matplotlib Code

#include <png.h>

// To remove a gcc warning
#ifdef _POSIX_C_SOURCE
#undef _POSIX_C_SOURCE
#endif

// TODO: Un CXX-ify this module
#include "CXX/Extensions.hxx"
#include "numpy/arrayobject.h"
#include "mplutils.h"

// the extension module
class _png_module : public Py::ExtensionModule<_png_module>
{
public:
    _png_module()
            : Py::ExtensionModule<_png_module>("_png")
    {
        add_varargs_method("write_png", &_png_module::write_png,
                           "write_png(buffer, width, height, fileobj, dpi=None)");
        add_varargs_method("read_png", &_png_module::read_png,
                           "read_png(fileobj)");
        initialize("Module to write PNG files");
    }

    virtual ~_png_module() {}

private:
    Py::Object write_png(const Py::Tuple& args);
    Py::Object read_png(const Py::Tuple& args);
};

static void write_png_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    PyObject* py_file_obj = (PyObject*)png_get_io_ptr(png_ptr);
    PyObject* write_method = PyObject_GetAttrString(py_file_obj, "write");
    PyObject* result = NULL;
    if (write_method)
    {
        result = PyObject_CallFunction(write_method, (char *)"s#", data,
                                       length);
    }
    Py_XDECREF(write_method);
    Py_XDECREF(result);
}

static void flush_png_data(png_structp png_ptr)
{
    PyObject* py_file_obj = (PyObject*)png_get_io_ptr(png_ptr);
    PyObject* flush_method = PyObject_GetAttrString(py_file_obj, "flush");
    PyObject* result = NULL;
    if (flush_method)
    {
        result = PyObject_CallFunction(flush_method, (char *)"");
    }
    Py_XDECREF(flush_method);
    Py_XDECREF(result);
}

// this code is heavily adapted from the paint license, which is in
// the file paint.license (BSD compatible) included in this
// distribution.  TODO, add license file to MANIFEST.in and CVS
Py::Object _png_module::write_png(const Py::Tuple& args)
{
    args.verify_length(4, 5);

    FILE *fp = NULL;
    bool close_file = false;
    Py::Object buffer_obj = Py::Object(args[0]);
    PyObject* buffer = buffer_obj.ptr();
    if (!PyObject_CheckReadBuffer(buffer))
    {
        throw Py::TypeError("First argument must be an rgba buffer.");
    }

    const void* pixBufferPtr = NULL;
    Py_ssize_t pixBufferLength = 0;
    if (PyObject_AsReadBuffer(buffer, &pixBufferPtr, &pixBufferLength))
    {
        throw Py::ValueError("Couldn't get data from read buffer.");
    }

    png_byte* pixBuffer = (png_byte*)pixBufferPtr;
    int width = (int)Py::Int(args[1]);
    int height = (int)Py::Int(args[2]);

    if (pixBufferLength < width * height * 4)
    {
        throw Py::ValueError("Buffer and width, height don't seem to match.");
    }

    Py::Object py_fileobj = Py::Object(args[3]);
#if PY_MAJOR_VERSION >= 3
    int fd = PyObject_AsFileDescriptor(py_fileobj.ptr());
    PyErr_Clear();
#endif
    if (py_fileobj.isString())
    {
        std::string fileName = Py::String(py_fileobj);
        const char *file_name = fileName.c_str();
        if ((fp = fopen(file_name, "wb")) == NULL)
        {
            throw Py::RuntimeError(
                Printf("Could not open file %s", file_name).str());
        }
        close_file = true;
    }
#if PY_MAJOR_VERSION >= 3
    else if (fd != -1)
    {
        fp = fdopen(fd, "w");
    }
#else
    else if (PyFile_CheckExact(py_fileobj.ptr()))
    {
        fp = PyFile_AsFile(py_fileobj.ptr());
    }
#endif
    else
    {
        PyObject* write_method = PyObject_GetAttrString(
            py_fileobj.ptr(), "write");
        if (!(write_method && PyCallable_Check(write_method)))
        {
            Py_XDECREF(write_method);
            throw Py::TypeError(
                "Object does not appear to be a 8-bit string path or a Python file-like object");
        }
        Py_XDECREF(write_method);
    }

    png_bytep *row_pointers = NULL;
    png_structp png_ptr = NULL;
    png_infop info_ptr = NULL;

    try
    {
        struct png_color_8_struct sig_bit;
        png_uint_32 row;

        row_pointers = new png_bytep[height];
        for (row = 0; row < (png_uint_32)height; ++row)
        {
            row_pointers[row] = pixBuffer + row * width * 4;
        }

        png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
        if (png_ptr == NULL)
        {
            throw Py::RuntimeError("Could not create write struct");
        }

        info_ptr = png_create_info_struct(png_ptr);
        if (info_ptr == NULL)
        {
            throw Py::RuntimeError("Could not create info struct");
        }

        if (setjmp(png_ptr->jmpbuf))
        {
            throw Py::RuntimeError("Error building image");
        }

        if (fp)
        {
            png_init_io(png_ptr, fp);
        }
        else
        {
            png_set_write_fn(png_ptr, (void*)py_fileobj.ptr(),
                             &write_png_data, &flush_png_data);
        }
        png_set_IHDR(png_ptr, info_ptr,
                     width, height, 8,
                     PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
                     PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);

