[gnome-photos/wip/rishi/buffer-decoder: 1/4] Add PhotosGeglBufferCodecPng

[Debarshi Ray <debarshir src gnome org>]

commit b9a3f43c25de3ea3d64ac621118eab338773f530
Author: Debarshi Ray <debarshir gnome org>
Date:   Sat Sep 8 01:02:14 2018 +0200

    Add PhotosGeglBufferCodecPng
    
    https://gitlab.gnome.org/GNOME/gnome-photos/issues/63

 src/photos-gegl-buffer-codec-png.c | 1006 ++++++++++++++++++++++++++++++++++++
 src/photos-gegl-buffer-codec-png.h |   39 ++
 2 files changed, 1045 insertions(+)
---
diff --git a/src/photos-gegl-buffer-codec-png.c b/src/photos-gegl-buffer-codec-png.c
new file mode 100644
index 00000000..af8e1a1d
--- /dev/null
+++ b/src/photos-gegl-buffer-codec-png.c
@@ -0,0 +1,1006 @@
+g/*
+ * Photos - access, organize and share your photos on GNOME
+ * Copyright © 1999 The Free Software Foundation
+ * Copyright © 1999 Mark Crichton
+ * 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 <gegl.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;
+  gboolean fatal_error_occurred;
+  gint first_pass_seen_in_chunk;
+  gint first_row_seen_in_chunk;
+  gint last_pass_seen_in_chunk;
+  gint last_row_seen_in_chunk;
+  gint max_row_seen_in_chunk;
+  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 gchar *
+photos_gegl_buffer_codec_png_get_colorspace_name (J_COLOR_SPACE png_color_space)
+{
+  const gchar *ret_val = NULL;
+
+  switch (png_color_space)
+    {
+    case JCS_UNKNOWN:
+      ret_val = "UNKNOWN";
+      break;
+
+    case JCS_CMYK:
+      ret_val = "CMYK";
+      break;
+
+    case JCS_GRAYSCALE:
+      ret_val = "GRAYSCALE";
+      break;
+
+    case JCS_RGB:
+      ret_val = "RGB";
+      break;
+
+    case JCS_YCbCr:
+      ret_val = "YCbCr";
+      break;
+
+    case JCS_YCCK:
+      ret_val = "YCCK";
+      break;
+
+    case JCS_EXT_ARGB:
+    case JCS_EXT_ABGR:
+    case JCS_EXT_BGR:
+    case JCS_EXT_BGRA:
+    case JCS_EXT_BGRX:
+    case JCS_EXT_RGB:
+    case JCS_EXT_RGBA:
+    case JCS_EXT_RGBX:
+    case JCS_EXT_XBGR:
+    case JCS_EXT_XRGB:
+    case JCS_RGB565:
+    default:
+      ret_val = "invalid";
+      break;
+    }
+
+  return ret_val;
+}
+
+
+static const Babl *
+photos_gegl_buffer_codec_png_get_format (J_COLOR_SPACE png_color_space,
+                                          JOCTET *icc_profile,
+                                          guint icc_profile_len)
+{
+  const Babl *format = NULL;
+  const Babl *ret_val = NULL;
+  const Babl *space = NULL;
+  const Babl *type;
+  const Babl *type_u8;
+
+  type_u8 = babl_type ("u8");
+
+  if (icc_profile != NULL)
+    {
+      const gchar *error_message = NULL;
+
+      space = babl_space_from_icc ((gchar *) 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);
+    }
+
+  switch (png_color_space)
+    {
+    case JCS_CMYK:
+      format = babl_format_with_space ("CMYK u8", space);
+      break;
+
+    case JCS_GRAYSCALE:
+      format = babl_format_with_space ("Y' u8", space);
+      break;
+
+    case JCS_RGB:
+      format = babl_format_with_space ("R'G'B' u8", space);
+      break;
+
+    case JCS_YCbCr:
+    case JCS_YCCK:
+    case JCS_EXT_ARGB:
+    case JCS_EXT_ABGR:
+    case JCS_EXT_BGR:
+    case JCS_EXT_BGRA:
+    case JCS_EXT_BGRX:
+    case JCS_EXT_RGB:
+    case JCS_EXT_RGBA:
+    case JCS_EXT_RGBX:
+    case JCS_EXT_XBGR:
+    case JCS_EXT_XRGB:
+    case JCS_RGB565:
+    case JCS_UNKNOWN:
+    default:
+      goto out;
+      break;
+    }
+
+  type = babl_format_get_type (format, 0);
+  g_return_val_if_fail (type == type_u8, NULL);
+
+  ret_val = format;
+
+ out:
+  return ret_val;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_error_exit (j_common_ptr cinfo)
+{
+  PhotosPngErrorMgr *jerr = (PhotosPngErrorMgr *) cinfo->err;
+  gchar buffer[JMSG_LENGTH_MAX];
+
+  cinfo->err->format_message (cinfo, buffer);
+
+  /* Check for *error == NULL for robustness against crappy PNG
+   * library.
