gstreamer/ext/gl/gstgldifferencematte.c

583 lines
19 KiB
C
Raw Normal View History

2014-03-16 10:23:16 +00:00
/*
* GStreamer
* Copyright (C) 2008 Filippo Argiolas <filippo.argiolas@gmail.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
/**
* SECTION:element-gldifferencematte.
* @title: gldifferencematte.
2014-03-16 10:23:16 +00:00
*
* Saves a background frame and replace it with a pixbuf.
*
* ## Examples
2014-03-16 10:23:16 +00:00
* |[
* gst-launch-1.0 videotestsrc ! glupload ! gldifferencemate location=backgroundimagefile ! glimagesink
2014-03-16 10:23:16 +00:00
* ]|
* FBO (Frame Buffer Object) and GLSL (OpenGL Shading Language) are required.
*
2014-03-16 10:23:16 +00:00
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <stdlib.h>
#include <png.h>
#include <gst/gl/gstglfuncs.h>
#include "gstglelements.h"
2014-03-16 10:23:16 +00:00
#include "gstgldifferencematte.h"
#include "effects/gstgleffectssources.h"
#if PNG_LIBPNG_VER >= 10400
#define int_p_NULL NULL
#define png_infopp_NULL NULL
#endif
#define GST_CAT_DEFAULT gst_gl_differencematte_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
#define DEBUG_INIT \
GST_DEBUG_CATEGORY_INIT (gst_gl_differencematte_debug, "gldifferencematte", 0, "gldifferencematte element");
#define gst_gl_differencematte_parent_class parent_class
2014-03-16 10:23:16 +00:00
G_DEFINE_TYPE_WITH_CODE (GstGLDifferenceMatte, gst_gl_differencematte,
GST_TYPE_GL_FILTER, DEBUG_INIT);
GST_ELEMENT_REGISTER_DEFINE_WITH_CODE (gldifferencematte, "gldifferencematte",
GST_RANK_NONE, GST_TYPE_GL_DIFFERENCEMATTE, gl_element_init (plugin));
2014-03-16 10:23:16 +00:00
static void gst_gl_differencematte_set_property (GObject * object,
guint prop_id, const GValue * value, GParamSpec * pspec);
static void gst_gl_differencematte_get_property (GObject * object,
guint prop_id, GValue * value, GParamSpec * pspec);
static gboolean gst_gl_differencematte_filter_texture (GstGLFilter * filter,
GstGLMemory * in_tex, GstGLMemory * out_tex);
2014-03-16 10:23:16 +00:00
static gboolean gst_gl_differencematte_loader (GstGLFilter * filter);
enum
{
PROP_0,
PROP_LOCATION,
};
/* init resources that need a gl context */
static gboolean
gst_gl_differencematte_gl_start (GstGLBaseFilter * base_filter)
2014-03-16 10:23:16 +00:00
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (base_filter);
GstGLFilter *filter = GST_GL_FILTER (base_filter);
GstGLContext *context = base_filter->context;
GstGLBaseMemoryAllocator *tex_alloc;
GstGLAllocationParams *params;
GError *error = NULL;
const gchar *frags[2];
2014-03-16 10:23:16 +00:00
gint i;
if (!GST_GL_BASE_FILTER_CLASS (parent_class)->gl_start (base_filter))
return FALSE;
tex_alloc = (GstGLBaseMemoryAllocator *)
gst_gl_memory_allocator_get_default (context);
params =
(GstGLAllocationParams *) gst_gl_video_allocation_params_new (context,
NULL, &filter->out_info, 0, NULL, GST_GL_TEXTURE_TARGET_2D, GST_GL_RGBA);
for (i = 0; i < 4; i++)
differencematte->midtexture[i] =
(GstGLMemory *) gst_gl_base_memory_alloc (tex_alloc, params);
gst_gl_allocation_params_free (params);
gst_object_unref (tex_alloc);
