[gnome-photos/wip/rishi/buffer-decoder: 7/12] Add PhotosGeglBufferCodecPng



commit bb5ed5e6ad6ccf1ce05e121a0c10f673fd5c226a
Author: Debarshi Ray <debarshir gnome org>
Date:   Sat Sep 8 01:02:14 2018 +0200

    Add PhotosGeglBufferCodecPng
    
    Bump minimum libpng version to 1.6.11.
    
    https://gitlab.gnome.org/GNOME/gnome-photos/issues/63

 configure.ac                       |   3 +-
 meson.build                        |   2 +-
 src/Makefile.am                    |   2 +
 src/meson.build                    |   1 +
 src/photos-gegl-buffer-codec-png.c | 948 +++++++++++++++++++++++++++++++++++++
 src/photos-gegl-buffer-codec-png.h |  39 ++
 src/photos-gegl.c                  |   2 +
 7 files changed, 995 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 0d448a4f..0428f43d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -51,6 +51,7 @@ GOA_MIN_VERSION=3.8.0
 GRILO_MIN_VERSION=0.3.5
 GTK_MIN_VERSION=3.22.16
 JPEG_MIN_VERSION=2.0.0
+PNG_MIN_VERSION=1.6.11
 
 G_LOG_DOMAIN=AC_PACKAGE_TARNAME
 AC_DEFINE_UNQUOTED([G_LOG_DOMAIN], ["$G_LOG_DOMAIN"], [Log domain])
@@ -105,7 +106,7 @@ PKG_CHECK_MODULES(GSETTINGS_DESKTOP_SCHEMAS, [gsettings-desktop-schemas])
 PKG_CHECK_MODULES(GTK, [gtk+-3.0 >= $GTK_MIN_VERSION])
 PKG_CHECK_MODULES(GTK_UNIX_PRINT, [gtk+-unix-print-3.0])
 PKG_CHECK_MODULES(JPEG, [libjpeg >= $JPEG_MIN_VERSION])
-PKG_CHECK_MODULES(PNG, [libpng16])
+PKG_CHECK_MODULES(PNG, [libpng16 >= $PNG_MIN_VERSION])
 PKG_CHECK_MODULES(TRACKER, [tracker-control-2.0 tracker-sparql-2.0])
 
 LIBGD_INIT([
diff --git a/meson.build b/meson.build
index e876dc68..4d025c64 100644
--- a/meson.build
+++ b/meson.build
@@ -170,7 +170,7 @@ libdazzle_dep = dependency('libdazzle-1.0', version: '>= 3.26.0')
 libgdata_dep = dependency('libgdata', version: '>= 0.15.2')
 libgfgraph_dep = dependency('libgfbgraph-0.2', version: '>= 0.2.1')
 libjpeg_dep = dependency('libjpeg', version: '>= 2.0.0')
-libpng_dep = dependency('libpng16')
+libpng_dep = dependency('libpng16', version: '>= 1.6.11')
 tracker_control_dep = dependency('tracker-control-2.0')
 tracker_sparql_dep = dependency('tracker-sparql-2.0')
 
diff --git a/src/Makefile.am b/src/Makefile.am
index c9c341f5..5387b52a 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -30,6 +30,8 @@ libgnome_photos_la_SOURCES = \
        photos-gegl-buffer-codec.h \
        photos-gegl-buffer-codec-jpeg.c \
        photos-gegl-buffer-codec-jpeg.h \
+       photos-gegl-buffer-codec-png.c \
+       photos-gegl-buffer-codec-png.h \
        photos-gegl-buffer-loader.c \
        photos-gegl-buffer-loader.h \
        photos-gegl-buffer-loader-builder.c \
diff --git a/src/meson.build b/src/meson.build
index 305767ab..71a0e2c9 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -6,6 +6,7 @@ sources = files(
   'photos-gegl.c',
   'photos-gegl-buffer-codec.c',
   'photos-gegl-buffer-codec-jpeg.c',
+  'photos-gegl-buffer-codec-png.c',
   'photos-gegl-buffer-loader.c',
   'photos-gegl-buffer-loader-builder.c',
   'photos-jpeg-count.c',
diff --git a/src/photos-gegl-buffer-codec-png.c b/src/photos-gegl-buffer-codec-png.c
new file mode 100644
index 00000000..95fd1ddf
--- /dev/null
+++ b/src/photos-gegl-buffer-codec-png.c
@@ -0,0 +1,948 @@
+/*
+ * Photos - access, organize and share your photos on GNOME
+ * Copyright © 1999 The Free Software Foundation
+ * Copyright © 1999 Mark Crichton
+ * Copyright © 2006 Øyvind Kolås
+ * Copyright © 2018 Red Hat, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* Based on code from:
+ *   + GdkPixbuf
+ *   + GEGL
+ */
+
+
+#include "config.h"
+
+#include <setjmp.h>
+
+#include <gegl.h>
+#include <glib.h>
+#include <glib/gi18n.h>
+#include <png.h>
+
+#include "photos-debug.h"
+#include "photos-error.h"
+#include "photos-gegl.h"
+#include "photos-gegl-buffer-codec-png.h"
+
+
+struct _PhotosGeglBufferCodecPng
+{
+  PhotosGeglBufferCodec parent_instance;
+  GError **error;
+  GeglBuffer *buffer;
+  GeglBuffer *buffer_original;
+  GeglBuffer *buffer_zoom_from_original;
+  GeglBufferMatrix2 inverse_jacobian;
+  GeglSampler *sampler;
+  gboolean can_set_size;
+  gboolean decoding;
+  gboolean fatal_error_occurred;
+  gboolean pending_zoom_from_original;
+  gdouble zoom_from_original_x;
+  gdouble zoom_from_original_y;
+  gint n_interlacing_passes;
+  gint original_height_needed_for_zoom;
+  gint scanline;
+  gint tile_height;
+  gint tile_stride;
+  gint tile_width;
+  gpointer line;
+  gpointer tile_memory;
+  guint stride_original;