+   */
+  if (jerr->error && *jerr->error == NULL)
+    g_set_error (jerr->error, PHOTOS_ERROR, 0, _("Error interpreting PNG image file (%s)"), buffer);
+
+  siglongjmp (jerr->setjmp_buffer, 1);
+  g_assert_not_reached ();
+}
+
+
+static gboolean
+photos_gegl_buffer_codec_png_fill_input_buffer (j_decompress_ptr cinfo)
+{
+  return FALSE;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_init_source (j_decompress_ptr cinfo)
+{
+  PhotosPngSourceMgr *src = (PhotosPngSourceMgr *) cinfo->src;
+  src->skip_next = 0;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_output_message (j_common_ptr cinfo)
+{
+}
+
+
+static void
+photos_gegl_buffer_codec_png_skip_input_data (j_decompress_ptr cinfo, glong num_bytes)
+{
+  PhotosPngSourceMgr *src = (PhotosPngSourceMgr *) cinfo->src;
+  glong num_can_do;
+
+  if (num_bytes > 0)
+    {
+      num_can_do = MIN (src->pub.bytes_in_buffer, (gsize) num_bytes);
+      src->pub.next_input_byte += (gsize) num_can_do;
+      src->pub.bytes_in_buffer -= (gsize) num_can_do;
+      src->skip_next = (gsize) (num_bytes - num_can_do);
+    }
+}
+
+
+static void
+photos_gegl_buffer_codec_png_term_source (j_decompress_ptr cinfo)
+{
+}
+
+
+static void
+photos_gegl_buffer_codec_png_zoom_from_mipmap (PhotosGeglBufferCodecPng *self)
+{
+  const Babl *format;
+  const Babl *format_mipmap;
+  GeglRectangle bbox_tile;
+  gint buffer_width;
+  gint tile_row;
+
+  g_return_if_fail (self->buffer != self->buffer_mipmap);
+  g_return_if_fail (self->buffer_zoom_from_mipmap != self->buffer_mipmap);
+  g_return_if_fail (self->pending_zoom_from_mipmap);
+
+  format = gegl_buffer_get_format (self->buffer);
+  g_return_if_fail (format != NULL);
+
+  format_mipmap = gegl_buffer_get_format (self->buffer_mipmap);
+  g_return_if_fail (format == format_mipmap);
+
+  bbox_tile.height = self->tile_height;
+  bbox_tile.width = self->tile_width;
+  bbox_tile.x = 0;
+
+  tile_row = (self->scanline - 1) / self->mipmap_height_needed_for_zoom;
+  bbox_tile.y = tile_row * self->tile_height;
+
+  buffer_width = gegl_buffer_get_width (self->buffer_zoom_from_mipmap);
+
+  if (G_APPROX_VALUE (self->zoom_from_mipmap_x, self->zoom_from_mipmap_y, PHOTOS_EPSILON))
+    {
+      for (bbox_tile.x = 0; bbox_tile.x < buffer_width; bbox_tile.x += self->tile_width)
+        {
+          gegl_buffer_get (self->buffer_mipmap,
+                           &bbox_tile,
+                           self->zoom_from_mipmap_x,
+                           format,
+                           self->tile_memory,
+                           self->tile_stride,
+                           GEGL_ABYSS_NONE | GEGL_BUFFER_FILTER_AUTO);
+
+          gegl_buffer_set (self->buffer_zoom_from_mipmap,
+                           &bbox_tile,
+                           0,
+                           format,
+                           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 bpp;
+      gint j;
+      gint k;
+
+      sampler_get_fun = gegl_sampler_get_fun (self->sampler);
+      bpp = babl_format_get_bytes_per_pixel (format);
+
+      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;
+          guchar *tile_memory = (guchar *) 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, tile_memory, 
GEGL_ABYSS_NONE);
+                  tile_memory += bpp;
+                  u += self->inverse_jacobian.coeff[0][0];
+                }
+
+              v += self->inverse_jacobian.coeff[1][1];
+            }
+
+          gegl_buffer_set (self->buffer_zoom_from_mipmap,
+                           &bbox_tile,
+                           0,
+                           format,
+                           self->tile_memory,
+                           self->tile_stride);
+        }
+    }
+}
+
+
+static gboolean