2016-03-17 12:50:00 +00:00
if (!(differencematte->identity_shader =
gst_gl_shader_new_default (context, &error))) {
GST_ELEMENT_ERROR (differencematte, RESOURCE, NOT_FOUND, ("%s",
"Failed to compile identity shader"), ("%s", error->message));
return FALSE;
2014-03-16 10:23:16 +00:00
}
frags[0] =
gst_gl_shader_string_get_highest_precision (context,
GST_GLSL_VERSION_NONE,
GST_GLSL_PROFILE_ES | GST_GLSL_PROFILE_COMPATIBILITY);
frags[1] = difference_fragment_source;
if (!(differencematte->shader[0] =
gst_gl_shader_new_link_with_stages (context, &error,
gst_glsl_stage_new_default_vertex (context),
gst_glsl_stage_new_with_strings (context, GL_FRAGMENT_SHADER,
2016-03-17 12:50:00 +00:00
GST_GLSL_VERSION_NONE,
GST_GLSL_PROFILE_ES | GST_GLSL_PROFILE_COMPATIBILITY, 2,
frags), NULL))) {
GST_ELEMENT_ERROR (differencematte, RESOURCE, NOT_FOUND, ("%s",
2016-03-17 12:50:00 +00:00
"Failed to compile difference shader"), ("%s", error->message));
return FALSE;
2014-03-16 10:23:16 +00:00
}
frags[1] = hconv7_fragment_source_gles2;
if (!(differencematte->shader[1] =
gst_gl_shader_new_link_with_stages (context, &error,
gst_glsl_stage_new_default_vertex (context),
gst_glsl_stage_new_with_strings (context, GL_FRAGMENT_SHADER,
2016-03-17 12:50:00 +00:00
GST_GLSL_VERSION_NONE,
GST_GLSL_PROFILE_ES | GST_GLSL_PROFILE_COMPATIBILITY, 2,
frags), NULL))) {
GST_ELEMENT_ERROR (differencematte, RESOURCE, NOT_FOUND, ("%s",
2016-03-17 12:50:00 +00:00
"Failed to compile convolution shader"), ("%s", error->message));
return FALSE;
2014-03-16 10:23:16 +00:00
}
frags[1] = vconv7_fragment_source_gles2;
if (!(differencematte->shader[2] =
gst_gl_shader_new_link_with_stages (context, &error,
gst_glsl_stage_new_default_vertex (context),
gst_glsl_stage_new_with_strings (context, GL_FRAGMENT_SHADER,
2016-03-17 12:50:00 +00:00
GST_GLSL_VERSION_NONE,
GST_GLSL_PROFILE_ES | GST_GLSL_PROFILE_COMPATIBILITY, 2,
frags), NULL))) {
GST_ELEMENT_ERROR (differencematte, RESOURCE, NOT_FOUND, ("%s",
2016-03-17 12:50:00 +00:00
"Failed to compile convolution shader"), ("%s", error->message));
return FALSE;
2014-03-16 10:23:16 +00:00
}
frags[1] = texture_interp_fragment_source;
if (!(differencematte->shader[3] =
gst_gl_shader_new_link_with_stages (context, &error,
gst_glsl_stage_new_default_vertex (context),
gst_glsl_stage_new_with_strings (context, GL_FRAGMENT_SHADER,
2016-03-17 12:50:00 +00:00
GST_GLSL_VERSION_NONE,
GST_GLSL_PROFILE_ES | GST_GLSL_PROFILE_COMPATIBILITY, 2,
frags), NULL))) {
GST_ELEMENT_ERROR (differencematte, RESOURCE, NOT_FOUND, ("%s",
2016-03-17 12:50:00 +00:00
"Failed to compile interpolation shader"), ("%s", error->message));
return FALSE;
2014-03-16 10:23:16 +00:00
}
/* FIXME: this should really be per shader */
filter->draw_attr_position_loc =
2016-03-17 12:50:00 +00:00
gst_gl_shader_get_attribute_location (differencematte->shader[2],
"a_position");
filter->draw_attr_texture_loc =
2016-03-17 12:50:00 +00:00
gst_gl_shader_get_attribute_location (differencematte->shader[2],
"a_texcoord");
return TRUE;
2014-03-16 10:23:16 +00:00
}
/* free resources that need a gl context */
static void