+  png_infop png_info_ptr;
+  png_structp png_read_ptr;
+};
+
+enum
+{
+  PROP_0,
+  PROP_BUFFER,
+  PROP_CAN_SET_SIZE
+};
+
+
+G_DEFINE_TYPE_WITH_CODE (PhotosGeglBufferCodecPng, photos_gegl_buffer_codec_png, 
PHOTOS_TYPE_GEGL_BUFFER_CODEC,
+                         photos_gegl_ensure_extension_points ();
+                         g_io_extension_point_implement (PHOTOS_GEGL_BUFFER_CODEC_EXTENSION_POINT_NAME,
+                                                         g_define_type_id,
+                                                         "png",
+                                                         0));
+
+
+static const gchar *MIME_TYPES[] =
+{
+  "image/png",
+  NULL
+};
+
+
+static const Babl *
+photos_gegl_buffer_codec_png_get_format (const Babl *space, gint bit_depth, gint color_type, GError **error)
+{
+  const Babl *ret_val = NULL;
+  g_autoptr (GString) format_name_str = NULL;
+
+  g_return_val_if_fail (space != NULL, NULL);
+  g_return_val_if_fail (bit_depth == 8 || bit_depth == 16, NULL);
+  g_return_val_if_fail (error == NULL || *error == NULL, NULL);
+
+  format_name_str = g_string_new (NULL);
+
+  switch (color_type)
+    {
+    case PNG_COLOR_TYPE_GRAY:
+      g_string_append (format_name_str, "Y'");
+      break;
+
+    case PNG_COLOR_TYPE_GRAY_ALPHA:
+      g_string_append (format_name_str, "Y'A");
+      break;
+
+    case PNG_COLOR_TYPE_PALETTE:
+    case PNG_COLOR_TYPE_RGB:
+      g_string_append (format_name_str, "R'G'B'");
+      break;
+
+    case PNG_COLOR_TYPE_PALETTE | PNG_COLOR_MASK_ALPHA:
+    case PNG_COLOR_TYPE_RGB_ALPHA:
+      g_string_append (format_name_str, "R'G'B'A");
+      break;
+
+    default:
+      g_set_error (error, PHOTOS_ERROR, 0, _("Unsupported PNG color space: %d"), color_type);
+      goto out;
+      break;
+    }
+
+  g_string_append_c (format_name_str, ' ');
+
+  switch (bit_depth)
+    {
+    case 8:
+      g_string_append (format_name_str, "u8");
+      break;
+
+    case 16:
+      g_string_append (format_name_str, "u16");
+      break;
+
+    default:
+      g_assert_not_reached ();
+      break;
+    }
+
+  ret_val = babl_format_with_space (format_name_str->str, space);
+
+ out:
+  return ret_val;
+}
+
+
+static const Babl *
+photos_gegl_buffer_codec_png_get_space (png_structp png_read_ptr,
+                                        png_infop png_info_ptr,
+                                        gdouble *out_gamma,
+                                        GError **error)
+{
+  const Babl *ret_val = NULL;
+  const Babl *space = NULL;
+  const Babl *space_sRGB;
+  gdouble gamma = 0.45455;
+  gint icc_profile_compression_type;
+  png_bytep icc_profile = NULL;
+  png_charp icc_profile_name;
+  png_uint_32 has_gamma = 0;
+  png_uint_32 icc_profile_len;
+
+  g_return_val_if_fail (error == NULL || *error == NULL, NULL);
+
+  space_sRGB = babl_space ("sRGB");
+
+  has_gamma = png_get_valid (png_read_ptr, png_info_ptr, PNG_INFO_gAMA);
+  if (has_gamma != 0)
+    {
+      png_get_gAMA (png_read_ptr, png_info_ptr, &gamma);
+      if (gamma <= 0.0)
+        {
+          g_set_error (error, PHOTOS_ERROR, 0, _("Invalid gamma in PNG: %f"), gamma);
+          goto out;
+        }
+    }
+
+  png_get_iCCP (png_read_ptr,
+                png_info_ptr,
+                &icc_profile_name,
+                &icc_profile_compression_type,
+                &icc_profile,
+                &icc_profile_len);
+
+  if (icc_profile != NULL)
+    {
+      const gchar *error_message = NULL;
+
+      space = babl_space_from_icc ((char *) icc_profile,
+                                   (gint) icc_profile_len,
+                                   BABL_ICC_INTENT_RELATIVE_COLORIMETRIC,
+                                   &error_message);
+      if (space == NULL)
+        {
+          g_warning ("Unable to create Babl space from ICC profile: %s", error_message);
+          space = space_sRGB;
+        }
+    }
+
+  if (space == NULL)
+    {
+      png_uint_32 has_sRGB;
+
+      has_sRGB = png_get_valid (png_read_ptr, png_info_ptr, PNG_INFO_sRGB);
+      if (has_sRGB != 0)
+        space = space_sRGB;
+    }
+
+  if (space == NULL && has_gamma != 0)
+    {
+      const Babl *trc;
+      gdouble blue[2] = {0.1500, 0.0600}; /* default to sRGB */
+      gdouble green[2] = {0.3000, 0.6000}; /* default to sRGB */
+      gdouble red[2] = {0.6400, 0.3300}; /* default to sRGB */
+      gdouble white_point[2] = {0.3127, 0.3290}; /* default to sRGB */
