box);
pdfioDictSetRect(page_dict, "CropBox", &media_box);

pdfioPageDictAddFont(page_dict, "B128", barcode_font);
if (text_font)
  pdfioPageDictAddFont(page_dict, "TEXT", text_font);

page_st = pdfioFileCreatePage(pdf, page_dict);

With the barcode font called "B128" and the text font called "TEXT", we can use them to draw two strings:

// Draw the page...
pdfioContentSetFillColorGray(page_st, 0.0);

pdfioContentSetTextFont(page_st, "B128", barcode_height);
pdfioContentTextBegin(page_st);
pdfioContentTextMoveTo(page_st, 0.5 * (media_box.x2 - barcode_width),
                       9.0 + text_height);
pdfioContentTextShow(page_st, /*unicode*/false, barcode);
pdfioContentTextEnd(page_st);

if (text && text_font)
{
  pdfioContentSetTextFont(page_st, "TEXT", text_height);
  pdfioContentTextBegin(page_st);
  pdfioContentTextMoveTo(page_st, 0.5 * (media_box.x2 - text_width), 9.0);
  pdfioContentTextShow(page_st, /*unicode*/false, text);
  pdfioContentTextEnd(page_st);
}

pdfioStreamClose(page_st);

Convert Markdown to PDF

Markdown is a simple plain text format that supports things like headings, links, character styles, tables, and embedded images. The md2pdf.c example code uses the mmd library to convert markdown to a PDF file that can be distributed.

Note: The md2pdf example is by far the most complex example code included with PDFio and shows how to layout text, add headers and footers, add links, embed images, and format tables.