        // Save the dpi of the image in the file
        if (args.size() == 5)
        {
            double dpi = Py::Float(args[4]);
            size_t dots_per_meter = (size_t)(dpi / (2.54 / 100.0));
            png_set_pHYs(png_ptr, info_ptr, dots_per_meter, dots_per_meter, PNG_RESOLUTION_METER);
        }

        // this a a color image!
        sig_bit.gray = 0;
        sig_bit.red = 8;
        sig_bit.green = 8;
        sig_bit.blue = 8;
        /* if the image has an alpha channel then */
        sig_bit.alpha = 8;
        png_set_sBIT(png_ptr, info_ptr, &sig_bit);

        png_write_info(png_ptr, info_ptr);
        png_write_image(png_ptr, row_pointers);
        png_write_end(png_ptr, info_ptr);
    }
    catch (...)
    {
        if (png_ptr && info_ptr)
        {
            png_destroy_write_struct(&png_ptr, &info_ptr);
        }
        delete [] row_pointers;
        if (fp && close_file)
        {
            fclose(fp);
        }
        /* Changed calls to png_destroy_write_struct to follow
           http://www.libpng.org/pub/png/libpng-manual.txt.
           This ensures the info_ptr memory is released.
        */
        throw;
    }

    png_destroy_write_struct(&png_ptr, &info_ptr);
    delete [] row_pointers;
#if PY_MAJOR_VERSION >= 3
    if (fp)
    {
        fflush(fp);
    }
#endif
    if (fp && close_file)
    {
        fclose(fp);
    }

    return Py::Object();
}

static void _read_png_data(PyObject* py_file_obj, png_bytep data, png_size_t length)
{
    PyObject* read_method = PyObject_GetAttrString(py_file_obj, "read");
    PyObject* result = NULL;
    char *buffer;
    Py_ssize_t bufflen;
    if (read_method)
    {
        result = PyObject_CallFunction(read_method, (char *)"i", length);
    }
#if PY_MAJOR_VERSION >= 3
    PyObject* utf8_result = PyUnicode_AsUTF8String(result);
    if (PyBytes_AsStringAndSize(utf8_result, &buffer, &bufflen) == 0)
#else
    if (PyString_AsStringAndSize(result, &buffer, &bufflen) == 0)
#endif
    {
        if (bufflen == (Py_ssize_t)length)
        {
            memcpy(data, buffer, length);
        }
    }
    Py_XDECREF(read_method);
    Py_XDECREF(result);
}

static void read_png_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    PyObject* py_file_obj = (PyObject*)png_get_io_ptr(png_ptr);
    _read_png_data(py_file_obj, data, length);
}

Py::Object
_png_module::read_png(const Py::Tuple& args)
{

    args.verify_length(1);
    png_byte header[8];   // 8 is the maximum size that can be checked
    FILE* fp = NULL;
    bool close_file = false;

    Py::Object py_fileobj = Py::Object(args[0]);
#if PY_MAJOR_VERSION >= 3
    int fd = PyObject_AsFileDescriptor(py_fileobj.ptr());
    PyErr_Clear();
#endif

    if (py_fileobj.isString())
    {
        std::string fileName = Py::String(py_fileobj);
        const char *file_name = fileName.c_str();
        if ((fp = fopen(file_name, "rb")) == NULL)
        {
            throw Py::RuntimeError(
                Printf("Could not open file %s for reading", file_name).str());
        }
        close_file = true;
    }
#if PY_MAJOR_VERSION >= 3
    else if (fd != -1) {
        fp = fdopen(fd, "r");
    }
#else
    else if (PyFile_CheckExact(py_fileobj.ptr()))
    {
        fp = PyFile_AsFile(py_fileobj.ptr());
    }
#endif
    else
    {
        PyObject* read_method = PyObject_GetAttrString(py_fileobj.ptr(), "read");
        if (!(read_method && PyCallable_Check(read_method)))
        {
            Py_XDECREF(read_method);
            throw Py::TypeError("Object does not appear to be a 8-bit string path or a Python file-like object");
        }
        Py_XDECREF(read_method);
    }

    if (fp)
    {
        if (fread(header, 1, 8, fp) != 8)
        {
            throw Py::RuntimeError(
                "_image_module::readpng: error reading PNG header");
        }
    }
    else
    {
        _read_png_data(py_fileobj.ptr(), header, 8);
    }
    if (png_sig_cmp(header, 0, 8))
    {
        throw Py::RuntimeError(
            "_image_module::readpng: file not recognized as a PNG file");
    }