+      png_uint_32 has_chromaticities = 0;
+
+      has_chromaticities = png_get_valid (png_read_ptr, png_info_ptr, PNG_INFO_cHRM);
+      if (has_chromaticities != 0)
+        {
+          png_get_cHRM (png_read_ptr,
+                        png_info_ptr,
+                        &white_point[0],
+                        &white_point[1],
+                        &red[0],
+                        &red[1],
+                        &green[0],
+                        &green[1],
+                        &blue[0],
+                        &blue[1]);
+        }
+
+      trc = babl_trc_gamma (1.0 / gamma);
+      space = babl_space_from_chromaticities (NULL,
+                                              white_point[0],
+                                              white_point[1],
+                                              red[0],
+                                              red[1],
+                                              green[0],
+                                              green[1],
+                                              blue[0],
+                                              blue[1],
+                                              trc,
+                                              trc,
+                                              trc,
+                                              BABL_SPACE_FLAG_EQUALIZE);
+    }
+
+  if (space == NULL)
+    space = space_sRGB;
+
+  if (out_gamma != NULL)
+    *out_gamma = gamma;
+
+  g_return_val_if_fail (space != NULL, NULL);
+  g_return_val_if_fail (gamma > 0.0, NULL);
+
+  ret_val = space;
+
+ out:
+  return ret_val;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_zoom_from_original (PhotosGeglBufferCodecPng *self)
+{
+  const Babl *format_original;
+  const Babl *format_zoom_from_original;
+  GeglRectangle bbox_tile;
+  gint buffer_width;
+  gint tile_row;
+
+  g_return_if_fail (self->buffer != self->buffer_original);
+  g_return_if_fail (self->buffer_zoom_from_original != self->buffer_original);
+  g_return_if_fail (self->pending_zoom_from_original);
+  g_return_if_fail (self->tile_memory != NULL);
+
+  format_original = gegl_buffer_get_format (self->buffer_original);
+  g_return_if_fail (format_original != NULL);
+
+  format_zoom_from_original = gegl_buffer_get_format (self->buffer_zoom_from_original);
+
+  bbox_tile.height = self->tile_height;
+  bbox_tile.width = self->tile_width;
+  bbox_tile.x = 0;
+
+  tile_row = (self->scanline - 1) / self->original_height_needed_for_zoom;
+  bbox_tile.y = tile_row * self->tile_height;
+
+  buffer_width = gegl_buffer_get_width (self->buffer_zoom_from_original);
+
+  if (G_APPROX_VALUE (self->zoom_from_original_x, self->zoom_from_original_y, PHOTOS_EPSILON))
+    {
+      g_return_if_fail (format_original == format_zoom_from_original);
+
+      for (bbox_tile.x = 0; bbox_tile.x < buffer_width; bbox_tile.x += self->tile_width)
+        {
+          gegl_buffer_get (self->buffer_original,
+                           &bbox_tile,
+                           self->zoom_from_original_x,
+                           format_original,
+                           self->tile_memory,
+                           self->tile_stride,
+                           GEGL_ABYSS_NONE | GEGL_BUFFER_FILTER_AUTO);
+
+          gegl_buffer_set (self->buffer_zoom_from_original,
+                           &bbox_tile,
+                           0,
+                           format_original,
+                           self->tile_memory,
+                           self->tile_stride);
+        }
+    }
+  else
+    {
+      GeglSamplerGetFun sampler_get_fun;
+      const gdouble u_base = self->inverse_jacobian.coeff[0][0] * 0.5;
+      const gdouble v_base = self->inverse_jacobian.coeff[1][1] * 0.5;
+      const gdouble v_tile = v_base + self->inverse_jacobian.coeff[1][1] * bbox_tile.y;
+      gint format_components;
+      gint j;
+      gint k;
+
+      sampler_get_fun = gegl_sampler_get_fun (self->sampler);
+      format_components = babl_format_get_n_components (format_zoom_from_original);
+
+      for (bbox_tile.x = 0; bbox_tile.x < buffer_width; bbox_tile.x += self->tile_width)
+        {
+          gdouble u_tile = u_base + self->inverse_jacobian.coeff[0][0] * bbox_tile.x;
+          gdouble v = v_tile;
+          gfloat *pixel = (gfloat *) self->tile_memory;
+
+          for (j = 0; j < self->tile_height; j++)
+            {
+              gdouble u = u_tile;
+
+              for (k = 0; k < self->tile_width; k++)