gst_gl_differencematte_gl_stop (GstGLBaseFilter * base_filter)
2014-03-16 10:23:16 +00:00
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (base_filter);
2014-03-16 10:23:16 +00:00
gint i;
if (differencematte->savedbgtexture) {
gst_memory_unref (GST_MEMORY_CAST (differencematte->savedbgtexture));
differencematte->savedbgtexture = NULL;
}
if (differencematte->newbgtexture) {
gst_memory_unref (GST_MEMORY_CAST (differencematte->newbgtexture));
differencematte->newbgtexture = NULL;
}
2014-03-16 10:23:16 +00:00
for (i = 0; i < 4; i++) {
2016-03-17 12:50:00 +00:00
if (differencematte->identity_shader) {
gst_object_unref (differencematte->identity_shader);
differencematte->identity_shader = NULL;
}
2014-03-16 10:23:16 +00:00
if (differencematte->shader[i]) {
gst_object_unref (differencematte->shader[i]);
differencematte->shader[i] = NULL;
}
2014-03-16 10:23:16 +00:00
if (differencematte->midtexture[i]) {
gst_memory_unref (GST_MEMORY_CAST (differencematte->midtexture[i]));
differencematte->midtexture[i] = NULL;
2014-03-16 10:23:16 +00:00
}
}
differencematte->location = NULL;
differencematte->pixbuf = NULL;
differencematte->bg_has_changed = FALSE;
GST_GL_BASE_FILTER_CLASS (parent_class)->gl_stop (base_filter);
2014-03-16 10:23:16 +00:00
}
static void
gst_gl_differencematte_class_init (GstGLDifferenceMatteClass * klass)
{
GObjectClass *gobject_class;
GstElementClass *element_class;
gobject_class = (GObjectClass *) klass;
element_class = GST_ELEMENT_CLASS (klass);
gst_gl_filter_add_rgba_pad_templates (GST_GL_FILTER_CLASS (klass));
2014-03-16 10:23:16 +00:00
gobject_class->set_property = gst_gl_differencematte_set_property;
gobject_class->get_property = gst_gl_differencematte_get_property;
GST_GL_BASE_FILTER_CLASS (klass)->gl_start = gst_gl_differencematte_gl_start;
GST_GL_BASE_FILTER_CLASS (klass)->gl_stop = gst_gl_differencematte_gl_stop;
2014-03-16 10:23:16 +00:00
GST_GL_FILTER_CLASS (klass)->filter_texture =
gst_gl_differencematte_filter_texture;
g_object_class_install_property (gobject_class,
PROP_LOCATION,
g_param_spec_string ("location",
"Background image location",
"Background image location", NULL,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
gst_element_class_set_metadata (element_class,
"Gstreamer OpenGL DifferenceMatte", "Filter/Effect/Video",
"Saves a background frame and replace it with a pixbuf",
"Filippo Argiolas <filippo.argiolas@gmail.com>");
GST_GL_BASE_FILTER_CLASS (klass)->supported_gl_api =
GST_GL_API_OPENGL | GST_GL_API_OPENGL3 | GST_GL_API_GLES2;
2014-03-16 10:23:16 +00:00
}
static void
gst_gl_differencematte_init (GstGLDifferenceMatte * differencematte)
{
differencematte->shader[0] = NULL;
differencematte->shader[1] = NULL;
differencematte->shader[2] = NULL;
differencematte->shader[3] = NULL;
differencematte->location = NULL;
differencematte->pixbuf = NULL;
differencematte->savedbgtexture = 0;
differencematte->newbgtexture = 0;
differencematte->bg_has_changed = FALSE;
fill_gaussian_kernel (differencematte->kernel, 7, 30.0);
}
static void
gst_gl_differencematte_set_property (GObject * object, guint prop_id,
