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Merged
merged 2 commits into from
Nov 4, 2015
Merged

Faster image generation in WebAgg/NbAgg backends #5389

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b3e9443
Faster image generation in WebAgg/NbAgg backends
mdboom Nov 3, 2015
bf1dca7
Add docstrings to _png.cpp
mdboom Nov 4, 2015
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18 changes: 4 additions & 14 deletions lib/matplotlib/backends/backend_webagg_core.py
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Original file line number Diff line number Diff line change
Expand Up @@ -143,11 +143,6 @@ class FigureCanvasWebAggCore(backend_agg.FigureCanvasAgg):
def __init__(self, *args, **kwargs):
backend_agg.FigureCanvasAgg.__init__(self, *args, **kwargs)

# A buffer to hold the PNG data for the last frame. This is
# retained so it can be resent to each client without
# regenerating it.
self._png_buffer = io.BytesIO()

# Set to True when the renderer contains data that is newer
# than the PNG buffer.
self._png_is_old = True
Expand Down Expand Up @@ -225,24 +220,19 @@ def get_diff_image(self):
diff = buff != last_buffer
output = np.where(diff, buff, 0)

# Clear out the PNG data buffer rather than recreating it
# each time. This reduces the number of memory
# (de)allocations.
self._png_buffer.truncate()
self._png_buffer.seek(0)

# TODO: We should write a new version of write_png that
# handles the differencing inline
_png.write_png(
buff = _png.write_png(
output.view(dtype=np.uint8).reshape(output.shape + (4,)),
self._png_buffer)
None, compression=6, filter=_png.PNG_FILTER_NONE)

# Swap the renderer frames
self._renderer, self._last_renderer = (
self._last_renderer, renderer)
self._force_full = False
self._png_is_old = False
return self._png_buffer.getvalue()

return buff

def get_renderer(self, cleared=None):
# Mirrors super.get_renderer, but caches the old one
Expand Down
139 changes: 130 additions & 9 deletions src/_png.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,27 @@ extern "C" {
#undef jmpbuf
#endif

struct buffer_t {
PyObject *str;
size_t cursor;
size_t size;
};


static void write_png_data_buffer(png_structp png_ptr, png_bytep data, png_size_t length)
{
buffer_t *buff = (buffer_t *)png_get_io_ptr(png_ptr);
if (buff->cursor + length < buff->size) {
memcpy(PyBytes_AS_STRING(buff->str) + buff->cursor, data, length);
buff->cursor += length;
}
}

static void flush_png_data_buffer(png_structp png_ptr)
{

}

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);
Expand Down Expand Up @@ -62,27 +83,66 @@ static void flush_png_data(png_structp png_ptr)
Py_XDECREF(result);
}

const char *Py_write_png__doc__ = "write_png(buffer, file, dpi=0)";
const char *Py_write_png__doc__ =
"write_png(buffer, file, dpi=0, compression=6, filter=auto)\n"
"\n"
"Parameters\n"
"----------\n"
"buffer : numpy array of image data\n"
" Must be an MxNxD array of dtype uint8.\n"
" - if D is 1, the image is greyscale\n"
" - if D is 3, the image is RGB\n"
" - if D is 4, the image is RGBA\n"
"\n"
"file : str path, file-like object or None\n"
" - If a str, must be a file path\n"
" - If a file-like object, must write bytes\n"
" - If None, a byte string containing the PNG data will be returned\n"
"\n"
"dpi : float\n"
" The dpi to store in the file metadata.\n"
"\n"
"compression : int\n"
" The level of lossless zlib compression to apply. 0 indicates no\n"
" compression. Values 1-9 indicate low/fast through high/slow\n"
" compression. Default is 6.\n"
"\n"
"filter : int\n"
" Filter to apply. Must be one of the constants: PNG_FILTER_NONE,\n"
" PNG_FILTER_SUB, PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH.\n"
" See the PNG standard for more information.\n"
" If not provided, libpng will try to automatically determine the\n"
" best filter on a line-by-line basis.\n"
"\n"
"Returns\n"
"-------\n"
"buffer : bytes or None\n"
" Byte string containing the PNG content if None was passed in for\n"
" file, otherwise None is returned.\n";

static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
{
numpy::array_view<unsigned char, 3> buffer;
PyObject *filein;
double dpi = 0;
const char *names[] = { "buffer", "file", "dpi", NULL };
int compression = 6;
int filter = -1;
const char *names[] = { "buffer", "file", "dpi", "compression", "filter", NULL };

// We don't need strict contiguity, just for each row to be
// contiguous, and libpng has special handling for getting RGB out
// of RGBA, ARGB or BGR. But the simplest thing to do is to
// enforce contiguity using array_view::converter_contiguous.
if (!PyArg_ParseTupleAndKeywords(args,
kwds,
"O&O|d:write_png",
"O&O|dii:write_png",
(char **)names,
&buffer.converter_contiguous,
&buffer,
&filein,
&dpi)) {
&dpi,
&compression,
&filter)) {
return NULL;
}