+                {
+                  sampler_get_fun (self->sampler, u, v, &self->inverse_jacobian, pixel, GEGL_ABYSS_NONE);
+                  pixel += format_components;
+                  u += self->inverse_jacobian.coeff[0][0];
+                }
+
+              v += self->inverse_jacobian.coeff[1][1];
+            }
+
+          gegl_buffer_set (self->buffer_zoom_from_original,
+                           &bbox_tile,
+                           0,
+                           format_zoom_from_original,
+                           self->tile_memory,
+                           self->tile_stride);
+        }
+    }
+}
+
+
+static void
+photos_gegl_buffer_codec_png_end (png_structp png_read_ptr, png_infop png_info_ptr)
+{
+  PhotosGeglBufferCodecPng *self;
+
+  self = PHOTOS_GEGL_BUFFER_CODEC_PNG (png_get_progressive_ptr (png_read_ptr));
+
+  if (self->fatal_error_occurred)
+    goto out;
+
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer));
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer_original));
+
+  if (self->buffer != self->buffer_original && self->pending_zoom_from_original)
+    {
+      photos_gegl_buffer_codec_png_zoom_from_original (self);
+      self->pending_zoom_from_original = FALSE;
+    }
+
+ out:
+  return;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_error (png_structp png_read_ptr, png_const_charp error_message)
+{
+  PhotosGeglBufferCodecPng *self;
+
+  self = PHOTOS_GEGL_BUFFER_CODEC_PNG (png_get_error_ptr (png_read_ptr));
+  self->fatal_error_occurred = TRUE;
+
+  /* Check for *error == NULL for robustness against crappy PNG
+   * library.
+   */
+  if (self->error && *self->error == NULL)
+    g_set_error (self->error, PHOTOS_ERROR, 0, _("Error reading PNG: %s"), error_message);
+
+  longjmp (png_jmpbuf (png_read_ptr), 1);
+  g_assert_not_reached ();
+}
+
+
+static void
+photos_gegl_buffer_codec_png_info (png_structp png_read_ptr, png_infop png_info_ptr)
+{
+  PhotosGeglBufferCodecPng *self;
+  const Babl *format_original = NULL;
+  const Babl *space = NULL;
+  const Babl *space_sRGB;
+  GeglRectangle bbox;
+  const gchar *format_name;
+  gdouble gamma;
+  gdouble target_height;
+  gdouble target_width;
+  gint bit_depth;
+  gint bpp_original;
+  gint color_type;
+  gint format_components;
+  gint interlace_type;
+  guint target_height_rounded;
+  guint target_width_rounded;
+  png_byte channels;
+  png_uint_32 has_transparency;
+  png_uint_32 height;
+  png_uint_32 width;
+
+  self = PHOTOS_GEGL_BUFFER_CODEC_PNG (png_get_progressive_ptr (png_read_ptr));
+
+  if (self->fatal_error_occurred)
+    goto out;
+
+  g_return_if_fail (self->buffer == NULL);
+  g_return_if_fail (self->buffer_original == NULL);
+  g_return_if_fail (self->line == NULL);
+
+  space_sRGB = babl_space ("sRGB");
+
+  png_get_IHDR (png_read_ptr, png_info_ptr, NULL, NULL, &bit_depth, &color_type, &interlace_type, NULL, 
NULL);
+
+  if (bit_depth < 8)
+    png_set_expand (png_read_ptr);
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+  else if (bit_depth == 16)
+    png_set_swap (png_read_ptr);
+#endif
+
+  if (color_type == PNG_COLOR_TYPE_PALETTE)
+    png_set_expand (png_read_ptr);
+
+  has_transparency = png_get_valid (png_read_ptr, png_info_ptr, PNG_INFO_tRNS);
+  if (has_transparency != 0)
+    png_set_expand (png_read_ptr);
+
+  self->n_interlacing_passes = png_set_interlace_handling (png_read_ptr);
+  g_return_if_fail ((interlace_type == PNG_INTERLACE_NONE && self->n_interlacing_passes == 1)
+                    || (interlace_type != PNG_INTERLACE_NONE && self->n_interlacing_passes > 1));
+
+  space = photos_gegl_buffer_codec_png_get_space (png_read_ptr, png_info_ptr, &gamma, self->error);
+  if (space == NULL)
+    {
+      self->fatal_error_occurred = TRUE;
+      goto out;
+    }
+
+  if (space == space_sRGB)
+    png_set_gamma (png_read_ptr, 2.2, gamma);
+
+  png_read_update_info (png_read_ptr, png_info_ptr);
+  png_get_IHDR (png_read_ptr, png_info_ptr, &width, &height, &bit_depth, &color_type, NULL, NULL, NULL);
+
+  g_return_if_fail (bit_depth == 8 || bit_depth == 16);
+
+  photos_debug (PHOTOS_DEBUG_GEGL, "GeglBufferCodecPng: Original size: %u×%u", (guint) width, (guint) 
height);
+  if (height == 0 || width == 0)
+    {
+      g_set_error (self->error, PHOTOS_ERROR, 0, _("Original PNG has zero width or height"));
+      self->fatal_error_occurred = TRUE;
+      goto out;
+    }
+
+  self->can_set_size = TRUE;