const GValue * value, GParamSpec * pspec)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (object);
switch (prop_id) {
case PROP_LOCATION:
g_free (differencematte->location);
2014-03-16 10:23:16 +00:00
differencematte->bg_has_changed = TRUE;
differencematte->location = g_value_dup_string (value);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
static void
gst_gl_differencematte_get_property (GObject * object, guint prop_id,
GValue * value, GParamSpec * pspec)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (object);
switch (prop_id) {
case PROP_LOCATION:
g_value_set_string (value, differencematte->location);
break;
default:
G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
break;
}
}
static void
init_pixbuf_texture (GstGLDifferenceMatte * differencematte)
2014-03-16 10:23:16 +00:00
{
GstGLContext *context = GST_GL_BASE_FILTER (differencematte)->context;
GstGLFilter *filter = GST_GL_FILTER (differencematte);
GstGLBaseMemoryAllocator *tex_alloc;
GstGLAllocationParams *params;
GstVideoInfo v_info;
tex_alloc = (GstGLBaseMemoryAllocator *)
gst_gl_memory_allocator_get_default (context);
gst_video_info_set_format (&v_info, GST_VIDEO_FORMAT_RGBA,
differencematte->pbuf_width, differencematte->pbuf_height);
params =
(GstGLAllocationParams *) gst_gl_video_allocation_params_new (context,
NULL, &v_info, 0, NULL, GST_GL_TEXTURE_TARGET_2D, GST_GL_RGBA);
differencematte->newbgtexture =
(GstGLMemory *) gst_gl_base_memory_alloc (tex_alloc, params);
gst_gl_allocation_params_free (params);
if (differencematte->savedbgtexture == NULL) {
params =
(GstGLAllocationParams *) gst_gl_video_allocation_params_new (context,
NULL, &filter->out_info, 0, NULL, GST_GL_TEXTURE_TARGET_2D,
GST_GL_RGBA);
differencematte->savedbgtexture =
(GstGLMemory *) gst_gl_base_memory_alloc (tex_alloc, params);
gst_gl_allocation_params_free (params);
2014-03-16 10:23:16 +00:00
}
gst_object_unref (tex_alloc);
2014-03-16 10:23:16 +00:00
}
static gboolean
gst_gl_differencematte_diff (GstGLFilter * filter, GstGLMemory * in_tex,
2014-03-16 10:23:16 +00:00
gpointer stuff)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (filter);
const GstGLFuncs *gl = GST_GL_BASE_FILTER (filter)->context->gl_vtable;
2014-03-16 10:23:16 +00:00
gst_gl_shader_use (differencematte->shader[0]);
gl->ActiveTexture (GL_TEXTURE0);
gl->BindTexture (GL_TEXTURE_2D, gst_gl_memory_get_texture_id (in_tex));
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[0], "current", 0);
gl->ActiveTexture (GL_TEXTURE1);
gl->BindTexture (GL_TEXTURE_2D,
gst_gl_memory_get_texture_id (differencematte->savedbgtexture));
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[0], "saved", 1);
gst_gl_filter_draw_fullscreen_quad (filter);
return TRUE;
2014-03-16 10:23:16 +00:00
}
static gboolean
gst_gl_differencematte_hblur (GstGLFilter * filter, GstGLMemory * in_tex,
2014-03-16 10:23:16 +00:00
gpointer stuff)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (filter);
const GstGLFuncs *gl = GST_GL_BASE_FILTER (filter)->context->gl_vtable;
2014-03-16 10:23:16 +00:00
gst_gl_shader_use (differencematte->shader[1]);
gl->ActiveTexture (GL_TEXTURE0);
