[gdk-pixbuf] gdk-pixbuf: Add gdk_pixbuf_calculate_rowstride()

[Bastien Nocera <hadess src gnome org>]

commit c1a969045c056f0180b108a0abeff8b0febce960
Author: Bastien Nocera <hadess hadess net>
Date:   Wed Jul 26 17:01:57 2017 +0200

    gdk-pixbuf: Add gdk_pixbuf_calculate_rowstride()
    
    To calculate the rowstride without allocating memory!
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765094

 configure.ac                 |    2 +-
 gdk-pixbuf/gdk-pixbuf-core.h |    7 +++++
 gdk-pixbuf/gdk-pixbuf.c      |   59 ++++++++++++++++++++++++++++++++---------
 3 files changed, 54 insertions(+), 14 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index f28755c..da86b42 100644
--- a/configure.ac
+++ b/configure.ac
@@ -16,7 +16,7 @@ AC_PREREQ([2.63])
 m4_define([gdk_pixbuf_major_version], [2])
 m4_define([gdk_pixbuf_minor_version], [36])
 m4_define([gdk_pixbuf_micro_version], [7])
-m4_define([gdk_pixbuf_interface_age], [7])
+m4_define([gdk_pixbuf_interface_age], [0])
 m4_define([gdk_pixbuf_binary_age],
           [m4_eval(100 * gdk_pixbuf_minor_version + gdk_pixbuf_micro_version)])
 m4_define([gdk_pixbuf_version],
diff --git a/gdk-pixbuf/gdk-pixbuf-core.h b/gdk-pixbuf/gdk-pixbuf-core.h
index a99cf4e..f4c928d 100644
--- a/gdk-pixbuf/gdk-pixbuf-core.h
+++ b/gdk-pixbuf/gdk-pixbuf-core.h
@@ -270,6 +270,13 @@ GDK_PIXBUF_AVAILABLE_IN_ALL
 GdkPixbuf *gdk_pixbuf_new (GdkColorspace colorspace, gboolean has_alpha, int bits_per_sample,
                           int width, int height);
 
+GDK_PIXBUF_AVAILABLE_IN_2_36
+gint gdk_pixbuf_calculate_rowstride (GdkColorspace colorspace,
+                                    gboolean      has_alpha,
+                                    int           bits_per_sample,
+                                    int           width,
+                                    int           height);
+
 /* Copy a pixbuf */
 GDK_PIXBUF_AVAILABLE_IN_ALL
 GdkPixbuf *gdk_pixbuf_copy (const GdkPixbuf *pixbuf);
diff --git a/gdk-pixbuf/gdk-pixbuf.c b/gdk-pixbuf/gdk-pixbuf.c
index 2ee0b2a..8fe4b0c 100644
--- a/gdk-pixbuf/gdk-pixbuf.c
+++ b/gdk-pixbuf/gdk-pixbuf.c
@@ -422,6 +422,46 @@ free_buffer (guchar *pixels, gpointer data)
 }
 
 /**
+ * gdk_pixbuf_calculate_rowstride:
+ * @colorspace: Color space for image
+ * @has_alpha: Whether the image should have transparency information
+ * @bits_per_sample: Number of bits per color sample
+ * @width: Width of image in pixels, must be > 0
+ * @height: Height of image in pixels, must be > 0
+ *
+ * Calculates the rowstride that an image created with those values would
+ * have. This is useful for front-ends and backends that want to sanity
+ * check image values without needing to create them.
+ *
+ * Return value: the rowstride for the given values, or -1 in case of error.
+ *
+ * Since: 2.36.8
+ */
+gint
+gdk_pixbuf_calculate_rowstride (GdkColorspace colorspace,
+                               gboolean      has_alpha,
+                               int           bits_per_sample,
+                               int           width,
+                               int           height)
+{
+       unsigned int channels;
+
+       g_return_val_if_fail (colorspace == GDK_COLORSPACE_RGB, -1);
+       g_return_val_if_fail (bits_per_sample == 8, -1);
+       g_return_val_if_fail (width > 0, -1);
+       g_return_val_if_fail (height > 0, -1);
+
+       channels = has_alpha ? 4 : 3;
+
+       /* Overflow? */
+       if (width > (G_MAXINT - 3) / channels)
+               return -1;
+
+       /* Always align rows to 32-bit boundaries */
+       return (width * channels + 3) & ~3;
+}
+
+/**
  * gdk_pixbuf_new:
  * @colorspace: Color space for image
  * @has_alpha: Whether the image should have transparency information
@@ -444,23 +484,16 @@ gdk_pixbuf_new (GdkColorspace colorspace,
                 int           height)
 {
        guchar *buf;
-       unsigned int channels;
        int rowstride;
 
-       g_return_val_if_fail (colorspace == GDK_COLORSPACE_RGB, NULL);
-       g_return_val_if_fail (bits_per_sample == 8, NULL);
-       g_return_val_if_fail (width > 0, NULL);
-       g_return_val_if_fail (height > 0, NULL);
-
-       channels = has_alpha ? 4 : 3;
-
-       /* Overflow? */
-       if (width > (G_MAXINT - 3) / channels)
+       rowstride = gdk_pixbuf_calculate_rowstride (colorspace,
+                                                   has_alpha,
+                                                   bits_per_sample,
+                                                   width,
+                                                   height);
+       if (rowstride <= 0)
                return NULL;
 
-       /* Always align rows to 32-bit boundaries */
-       rowstride = (width * channels + 3) & ~3;
-
        buf = g_try_malloc_n (height, rowstride);
        if (!buf)
                return NULL;