+  g_signal_emit_by_name (self, "size-prepared", (guint) width, (guint) height);
+  self->can_set_size = FALSE;
+
+  target_height = photos_gegl_buffer_codec_get_height (PHOTOS_GEGL_BUFFER_CODEC (self));
+  target_width = photos_gegl_buffer_codec_get_width (PHOTOS_GEGL_BUFFER_CODEC (self));
+
+  photos_debug (PHOTOS_DEBUG_GEGL, "GeglBufferCodecPng: Target size: %f×%f", target_width, target_height);
+
+  if (target_height <= 0 || target_width <= 0)
+    {
+      g_set_error (self->error, PHOTOS_ERROR, 0, _("Transformed PNG has invalid width or height"));
+      self->fatal_error_occurred = TRUE;
+      goto out;
+    }
+
+  target_height_rounded = (guint) (target_height + 0.5);
+  target_width_rounded = (guint) (target_width + 0.5);
+
+  photos_debug (PHOTOS_DEBUG_GEGL,
+                "GeglBufferCodecPng: Target size rounded: %u×%u",
+                target_width_rounded,
+                target_height_rounded);
+
+  format_original = photos_gegl_buffer_codec_png_get_format (space, bit_depth, color_type, self->error);
+  if (format_original == NULL)
+    {
+      self->fatal_error_occurred = TRUE;
+      goto out;
+    }
+
+  format_name = babl_get_name (format_original);
+  photos_debug (PHOTOS_DEBUG_GEGL, "GeglBufferCodecPng: Original format: %s", format_name);
+
+  format_components = babl_format_get_n_components (format_original);
+  channels = png_get_channels (png_read_ptr, png_info_ptr);
+  g_return_if_fail (format_components == (gint) channels);
+
+  bpp_original = babl_format_get_bytes_per_pixel (format_original);
+  g_return_if_fail (bpp_original == bit_depth * (gint) channels / 8);
+
+  gegl_rectangle_set (&bbox, 0, 0, (guint) width, (guint) height);
+  self->buffer_original = gegl_buffer_new (&bbox, format_original);
+
+  if ((guint) height == target_height_rounded && (guint) width == target_width_rounded)
+    {
+      self->buffer_zoom_from_original = g_object_ref (self->buffer_original);
+      self->buffer = g_object_ref (self->buffer_zoom_from_original);
+    }
+  else
+    {
+      const Babl *format_zoom_from_original = NULL;
+      gdouble aspect_ratio = (gdouble) width / (gdouble) height;
+      gdouble target_aspect_ratio = target_width / target_height;
+      gint bpp_zoom_from_original;
+
+      self->zoom_from_original_x = (gdouble) target_width_rounded / (gdouble) width;
+      self->zoom_from_original_y = (gdouble) target_height_rounded / (gdouble) height;
+
+      if (G_APPROX_VALUE (aspect_ratio, target_aspect_ratio, PHOTOS_EPSILON))
+        {
+          gint x;
+          gint y;
+          guint zoom_from_original_height;
+          guint zoom_from_original_width;
+
+          format_zoom_from_original = format_original;
+
+          self->zoom_from_original_x = MAX (self->zoom_from_original_x, self->zoom_from_original_y);
+          self->zoom_from_original_y = self->zoom_from_original_x;
+
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Keep aspect ratio: Zoom from original: %f×%f",
+                        self->zoom_from_original_x,
+                        self->zoom_from_original_y);
+
+          zoom_from_original_height = (guint) (self->zoom_from_original_y * (gdouble) height + 0.5);
+          zoom_from_original_width = (guint) (self->zoom_from_original_x * (gdouble) width + 0.5);
+
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Keep aspect ratio: Zoom from original size: %u×%u",
+                        zoom_from_original_width,
+                        zoom_from_original_height);
+
+          g_assert_cmpuint (zoom_from_original_height, >=, target_height_rounded);
+          g_assert_cmpuint (zoom_from_original_width, >=, target_width_rounded);
+
+          gegl_rectangle_set (&bbox, 0, 0, zoom_from_original_width, zoom_from_original_height);
+          self->buffer_zoom_from_original = gegl_buffer_new (&bbox, format_zoom_from_original);
+
+          x = (zoom_from_original_width - target_width_rounded) / 2;
+          y = (zoom_from_original_height - target_height_rounded) / 2;
+          gegl_rectangle_set (&bbox, x, y, target_width_rounded, target_height_rounded);
+          self->buffer = gegl_buffer_create_sub_buffer (self->buffer_zoom_from_original, &bbox);
+        }
+      else
+        {
+          format_zoom_from_original = babl_format_with_space ("RaGaBaA float", space);
+
+          gegl_rectangle_set (&bbox, 0, 0, target_width_rounded, target_height_rounded);
+          self->buffer_zoom_from_original = gegl_buffer_new (&bbox, format_zoom_from_original);