gl->BindTexture (GL_TEXTURE_2D, gst_gl_memory_get_texture_id (in_tex));
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[1], "tex", 0);
gst_gl_shader_set_uniform_1fv (differencematte->shader[1], "kernel", 7,
differencematte->kernel);
2016-03-17 12:50:00 +00:00
gst_gl_shader_set_uniform_1f (differencematte->shader[1], "gauss_width",
GST_VIDEO_INFO_WIDTH (&filter->out_info));
2014-03-16 10:23:16 +00:00
gst_gl_filter_draw_fullscreen_quad (filter);
return TRUE;
2014-03-16 10:23:16 +00:00
}
static gboolean
gst_gl_differencematte_vblur (GstGLFilter * filter, GstGLMemory * in_tex,
2014-03-16 10:23:16 +00:00
gpointer stuff)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (filter);
const GstGLFuncs *gl = GST_GL_BASE_FILTER (filter)->context->gl_vtable;
2014-03-16 10:23:16 +00:00
gst_gl_shader_use (differencematte->shader[2]);
gl->ActiveTexture (GL_TEXTURE0);
gl->BindTexture (GL_TEXTURE_2D, gst_gl_memory_get_texture_id (in_tex));
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[2], "tex", 0);
gst_gl_shader_set_uniform_1fv (differencematte->shader[2], "kernel", 7,
differencematte->kernel);
2016-03-17 12:50:00 +00:00
gst_gl_shader_set_uniform_1f (differencematte->shader[2], "gauss_height",
GST_VIDEO_INFO_HEIGHT (&filter->out_info));
2014-03-16 10:23:16 +00:00
gst_gl_filter_draw_fullscreen_quad (filter);
return TRUE;
2014-03-16 10:23:16 +00:00
}
static gboolean
gst_gl_differencematte_interp (GstGLFilter * filter, GstGLMemory * in_tex,
2014-03-16 10:23:16 +00:00
gpointer stuff)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (filter);
const GstGLFuncs *gl = GST_GL_BASE_FILTER (filter)->context->gl_vtable;
2014-03-16 10:23:16 +00:00
gst_gl_shader_use (differencematte->shader[3]);
gl->ActiveTexture (GL_TEXTURE0);
gl->BindTexture (GL_TEXTURE_2D, gst_gl_memory_get_texture_id (in_tex));
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[3], "blend", 0);
gl->ActiveTexture (GL_TEXTURE1);
gl->BindTexture (GL_TEXTURE_2D, differencematte->newbgtexture->tex_id);
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[3], "base", 1);
gl->ActiveTexture (GL_TEXTURE2);
gl->BindTexture (GL_TEXTURE_2D, differencematte->midtexture[2]->tex_id);
2014-03-16 10:23:16 +00:00
gst_gl_shader_set_uniform_1i (differencematte->shader[3], "alpha", 2);
gst_gl_filter_draw_fullscreen_quad (filter);
2014-03-16 10:23:16 +00:00
return TRUE;
2014-03-16 10:23:16 +00:00
}
static gboolean
gst_gl_differencematte_filter_texture (GstGLFilter * filter,
GstGLMemory * in_tex, GstGLMemory * out_tex)
2014-03-16 10:23:16 +00:00
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (filter);
differencematte->intexture = in_tex;
if (differencematte->bg_has_changed && (differencematte->location != NULL)) {
if (!gst_gl_differencematte_loader (filter))
differencematte->pixbuf = NULL;
init_pixbuf_texture (differencematte);
2014-03-16 10:23:16 +00:00
/* save current frame, needed to calculate difference between
* this frame and next ones */
gst_gl_filter_render_to_target_with_shader (filter, in_tex,
differencematte->savedbgtexture, differencematte->identity_shader);
2014-03-16 10:23:16 +00:00