+photos_gegl_buffer_codec_png_load_lines (PhotosGeglBufferCodecPng *self, GError **error)
+{
+  const Babl *cmyk_u8;
+  const Babl *format;
+  GeglRectangle bbox_scanline;
+
+  cmyk_u8 = babl_format ("CMYK u8");
+  format = gegl_buffer_get_format (self->buffer_mipmap);
+
+  gegl_rectangle_set (&bbox_scanline, 0, self->scanline, (guint) self->cinfo.output_width, 1);
+
+  while (self->cinfo.output_scanline < self->cinfo.output_height)
+    {
+      JDIMENSION i;
+      JDIMENSION num_lines;
+
+      num_lines = png_read_scanlines (&self->cinfo, self->lines, self->cinfo.rec_outbuf_height);
+      if (num_lines == 0)
+        break;
+
+      for (i = 0; i < num_lines; i++)
+        {
+          /* Assume that all CMYK PNG files use inverted CMYK, as
+           * Photoshop does. See:
+           * https://bugzilla.gnome.org/show_bug.cgi?id=618096
+           * https://bugzilla.mozilla.org/show_bug.cgi?id=674619
+           */
+          if (format == cmyk_u8)
+            {
+              JDIMENSION j;
+
+              for (j = 0; j < self->stride_mipmap; j++)
+                self->lines[i][j] = 255 - self->lines[i][j];
+            }
+
+          gegl_buffer_set (self->buffer_mipmap, &bbox_scanline, 0, format, self->lines[i], 
GEGL_AUTO_ROWSTRIDE);
+          self->pending_zoom_from_mipmap = TRUE;
+
+          self->scanline++;
+          bbox_scanline.y = self->scanline;
+
+          if (self->buffer != self->buffer_mipmap && self->scanline % self->mipmap_height_needed_for_zoom == 
0)
+            {
+              photos_gegl_buffer_codec_png_zoom_from_mipmap (self);
+              self->pending_zoom_from_mipmap = FALSE;
+            }
+        }
+    }
+
+  if (self->buffer != self->buffer_mipmap
+      && self->cinfo.output_scanline >= self->cinfo.output_height
+      && self->pending_zoom_from_mipmap)
+    {
+      photos_gegl_buffer_codec_png_zoom_from_mipmap (self);
+      self->pending_zoom_from_mipmap = FALSE;
+    }
+
+  return TRUE;
+}
+
+
+static void
+photos_gegl_buffer_codec_png_parse_exif_app1 (PhotosGeglBufferCodecPng *self, png_saved_marker_ptr marker)
+{
+}
+
+
+static void
+photos_gegl_buffer_codec_png_parse_exif (PhotosGeglBufferCodecPng *self)
+{
+  png_saved_marker_ptr marker;
+
+  for (marker = self->cinfo.marker_list; marker != NULL; marker = marker->next)
+    {
+      if (marker->marker == PNG_APP0 + 1)
+        photos_gegl_buffer_codec_png_parse_exif_app1 (self, marker);
+    }
+}
+
+
+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->fatal_error_occurred = FALSE;
+  self->first_pass_seen_in_chunk = -1;
+  self->first_row_seen_in_chunk = -1;
+  self->last_pass_seen_in_chunk = -1;
+  self->last_row_seen_in_chunk = -1;
+  self->max_row_seen_in_chunk = -1;
+
+  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 (sigsetjmp (self->jerr.setjmp_buffer, 1))
+    {
+      png_destroy_decompress (&self->cinfo);
+      self->decoding = FALSE;
+      goto out;
+    }
+
+  png_create_decompress (&self->cinfo);
+  self->decoding = TRUE;
+
+  self->cinfo.src = (struct png_source_mgr *) &self->src;
+  self->src.pub.init_source = photos_gegl_buffer_codec_png_init_source;
+  self->src.pub.fill_input_buffer = photos_gegl_buffer_codec_png_fill_input_buffer;
+  self->src.pub.skip_input_data = photos_gegl_buffer_codec_png_skip_input_data;
+  self->src.pub.resync_to_restart = png_resync_to_restart;
+  self->src.pub.term_source = photos_gegl_buffer_codec_png_term_source;
+
+  self->jerr.error = NULL;
+
+  g_return_val_if_fail (self->decoding, FALSE);
+
+ out:
+  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 first;
+  gboolean ret_val = FALSE;
+  gsize last_bytes_left;
+  gsize last_num_left;
+  gsize num_left;
+  guint spinguard;
+  const guchar *bufhd;
+
+  g_return_val_if_fail (self->decoding, FALSE);