+          self->buffer = g_object_ref (self->buffer_zoom_from_original);
+
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Don't keep aspect ratio: Zoom from mipmap: %f×%f",
+                        self->zoom_from_original_x,
+                        self->zoom_from_original_y);
+
+          photos_gegl_inverse_jacobian_zoom (&self->inverse_jacobian,
+                                             self->zoom_from_original_x,
+                                             self->zoom_from_original_y);
+
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Don't keep aspect ratio: Inverse Jacobian: %f, %f",
+                        self->inverse_jacobian.coeff[0][0],
+                        self->inverse_jacobian.coeff[0][1]);
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Don't keep aspect ratio: Inverse Jacobian: %f, %f",
+                        self->inverse_jacobian.coeff[1][0],
+                        self->inverse_jacobian.coeff[1][1]);
+
+          self->sampler = gegl_buffer_sampler_new (self->buffer_original,
+                                                   format_zoom_from_original,
+                                                   GEGL_SAMPLER_LINEAR);
+        }
+
+      g_return_if_fail (format_zoom_from_original != NULL);
+      bpp_zoom_from_original = babl_format_get_bytes_per_pixel (format_zoom_from_original);
+
+      g_object_get (self->buffer_zoom_from_original,
+                    "tile-height", &self->tile_height,
+                    "tile-width", &self->tile_width,
+                    NULL);
+
+      self->tile_stride = bpp_zoom_from_original * self->tile_width;
+      self->tile_memory = g_malloc0_n (self->tile_height, self->tile_stride);
+
+      self->original_height_needed_for_zoom = (gint) ((gdouble) self->tile_height
+                                                      * (gdouble) height
+                                                      / (gdouble) target_height_rounded
+                                                      + 0.5);
+    }
+
+  g_object_notify (G_OBJECT (self), "buffer");
+
+  /* Row strides are represented as signed integers (ie. gint)
+   * in GEGL. Even though the output_width is an unsigned
+   * integer (ie. guint or JDIMENSION), it must be ensured
+   * that the row stride can fit into the expected signed
+   * integer type (ie. gint).
+   *
+   * The comparison is made using the same unsigned integer
+   * type to avoid triggering -Wsign-compare.
+   */
+  if (bpp_original > 0 && width > 0 && (guint) width > G_MAXINT / (guint) bpp_original)
+    {
+      g_set_error (self->error,
+                   PHOTOS_ERROR,
+                   0,
+                   _("Overflow calculating row stride: %d×%u"),
+                   bpp_original,
+                   (guint) width);
+      goto out;
+    }
+
+  self->stride_original = (guint) bpp_original * (guint) width;
+  self->line = g_malloc_n (width, bpp_original);
+
+ out:
+  return;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_row (png_structp png_read_ptr,
+                                  png_bytep new_row,
+                                  png_uint_32 row_num,
+                                  gint pass_num)
+{
+  PhotosGeglBufferCodecPng *self;
+  const Babl *format_original;
+  GeglRectangle bbox_scanline;
+  gint buffer_height;
+  gint buffer_width;
+
+  self = PHOTOS_GEGL_BUFFER_CODEC_PNG (png_get_progressive_ptr (png_read_ptr));
+
+  if (self->fatal_error_occurred)
+    goto out;
+
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer));
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer_original));
+  g_return_if_fail (pass_num >= 0);
+  g_return_if_fail (pass_num < self->n_interlacing_passes);
+
+  format_original = gegl_buffer_get_format (self->buffer_original);
+  g_return_if_fail (format_original != NULL);
+
+  buffer_height = gegl_buffer_get_height (self->buffer_original);
+  g_return_if_fail (buffer_height > 0);
+
+  buffer_width = gegl_buffer_get_width (self->buffer_original);
+  g_return_if_fail (buffer_width > 0);
+
+  self->scanline = (gint) row_num;
+  if (self->scanline >= buffer_height)
+    {
+      g_set_error (self->error, PHOTOS_ERROR, 0, _("PNG has too many rows"));
+      self->fatal_error_occurred = TRUE;
+      goto out;
+    }
+
+  gegl_rectangle_set (&bbox_scanline, 0, self->scanline, (guint) buffer_width, 1);
+
+  if (pass_num > 0)
+    {
+      gegl_buffer_get (self->buffer_original,