if (differencematte->pixbuf) {
free (differencematte->pixbuf);
differencematte->pixbuf = NULL;
}
differencematte->bg_has_changed = FALSE;
}
if (differencematte->savedbgtexture != NULL) {
gst_gl_filter_render_to_target (filter, in_tex,
differencematte->midtexture[0], gst_gl_differencematte_diff, NULL);
gst_gl_filter_render_to_target (filter, differencematte->midtexture[0],
differencematte->midtexture[1], gst_gl_differencematte_hblur, NULL);
gst_gl_filter_render_to_target (filter, differencematte->midtexture[1],
differencematte->midtexture[2], gst_gl_differencematte_vblur, NULL);
gst_gl_filter_render_to_target (filter, in_tex, out_tex,
gst_gl_differencematte_interp, NULL);
2014-03-16 10:23:16 +00:00
} else {
gst_gl_filter_render_to_target_with_shader (filter, in_tex, out_tex,
differencematte->identity_shader);
2014-03-16 10:23:16 +00:00
}
return TRUE;
}
static void
user_warning_fn (png_structp png_ptr, png_const_charp warning_msg)
{
g_warning ("%s\n", warning_msg);
}
#define LOAD_ERROR(msg) { GST_WARNING ("unable to load %s: %s", differencematte->location, msg); return FALSE; }
static gboolean
gst_gl_differencematte_loader (GstGLFilter * filter)
{
GstGLDifferenceMatte *differencematte = GST_GL_DIFFERENCEMATTE (filter);
png_structp png_ptr;
png_infop info_ptr;
guint sig_read = 0;
png_uint_32 width = 0;
png_uint_32 height = 0;
gint bit_depth = 0;
gint color_type = 0;
gint interlace_type = 0;
png_FILE_p fp = NULL;
guint y = 0;
guchar **rows = NULL;
gint filler;
if (!GST_GL_BASE_FILTER (filter)->context)
2014-03-16 10:23:16 +00:00
return TRUE;
if ((fp = fopen (differencematte->location, "rb")) == NULL)
LOAD_ERROR ("file not found");
png_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (png_ptr == NULL) {
fclose (fp);
LOAD_ERROR ("failed to initialize the png_struct");
}
png_set_error_fn (png_ptr, NULL, NULL, user_warning_fn);
info_ptr = png_create_info_struct (png_ptr);
if (info_ptr == NULL) {
fclose (fp);
png_destroy_read_struct (&png_ptr, png_infopp_NULL, png_infopp_NULL);
LOAD_ERROR ("failed to initialize the memory for image information");
}
png_init_io (png_ptr, fp);
png_set_sig_bytes (png_ptr, sig_read);
png_read_info (png_ptr, info_ptr);
png_get_IHDR (png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
&interlace_type, int_p_NULL, int_p_NULL);
if (color_type == PNG_COLOR_TYPE_RGB) {
filler = 0xff;
png_set_filler (png_ptr, filler, PNG_FILLER_AFTER);
color_type = PNG_COLOR_TYPE_RGB_ALPHA;
}
if (color_type != PNG_COLOR_TYPE_RGB_ALPHA) {
fclose (fp);
png_destroy_read_struct (&png_ptr, png_infopp_NULL, png_infopp_NULL);
LOAD_ERROR ("color type is not rgb");
}
differencematte->pbuf_width = width;
differencematte->pbuf_height = height;
differencematte->pixbuf =
(guchar *) malloc (sizeof (guchar) * width * height * 4);
rows = (guchar **) malloc (sizeof (guchar *) * height);
for (y = 0; y < height; ++y)
rows[y] = (guchar *) (differencematte->pixbuf + y * width * 4);
png_read_image (png_ptr, rows);
free (rows);
png_read_end (png_ptr, info_ptr);
png_destroy_read_struct (&png_ptr, &info_ptr, png_infopp_NULL);
fclose (fp);
return TRUE;
}