    /* initialize stuff */
    png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);

    if (!png_ptr)
    {
        throw Py::RuntimeError(
            "_image_module::readpng:  png_create_read_struct failed");
    }

    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
        throw Py::RuntimeError(
            "_image_module::readpng:  png_create_info_struct failed");
    }

    if (setjmp(png_jmpbuf(png_ptr)))
    {
        throw Py::RuntimeError(
            "_image_module::readpng:  error during init_io");
    }

    if (fp)
    {
        png_init_io(png_ptr, fp);
    }
    else
    {
        png_set_read_fn(png_ptr, (void*)py_fileobj.ptr(), &read_png_data);
    }
    png_set_sig_bytes(png_ptr, 8);
    png_read_info(png_ptr, info_ptr);

    png_uint_32 width = info_ptr->width;
    png_uint_32 height = info_ptr->height;

    int bit_depth = info_ptr->bit_depth;

    // Unpack 1, 2, and 4-bit images
    if (bit_depth < 8)
        png_set_packing(png_ptr);

    // If sig bits are set, shift data
    png_color_8p sig_bit;
    if ((info_ptr->color_type != PNG_COLOR_TYPE_PALETTE) &&
        png_get_sBIT(png_ptr, info_ptr, &sig_bit))
    {
        png_set_shift(png_ptr, sig_bit);
    }

    // Convert big endian to little
    if (bit_depth == 16)
    {
        png_set_swap(png_ptr);
    }

    // Convert palletes to full RGB
    if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
    {
        png_set_palette_to_rgb(png_ptr);
    }

    // If there's an alpha channel convert gray to RGB
    if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
    {
        png_set_gray_to_rgb(png_ptr);
    }

    png_set_interlace_handling(png_ptr);
    png_read_update_info(png_ptr, info_ptr);

    /* read file */
    if (setjmp(png_jmpbuf(png_ptr)))
    {
        throw Py::RuntimeError(
            "_image_module::readpng: error during read_image");
    }

    png_bytep *row_pointers = new png_bytep[height];
    png_uint_32 row;

    for (row = 0; row < height; row++)
    {
        row_pointers[row] = new png_byte[png_get_rowbytes(png_ptr,info_ptr)];
    }

    png_read_image(png_ptr, row_pointers);

    npy_intp dimensions[3];
    dimensions[0] = height;  //numrows
    dimensions[1] = width;   //numcols
    if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
    {
        dimensions[2] = 4;     //RGBA images
    }
    else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
    {
        dimensions[2] = 3;     //RGB images
    }
    else
    {
        dimensions[2] = 1;     //Greyscale images
    }
    //For gray, return an x by y array, not an x by y by 1
    int num_dims  = (info_ptr->color_type & PNG_COLOR_MASK_COLOR) ? 3 : 2;

    double max_value = (1 << ((bit_depth < 8) ? 8 : bit_depth)) - 1;
    PyArrayObject *A = (PyArrayObject *) PyArray_SimpleNew(
        num_dims, dimensions, PyArray_FLOAT);

    if (A == NULL)
    {
        throw Py::MemoryError("Could not allocate image array");
    }

    for (png_uint_32 y = 0; y < height; y++)
    {
        png_byte* row = row_pointers[y];
        for (png_uint_32 x = 0; x < width; x++)
        {
            size_t offset = y * A->strides[0] + x * A->strides[1];
            if (bit_depth == 16)
            {
                png_uint_16* ptr = &reinterpret_cast<png_uint_16*>(row)[x * dimensions[2]];
                for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
                {
                    *(float*)(A->data + offset + p*A->strides[2]) = (float)(ptr[p]) / max_value;
                }
            }
            else
            {
                png_byte* ptr = &(row[x * dimensions[2]]);
                for (png_uint_32 p = 0; p < (png_uint_32)dimensions[2]; p++)
                {
                    *(float*)(A->data + offset + p*A->strides[2]) = (float)(ptr[p]) / max_value;
                }
            }
        }
    }

    //free the png memory
    png_read_end(png_ptr, info_ptr);
#ifndef png_infopp_NULL
    png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
#else
    png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);
#endif
    if (close_file)
    {
        fclose(fp);
    }
    for (row = 0; row < height; row++)
    {
        delete [] row_pointers[row];
    }
    delete [] row_pointers;
    return Py::asObject((PyObject*)A);
}

extern "C"
#if PY_MAJOR_VERSION >= 3
PyMODINIT_FUNC
PyInit__png(void)
#else
PyMODINIT_FUNC
init_png(void)
#endif
{
    import_array();

    static _png_module* _png = NULL;
    _png = new _png_module;

#if PY_MAJOR_VERSION >= 3
    return _png->module().ptr();
#endif
}