[gtk/gamma-shenanigans: 2/3] Add gdk_texture_new_from_png

[Matthias Clasen <matthiasc src gnome org>]

commit 5eb11870da803746a301b0942fca896174deb256
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Sep 5 20:11:40 2021 -0400

    Add gdk_texture_new_from_png
    
    This is using libpng to load a png into a memory
    texture, applying gamma from the file.
    
    As a consequence, we are now linking against libpng.

 gdk/gdktexture.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 gdk/gdktexture.h |  4 ++++
 gdk/meson.build  |  4 ++--
 meson.build      |  1 +
 4 files changed, 78 insertions(+), 2 deletions(-)
---
diff --git a/gdk/gdktexture.c b/gdk/gdktexture.c
index 7ac4f1bb53..ece69ffe95 100644
--- a/gdk/gdktexture.c
+++ b/gdk/gdktexture.c
@@ -46,6 +46,7 @@
 #include "gdksnapshot.h"
 
 #include <graphene.h>
+#include <png.h>
 
 /* HACK: So we don't need to include any (not-yet-created) GSK or GTK headers */
 void
@@ -575,3 +576,73 @@ gdk_texture_save_to_png (GdkTexture *texture,
 
   return result;
 }
+
+/**
+ * gdk_texture_new_from_png:
+ * @file: `GFile` to load
+ * @error: Return location for an error
+ *
+ * Creates a new texture by loading an png image from a file.
+ *
+ * In contrast to [ctor@Gdk.Texture.new_from_file], this
+ * function tries to preserve all the data that the PNG
+ * format provides, and e.g. applies Gamma correction if
+ * that information is available in the file.
+ *
+ * If %NULL is returned, then @error will be set.
+ *
+ * Return value: A newly-created `GdkTexture`
+ *
+ * Since: 4.6
+ */
+GdkTexture *
+gdk_texture_new_from_png (GFile   *file,
+                          GError **error)
+{
+  png_image image = { NULL, PNG_IMAGE_VERSION, 0, };
+  GBytes *contents;
+  gconstpointer data;
+  gsize size;
+  gsize stride;
+  guint16 *buffer;
+  GBytes *bytes;
+  GdkTexture *texture;
+
+  contents = g_file_load_bytes (file, NULL, NULL, error);
+  if (!contents)
+    return NULL;
+
+  data = g_bytes_get_data (contents, &size);
+  png_image_begin_read_from_memory (&image, data, size);
+
+  image.format = PNG_FORMAT_LINEAR_RGB_ALPHA;
+
+  stride = PNG_IMAGE_ROW_STRIDE (image);
+  size = PNG_IMAGE_BUFFER_SIZE (image, stride);
+  buffer = malloc (size);
+
+  png_image_finish_read (&image, NULL, buffer, stride, NULL);
+
+  g_bytes_unref (contents);
+
+  if (PNG_IMAGE_FAILED (image))
+    {
+      g_free (buffer);
+      g_set_error (error,
+                   G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "%s", image.message);
+      return NULL;
+    }
+
+  bytes = g_bytes_new_take (buffer, size);
+
+  texture = gdk_memory_texture_new (image.width, image.height,
+                                    GDK_MEMORY_R16G16B16A16_PREMULTIPLIED,
+                                    bytes, 2 * stride);
+
+  g_bytes_unref (bytes);
+
+  png_image_free (&image);
+
+  return texture;
+}
diff --git a/gdk/gdktexture.h b/gdk/gdktexture.h
index f3d0bc9765..2c822e1118 100644
--- a/gdk/gdktexture.h
+++ b/gdk/gdktexture.h
@@ -50,6 +50,10 @@ GDK_AVAILABLE_IN_ALL
 GdkTexture *            gdk_texture_new_from_file              (GFile           *file,
                                                                 GError         **error);
 
+GDK_AVAILABLE_IN_4_6
+GdkTexture *            gdk_texture_new_from_png               (GFile           *file,
+                                                                GError         **error);
+
 GDK_AVAILABLE_IN_ALL
 int                     gdk_texture_get_width                  (GdkTexture      *texture) G_GNUC_PURE;
 GDK_AVAILABLE_IN_ALL
diff --git a/gdk/meson.build b/gdk/meson.build
index db64565c2c..6539c225f4 100644
--- a/gdk/meson.build
+++ b/gdk/meson.build
@@ -254,8 +254,8 @@ endif
 
 libgdk = static_library('gdk',
   sources: [gdk_sources, gdk_backends_gen_headers, gdkconfig],
-  dependencies: gdk_deps + [libgtk_css_dep],
-  link_with: [libgtk_css, ],
+  dependencies: gdk_deps + [libgtk_css_dep, png_dep],
+  link_with: [libgtk_css],
   include_directories: [confinc, gdkx11_inc, wlinc],
   c_args: libgdk_c_args + common_cflags,
   link_whole: gdk_backends,
diff --git a/meson.build b/meson.build
index c0b5407a0d..fc50b6e3eb 100644
--- a/meson.build
+++ b/meson.build
@@ -394,6 +394,7 @@ pangocairo_dep = dependency('pangocairo', version: pango_req,
 pixbuf_dep     = dependency('gdk-pixbuf-2.0', version: gdk_pixbuf_req,
                             fallback : ['gdk-pixbuf', 'gdkpixbuf_dep'],
                             default_options: ['png=enabled', 'jpeg=enabled', 'builtin_loaders=png,jpeg', 
'man=false'])
+png_dep        = dependency('libpng16')
 epoxy_dep      = dependency('epoxy', version: epoxy_req,
                             fallback: ['libepoxy', 'libepoxy_dep'])
 harfbuzz_dep   = dependency('harfbuzz', version: '>= 2.1.0', required: false,