+                       &bbox_scanline,
+                       1.0,
+                       format_original,
+                       self->line,
+                       (gint) self->stride_original,
+                       GEGL_ABYSS_NONE);
+    }
+
+  png_progressive_combine_row (png_read_ptr, self->line, new_row);
+  gegl_buffer_set (self->buffer_original,
+                   &bbox_scanline,
+                   0,
+                   format_original,
+                   self->line,
+                   (gint) self->stride_original);
+
+  self->pending_zoom_from_original = TRUE;
+
+  self->scanline++;
+  if (self->buffer != self->buffer_original && self->scanline % self->original_height_needed_for_zoom == 0)
+    {
+      photos_gegl_buffer_codec_png_zoom_from_original (self);
+      self->pending_zoom_from_original = FALSE;
+    }
+
+ out:
+  return;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_warning (png_structp png_read_ptr, png_const_charp warning_msg)
+{
+}
+
+
+static GeglBuffer *
+photos_gegl_buffer_codec_png_get_buffer (PhotosGeglBufferCodec *codec)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (codec);
+  return self->buffer;
+}
+
+
+static gboolean
+photos_gegl_buffer_codec_png_load_begin (PhotosGeglBufferCodec *codec, GError **error)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (codec);
+
+  g_return_val_if_fail (!self->decoding, FALSE);
+
+  self->error = error;
+
+  self->png_read_ptr = png_create_read_struct (PNG_LIBPNG_VER_STRING,
+                                               self,
+                                               photos_gegl_buffer_codec_png_error,
+                                               photos_gegl_buffer_codec_png_warning);
+  if (self->png_read_ptr == NULL)
+    {
+      /* A failure here isn't supposed to call the error callback, but
+       * it doesn't hurt to be careful.
+       */
+      if (self->error && *self->error == NULL)
+        g_set_error (self->error, PHOTOS_ERROR, 0, _("Couldn’t allocate memory for loading PNG"));
+
+      self->decoding = FALSE;
+      goto out;
+    }
+
+  self->png_info_ptr = png_create_info_struct (self->png_read_ptr);
+  if (self->png_info_ptr == NULL)
+    {
+      /* A failure here isn't supposed to call the error callback, but
+       * it doesn't hurt to be careful.
+       */
+      if (self->error && *self->error == NULL)
+        g_set_error (self->error, PHOTOS_ERROR, 0, _("Couldn’t allocate memory for loading PNG"));
+
+      self->decoding = FALSE;
+      goto out;
+    }
+
+  /* See:
+   * https://bugzilla.gnome.org/show_bug.cgi?id=721135
+   * https://bugzilla.gnome.org/show_bug.cgi?id=765850
+   */
+  png_set_benign_errors (self->png_read_ptr, TRUE);
+  png_set_option (self->png_read_ptr, PNG_SKIP_sRGB_CHECK_PROFILE, PNG_OPTION_ON);
+
+  if (setjmp (png_jmpbuf (self->png_read_ptr)))
+    {
+      self->decoding = FALSE;
+      goto out;
+    }
+
+  png_set_progressive_read_fn (self->png_read_ptr,
+                               self,
+                               photos_gegl_buffer_codec_png_info,
+                               photos_gegl_buffer_codec_png_row,
+                               photos_gegl_buffer_codec_png_end);
+
+  self->decoding = TRUE;
+
+ out:
+  self->error = NULL;
+  return self->decoding;
+}
+
+
+static gboolean
+photos_gegl_buffer_codec_png_load_increment (PhotosGeglBufferCodec *codec,
+                                             const guchar *buf,
+                                             gsize count,
+                                             GError **error)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (codec);
+  gboolean ret_val = FALSE;
+
+  g_return_val_if_fail (self->decoding, FALSE);
+
+  self->error = error;
+  if (setjmp (png_jmpbuf (self->png_read_ptr)))
+    {
+      ret_val = FALSE;
+      goto out;
+    }
+
+  png_process_data (self->png_read_ptr, self->png_info_ptr, (guchar *) buf, count);
+  if (self->fatal_error_occurred)
+    {
+      ret_val = FALSE;
+      goto out;
+    }
+
+  ret_val = TRUE;
+
+ out:
+  self->error = NULL;
+  return ret_val;
+}
+
+
+static gboolean
+photos_gegl_buffer_codec_png_load_stop (PhotosGeglBufferCodec *codec, GError **error)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (codec);
+  gboolean ret_val = FALSE;
+
+  g_return_val_if_fail (self->decoding, FALSE);
+
+  /* FIXME: This thing needs to report errors if we have unused image
+   * data.