Expand All @@ -104,6 +164,8 @@ static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
png_infop info_ptr = NULL;
struct png_color_8_struct sig_bit;
int png_color_type;
buffer_t buff;
buff.str = NULL;

switch (channels) {
case 1:
Expand All @@ -122,6 +184,12 @@ static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
goto exit;
}

if (compression < 0 || compression > 9) {
PyErr_Format(PyExc_ValueError,
"compression must be in range 0-9, got %d", compression);
goto exit;
}

if (PyBytes_Check(filein) || PyUnicode_Check(filein)) {
if ((py_file = mpl_PyFile_OpenFile(filein, (char *)"wb")) == NULL) {
goto exit;
Expand All @@ -131,7 +199,14 @@ static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
py_file = filein;
}

if ((fp = mpl_PyFile_Dup(py_file, (char *)"wb", &offset))) {
if (filein == Py_None) {
buff.size = width * height * 4 + 1024;
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Presumably, this is large enough for uncompressed + PNG header and other overhead?

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Exactly.

buff.str = PyBytes_FromStringAndSize(NULL, buff.size);
if (buff.str == NULL) {
goto exit;
}
buff.cursor = 0;
} else if ((fp = mpl_PyFile_Dup(py_file, (char *)"wb", &offset))) {
close_dup_file = true;
} else {
PyErr_Clear();
Expand All @@ -152,6 +227,11 @@ static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
goto exit;
}

png_set_compression_level(png_ptr, compression);
if (filter >= 0) {
png_set_filter(png_ptr, 0, filter);
}

info_ptr = png_create_info_struct(png_ptr);
if (info_ptr == NULL) {
PyErr_SetString(PyExc_RuntimeError, "Could not create info struct");
Expand All @@ -163,7 +243,9 @@ static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
goto exit;
}

if (fp) {
if (buff.str) {
png_set_write_fn(png_ptr, (void *)&buff, &write_png_data_buffer, &flush_png_data_buffer);
} else if (fp) {
png_init_io(png_ptr, fp);
} else {
png_set_write_fn(png_ptr, (void *)py_file, &write_png_data, &flush_png_data);
Expand Down Expand Up @@ -227,8 +309,13 @@ static PyObject *Py_write_png(PyObject *self, PyObject *args, PyObject *kwds)
}

if (PyErr_Occurred()) {
Py_XDECREF(buff.str);
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Should you check that buff.str is not NULL?

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Py_XDECREF already does that (as opposed to Py_DECREF which does not).

return NULL;
} else {
if (buff.str) {
_PyBytes_Resize(&buff.str, buff.cursor);
return buff.str;
}
Py_RETURN_NONE;
}
}
Expand Down Expand Up @@ -494,21 +581,46 @@ static PyObject *_read_png(PyObject *filein, bool float_result)
}
}

const char *Py_read_png_float__doc__ = "read_png_float(file)";
const char *Py_read_png_float__doc__ =
"read_png_float(file)\n"
"\n"
"Read in a PNG file, converting values to floating-point doubles\n"
"in the range (0, 1)\n"
"\n"
"Parameters\n"
"----------\n"
"file : str path or file-like object\n";

static PyObject *Py_read_png_float(PyObject *self, PyObject *args, PyObject *kwds)
{
return _read_png(args, true);
}

const char *Py_read_png_int__doc__ = "read_png_int(file)";
const char *Py_read_png_int__doc__ =
"read_png_int(file)\n"
"\n"
"Read in a PNG file with original integer values.\n"
"\n"
"Parameters\n"
"----------\n"
"file : str path or file-like object\n";

static PyObject *Py_read_png_int(PyObject *self, PyObject *args, PyObject *kwds)
{
return _read_png(args, false);
}

const char *Py_read_png__doc__ = "read_png(file)";
const char *Py_read_png__doc__ =
"read_png(file)\n"
"\n"
"Read in a PNG file, converting values to floating-point doubles\n"
"in the range (0, 1)\n"
"\n"
"Alias for read_png_float()\n"
"\n"
"Parameters\n"
"----------\n"
"file : str path or file-like object\n";

static PyMethodDef module_methods[] = {
{"write_png", (PyCFunction)Py_write_png, METH_VARARGS|METH_KEYWORDS, Py_write_png__doc__},
Expand Down Expand Up @@ -558,6 +670,15 @@ extern "C" {

import_array();

if (PyModule_AddIntConstant(m, "PNG_FILTER_NONE", PNG_FILTER_NONE) ||
PyModule_AddIntConstant(m, "PNG_FILTER_SUB", PNG_FILTER_SUB) ||
PyModule_AddIntConstant(m, "PNG_FILTER_UP", PNG_FILTER_UP) ||
PyModule_AddIntConstant(m, "PNG_FILTER_AVG", PNG_FILTER_AVG) ||
PyModule_AddIntConstant(m, "PNG_FILTER_PAETH", PNG_FILTER_PAETH)) {
INITERROR;
}


#if PY3K
return m;
#endif
Expand Down