+
+  self->jerr.error = error;
+
+  if (sigsetjmp (self->jerr.setjmp_buffer, 1))
+    {
+      ret_val = FALSE;
+      goto out;
+    }
+
+  if (self->src_initialized && self->src.skip_next > 0)
+    {
+      if (self->src.skip_next > count)
+        {
+          self->src.skip_next -= count;
+          ret_val = TRUE;
+          goto out;
+        }
+
+      num_left = count - self->src.skip_next;
+      bufhd = buf + self->src.skip_next;
+      self->src.skip_next = 0;
+    }
+  else
+    {
+      num_left = count;
+      bufhd = buf;
+    }
+
+  if (num_left == 0)
+    {
+      ret_val = TRUE;
+      goto out;
+    }
+
+  last_num_left = num_left;
+  last_bytes_left = 0;
+  spinguard = 0;
+  first = TRUE;
+
+  while (TRUE)
+    {
+      if (num_left > 0)
+        {
+          gsize num_copy;
+
+          if (self->src.pub.bytes_in_buffer > 0 && self->src.pub.next_input_byte != self->src.buffer)
+            memmove (self->src.buffer, self->src.pub.next_input_byte, self->src.pub.bytes_in_buffer);
+
+          num_copy = MIN (SOURCE_BUF_SIZE - self->src.pub.bytes_in_buffer, num_left);
+          memcpy (self->src.buffer + self->src.pub.bytes_in_buffer, bufhd, num_copy);
+          self->src.pub.next_input_byte = self->src.buffer;
+          self->src.pub.bytes_in_buffer += num_copy;
+          bufhd += num_copy;
+          num_left -= num_copy;
+        }
+
+      if (first)
+        {
+          last_bytes_left = self->src.pub.bytes_in_buffer;
+          first = FALSE;
+        }
+      else if (self->src.pub.bytes_in_buffer == last_bytes_left && num_left == last_num_left)
+        {
+          spinguard++;
+        }
+      else
+        {
+          last_bytes_left = self->src.pub.bytes_in_buffer;
+          last_num_left = num_left;
+        }
+
+      if (spinguard > 2)
+        {
+          ret_val = TRUE;
+          goto out;
+        }
+
+      if (!self->got_header)
+        {
+          const Babl *format = NULL;
+          GeglRectangle bbox;
+          g_autofree JOCTET *icc_profile = NULL;
+          gdouble target_height;
+          gdouble target_width;
+          gint format_components;
+          gint rc;
+          guint icc_profile_len;
+          guint target_height_rounded;
+          guint target_width_rounded;
+
+          png_save_markers (&self->cinfo, PNG_APP0 + 1, 0xffff);
+          png_save_markers (&self->cinfo, PNG_APP0 + 2, 0xffff);
+          png_save_markers (&self->cinfo, PNG_COM, 0xffff);
+          rc = png_read_header (&self->cinfo, TRUE);
+          self->src_initialized = TRUE;
+
+          if (rc == PNG_SUSPENDED)
+            continue;
+
+          self->got_header = TRUE;
+
+          photos_gegl_buffer_codec_png_parse_exif (self);
+
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Original size: %u×%u",
+                        (guint) self->cinfo.image_width,
+                        (guint) self->cinfo.image_height);
+
+          self->can_set_size = TRUE;
+          g_signal_emit_by_name (self,
+                                 "size-prepared",
+                                 (guint) self->cinfo.image_width,
+                                 (guint) self->cinfo.image_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_literal (error, PHOTOS_ERROR, 0, _("Transformed PNG has invalid width or height"));
+              ret_val = FALSE;
+              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);
+
+          if (target_height_rounded == 0 || target_width_rounded == 0)
+            {
+              g_set_error_literal (error, PHOTOS_ERROR, 0, _("Transformed PNG has zero width or height"));
+              ret_val = FALSE;
+              goto out;
+            }
+
+          self->cinfo.scale_num = 1;
