[gdk-pixbuf] Move density unit convesion macros into a common header. Fix conversion from dpcm to dpi

[Robert Ancell <rancell src gnome org>]

commit c009067769567e235bd75da5514451467b805384
Author: Robert Ancell <robert ancell canonical com>
Date:   Wed Oct 22 11:38:10 2014 -0400

    Move density unit convesion macros into a common header. Fix conversion from dpcm to dpi

 gdk-pixbuf/gdk-pixbuf-private.h |    6 ++++++
 gdk-pixbuf/io-jpeg.c            |    2 --
 gdk-pixbuf/io-png.c             |    3 ---
 3 files changed, 6 insertions(+), 5 deletions(-)
---
diff --git a/gdk-pixbuf/gdk-pixbuf-private.h b/gdk-pixbuf/gdk-pixbuf-private.h
index e209694..e985459 100644
--- a/gdk-pixbuf/gdk-pixbuf-private.h
+++ b/gdk-pixbuf/gdk-pixbuf-private.h
@@ -45,6 +45,12 @@ typedef struct _GdkPixbufClass GdkPixbufClass;
 #define GDK_IS_PIXBUF_CLASS(klass)   (G_TYPE_CHECK_CLASS_TYPE ((klass), GDK_TYPE_PIXBUF))
 #define GDK_PIXBUF_GET_CLASS(obj)    (G_TYPE_INSTANCE_GET_CLASS ((obj), GDK_TYPE_PIXBUF, GdkPixbufClass))
 
+/* Helper macros to convert between density units */
+#define DPI_TO_DPM(value) ((int) round ((value) * 1000 / 25.4))
+#define DPI_TO_DPCM(value) ((int) round ((value) / 2.54))
+#define DPM_TO_DPI(value) ((int) round ((value) * 25.4 / 1000))
+#define DPCM_TO_DPI(value) ((int) round ((value) * 2.54))
+
 /* Private part of the GdkPixbuf structure */
 struct _GdkPixbuf {
         GObject parent_instance;
diff --git a/gdk-pixbuf/io-jpeg.c b/gdk-pixbuf/io-jpeg.c
index 5e266b6..c43aee6 100644
--- a/gdk-pixbuf/io-jpeg.c
+++ b/gdk-pixbuf/io-jpeg.c
@@ -46,8 +46,6 @@
 /* we are a "source manager" as far as libjpeg is concerned */
 #define JPEG_PROG_BUF_SIZE 65536
 
-#define DPCM_TO_DPI(value) ((int) round ((value) / 2.54))
-
 typedef struct {
        struct jpeg_source_mgr pub;   /* public fields */
 
diff --git a/gdk-pixbuf/io-png.c b/gdk-pixbuf/io-png.c
index 35708e9..c1e6bcd 100644
--- a/gdk-pixbuf/io-png.c
+++ b/gdk-pixbuf/io-png.c
@@ -31,9 +31,6 @@
 
 
 
-#define DPI_TO_DPM(value) ((int) round ((value) * 1000 / 25.4))
-#define DPM_TO_DPI(value) ((int) round ((value) * 25.4 / 1000))
-
 static gboolean
 setup_png_transformations(png_structp png_read_ptr, png_infop png_info_ptr,
                           GError **error,