+   */
+
+  if (self->buffer == NULL)
+    {
+      g_set_error (error, PHOTOS_ERROR, 0, _("Premature end-of-file encountered"));
+      goto out;
+    }
+
+  ret_val = TRUE;
+
+ out:
+  self->decoding = FALSE;
+  return ret_val;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_dispose (GObject *object)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (object);
+
+  g_clear_object (&self->buffer);
+  g_clear_object (&self->buffer_original);
+  g_clear_object (&self->buffer_zoom_from_original);
+  g_clear_object (&self->sampler);
+
+  G_OBJECT_CLASS (photos_gegl_buffer_codec_png_parent_class)->dispose (object);
+}
+
+
+static void
+photos_gegl_buffer_codec_png_finalize (GObject *object)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (object);
+
+  g_free (self->line);
+  g_free (self->tile_memory);
+  png_destroy_read_struct (&self->png_read_ptr, &self->png_info_ptr, NULL);
+
+  G_OBJECT_CLASS (photos_gegl_buffer_codec_png_parent_class)->finalize (object);
+}
+
+
+static void
+photos_gegl_buffer_codec_png_get_property (GObject *object, guint prop_id, GValue *value, GParamSpec *pspec)
+{
+  PhotosGeglBufferCodecPng *self = PHOTOS_GEGL_BUFFER_CODEC_PNG (object);
+
+  switch (prop_id)
+    {
+    case PROP_BUFFER:
+      g_value_set_object (value, self->buffer);
+      break;
+
+    case PROP_CAN_SET_SIZE:
+      g_value_set_boolean (value, self->can_set_size);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+
+static void
+photos_gegl_buffer_codec_png_init (PhotosGeglBufferCodecPng *self)
+{
+}
+
+
+static void
+photos_gegl_buffer_codec_png_class_init (PhotosGeglBufferCodecPngClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  PhotosGeglBufferCodecClass *buffer_codec_class = PHOTOS_GEGL_BUFFER_CODEC_CLASS (class);
+
+  buffer_codec_class->mime_types = (GStrv) MIME_TYPES;
+
+  object_class->dispose = photos_gegl_buffer_codec_png_dispose;
+  object_class->finalize = photos_gegl_buffer_codec_png_finalize;
+  object_class->get_property = photos_gegl_buffer_codec_png_get_property;
+  buffer_codec_class->get_buffer = photos_gegl_buffer_codec_png_get_buffer;
+  buffer_codec_class->load_begin = photos_gegl_buffer_codec_png_load_begin;
+  buffer_codec_class->load_increment = photos_gegl_buffer_codec_png_load_increment;
+  buffer_codec_class->load_stop = photos_gegl_buffer_codec_png_load_stop;
+
+  g_object_class_override_property (object_class, PROP_BUFFER, "buffer");
+  g_object_class_override_property (object_class, PROP_CAN_SET_SIZE, "can-set-size");
+}
diff --git a/src/photos-gegl-buffer-codec-png.h b/src/photos-gegl-buffer-codec-png.h
new file mode 100644
index 00000000..08c8749b
--- /dev/null
+++ b/src/photos-gegl-buffer-codec-png.h
@@ -0,0 +1,39 @@
+/*
+ * Photos - access, organize and share your photos on GNOME
+ * Copyright © 2018 Red Hat, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* Based on code from:
+ *   + GdkPixbuf
+ */
+
+#ifndef PHOTOS_GEGL_BUFFER_CODEC_PNG_H
+#define PHOTOS_GEGL_BUFFER_CODEC_PNG_H
+
+#include "photos-gegl-buffer-codec.h"
+
+G_BEGIN_DECLS
+
+#define PHOTOS_TYPE_GEGL_BUFFER_CODEC_PNG (photos_gegl_buffer_codec_png_get_type ())
+G_DECLARE_FINAL_TYPE (PhotosGeglBufferCodecPng,
+                      photos_gegl_buffer_codec_png,
+                      PHOTOS,
+                      GEGL_BUFFER_CODEC_PNG,
+                      PhotosGeglBufferCodec);
+
+G_END_DECLS
+
+#endif /* PHOTOS_GEGL_BUFFER_CODEC_JPEG_H */
diff --git a/src/photos-gegl.c b/src/photos-gegl.c
index d287f0b7..f58f1bd9 100644
--- a/src/photos-gegl.c
+++ b/src/photos-gegl.c
@@ -27,6 +27,7 @@
 #include "photos-gegl.h"
 #include "photos-gegl-buffer-codec.h"
 #include "photos-gegl-buffer-codec-jpeg.h"
+#include "photos-gegl-buffer-codec-png.h"
 #include "photos-operation-insta-curve.h"
 #include "photos-operation-insta-filter.h"
 #include "photos-operation-insta-hefe.h"
@@ -605,6 +606,7 @@ photos_gegl_ensure_builtins (void)
   if (g_once_init_enter (&once_init_value))
     {
       g_type_ensure (PHOTOS_TYPE_GEGL_BUFFER_CODEC_JPEG);
+      g_type_ensure (PHOTOS_TYPE_GEGL_BUFFER_CODEC_PNG);
 
       g_type_ensure (PHOTOS_TYPE_OPERATION_INSTA_CURVE);
       g_type_ensure (PHOTOS_TYPE_OPERATION_INSTA_FILTER);


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