+          for (self->cinfo.scale_denom = 2; self->cinfo.scale_denom <= 8; self->cinfo.scale_denom *= 2)
+            {
+              png_calc_output_dimensions (&self->cinfo);
+              if ((guint) self->cinfo.output_height < target_height_rounded
+                  || (guint) self->cinfo.output_width < target_width_rounded)
+                {
+                  self->cinfo.scale_denom /= 2;
+                  break;
+                }
+            }
+
+          png_calc_output_dimensions (&self->cinfo);
+          photos_debug (PHOTOS_DEBUG_GEGL,
+                        "GeglBufferCodecPng: Mipmap size: %u×%u",
+                        (guint) self->cinfo.output_width,
+                        (guint) self->cinfo.output_height);
+
+          png_read_icc_profile (&self->cinfo, &icc_profile, &icc_profile_len);
+          format = photos_gegl_buffer_codec_png_get_format (self->cinfo.out_color_space,
+                                                             icc_profile,
+                                                             icc_profile_len);
+          if (format == NULL)
+            {
+              const gchar *colorspace_name;
+
+              colorspace_name = photos_gegl_buffer_codec_png_get_colorspace_name 
(self->cinfo.out_color_space);
+              g_set_error (error, PHOTOS_ERROR, 0, _("Unsupported PNG color space (%s)"), colorspace_name);
+              goto out;
+            }
+
+          format_components = babl_format_get_n_components (format);
+          g_assert_cmpint (format_components, ==, self->cinfo.output_components);
+
+          g_assert_null (self->buffer);
+          g_assert_null (self->buffer_mipmap);
+          g_assert_null (self->buffer_zoom_from_mipmap);
+
+          gegl_rectangle_set (&bbox, 0, 0, (guint) self->cinfo.output_width, (guint) 
self->cinfo.output_height);
+          self->buffer_mipmap = gegl_buffer_new (&bbox, format);
+
+          if ((guint) self->cinfo.output_height == target_height_rounded
+              && (guint) self->cinfo.output_width == target_width_rounded)
+            {
+              self->buffer_zoom_from_mipmap = g_object_ref (self->buffer_mipmap);
+              self->buffer = g_object_ref (self->buffer_zoom_from_mipmap);
+            }
+          else
+            {
+              gdouble aspect_ratio = (gdouble) self->cinfo.image_width / (gdouble) self->cinfo.image_height;
+              gdouble target_aspect_ratio = target_width / target_height;
+
+              self->zoom_from_mipmap_x = (gdouble) target_width_rounded / (gdouble) self->cinfo.output_width;
+              self->zoom_from_mipmap_y = (gdouble) target_height_rounded / (gdouble) 
self->cinfo.output_height;
+
+              if (G_APPROX_VALUE (aspect_ratio, target_aspect_ratio, PHOTOS_EPSILON))
+                {
+                  gint x;
+                  gint y;
+                  guint zoom_from_mipmap_height;
+                  guint zoom_from_mipmap_width;
+
+                  self->zoom_from_mipmap_x = MAX (self->zoom_from_mipmap_x, self->zoom_from_mipmap_y);
+                  self->zoom_from_mipmap_y = self->zoom_from_mipmap_x;
+
+                  photos_debug (PHOTOS_DEBUG_GEGL,
+                                "GeglBufferCodecPng: Keep aspect ratio: Zoom from mipmap: %f×%f",
+                                self->zoom_from_mipmap_x,
+                                self->zoom_from_mipmap_y);
+
+                  zoom_from_mipmap_height = (guint) (self->zoom_from_mipmap_y * (gdouble) 
self->cinfo.output_height
+                                                     + 0.5);
+                  zoom_from_mipmap_width = (guint) (self->zoom_from_mipmap_x * (gdouble) 
self->cinfo.output_width
+                                                    + 0.5);
+
+                  photos_debug (PHOTOS_DEBUG_GEGL,
+                                "GeglBufferCodecPng: Keep aspect ratio: Zoom from mipmap size: %u×%u",
+                                zoom_from_mipmap_width,
+                                zoom_from_mipmap_height);
+
+                  g_assert_cmpuint (zoom_from_mipmap_height, >=, target_height_rounded);
+                  g_assert_cmpuint (zoom_from_mipmap_width, >=, target_width_rounded);
+
+                  gegl_rectangle_set (&bbox, 0, 0, zoom_from_mipmap_width, zoom_from_mipmap_height);
+                  self->buffer_zoom_from_mipmap = gegl_buffer_new (&bbox, format);
+
+                  x = (zoom_from_mipmap_width - target_width_rounded) / 2;
+                  y = (zoom_from_mipmap_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_mipmap, &bbox);
+                }
+              else
+                {
+                  GeglMatrix3 affine;
+                  GeglMatrix3 inverse_affine;
+
+                  gegl_rectangle_set (&bbox, 0, 0, target_width_rounded, target_height_rounded);
+                  self->buffer_zoom_from_mipmap = gegl_buffer_new (&bbox, format);
+                  self->buffer = g_object_ref (self->buffer_zoom_from_mipmap);
+
+                  photos_debug (PHOTOS_DEBUG_GEGL,
+                                "GeglBufferCodecPng: Don't keep aspect ratio: Zoom from mipmap: %f×%f",
+                                self->zoom_from_mipmap_x,
+                                self->zoom_from_mipmap_y);
+
+                  gegl_matrix3_identity (&affine);
+                  affine.coeff[0][0] = self->zoom_from_mipmap_x;
+                  affine.coeff[1][1] = self->zoom_from_mipmap_y;
+
+                  gegl_matrix3_copy_into (&inverse_affine, &affine);
+                  gegl_matrix3_invert (&inverse_affine);
+
+                  self->inverse_jacobian.coeff[0][0] = inverse_affine.coeff[0][0];
+                  self->inverse_jacobian.coeff[0][1] = inverse_affine.coeff[0][1];
+                  self->inverse_jacobian.coeff[1][0] = inverse_affine.coeff[1][0];
+                  self->inverse_jacobian.coeff[1][1] = inverse_affine.coeff[1][1];
+
+                  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_mipmap, format, GEGL_SAMPLER_LINEAR);
+                }
+
+              g_object_get (self->buffer_zoom_from_mipmap,
+                            "tile-height", &self->tile_height,
+                            "tile-width", &self->tile_width,
+                            NULL);
+
+              self->tile_stride = self->cinfo.output_components * self->tile_width;
+              self->tile_memory = g_malloc0_n (self->tile_height, self->tile_stride);
+
+              self->mipmap_height_needed_for_zoom = (gint) ((gdouble) self->tile_height
+                                                            * (gdouble) self->cinfo.output_height
+                                                            / (gdouble) target_height_rounded
+                                                            + 0.5);
+            }
+
+          g_object_notify (G_OBJECT (self), "buffer");
+
+          g_assert_null (self->lines);
+
+          if (self->cinfo.output_components > 0
+              && self->cinfo.output_width > 0
+              && self->cinfo.output_width > G_MAXUINT / (guint) self->cinfo.output_components)
+            {
+              g_set_error (error,
+                           PHOTOS_ERROR,
+                           0,
+                           _("Overflow calculating row stride (%u×%u)"),
+                           self->cinfo.output_components,
+                           self->cinfo.output_width);
+              goto out;
+            }
+
+          self->stride_mipmap = (JDIMENSION) self->cinfo.output_components * self->cinfo.output_width;
+          if (self->stride_mipmap % 2 == 1)
+            self->stride_mipmap++;
+
+          self->lines = self->cinfo.mem->alloc_sarray ((j_common_ptr) &self->cinfo,
+                                                       JPOOL_IMAGE,
+                                                       self->stride_mipmap,
+                                                       (JDIMENSION) self->cinfo.rec_outbuf_height);
+
+          self->scanline = 0;
+        }
+      else if (!self->did_prescan)
+        {
+          gint rc;
+
+          self->cinfo.buffered_image = self->cinfo.progressive_mode;
+          rc = png_start_decompress (&self->cinfo);
+          self->cinfo.do_fancy_upsampling = FALSE;
+          self->cinfo.do_block_smoothing = FALSE;
+
+          if (rc == PNG_SUSPENDED)
+            continue;
+
+          self->did_prescan = TRUE;
+        }
+      else if (!self->cinfo.buffered_image)
+        {
+          if (!photos_gegl_buffer_codec_png_load_lines (self, error))
+            goto out;
+
+          if (self->cinfo.output_scanline >= self->cinfo.output_height)
+            {
+              ret_val = TRUE;
+              goto out;
+            }
+        }
+      else
+        {
+          while (!png_input_complete (&self->cinfo))
+            {
+              if (!self->in_output)
+                {
+                  if (png_start_output (&self->cinfo, self->cinfo.input_scan_number))
+                    {
+                      self->in_output = TRUE;
+                      self->scanline = 0;
+                    }
+                  else
+                    {
+                      break;
+                    }
+                }
+
+              if (!photos_gegl_buffer_codec_png_load_lines (self, error))
+                goto out;
+
+              if (self->cinfo.output_scanline >= self->cinfo.output_height && png_finish_output 
(&self->cinfo))
+                self->in_output = FALSE;
+              else
+                break;
+            }
+
+          if (png_input_complete (&self->cinfo))
+            {
+              ret_val = TRUE;
+              goto out;
+            }
+          else
+            {
+              continue;
+            }
+        }
+    }
+
+ out:
+  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);
+
+  self->jerr.error = error;
+
+  if (!sigsetjmp (self->jerr.setjmp_buffer, 1))
+    {
+      if (self->buffer != NULL && self->cinfo.output_scanline < self->cinfo.output_height)
+        {
+          if (self->src.skip_next < sizeof (self->src.buffer) - 2)
+            {
+              self->src.buffer[self->src.skip_next] = (JOCTET) 0xFF;
+              self->src.buffer[self->src.skip_next + 1] = (JOCTET) PNG_EOI;
+              self->src.pub.next_input_byte = &self->src.buffer[self->src.skip_next];
+              self->src.pub.bytes_in_buffer = 2;
+
+              photos_gegl_buffer_codec_png_load_lines (self, NULL);
+            }
+        }
+    }
+
+  /* FIXME: This thing needs to report errors if we have unused image
+   * data.
+   */
+
+  self->jerr.error = error;
+
+  if (sigsetjmp (self->jerr.setjmp_buffer, 1))
+    {
+      ret_val = FALSE;
+    }
+  else
+    {
+      png_finish_decompress (&self->cinfo);
+      ret_val = TRUE;
+    }
+
+  png_destroy_decompress (&self->cinfo);
+  self->decoding = FALSE;
+
+  g_return_val_if_fail (!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_mipmap);
+  g_clear_object (&self->buffer_zoom_from_mipmap);
+  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);
+
+  if (self->decoding)
+    png_destroy_decompress (&self->cinfo);
+
+  g_free (self->tile_memory);
+
+  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 */