[png] Complete the idempotent read_png() -> write_png()

Write out the original PNG mime-data if attached to the surface during
cairo_surface_write_to_png(). Similar to how the compressed alternate
representations are handled by the other backends.

Note: by automatically attaching and using the mime-data in preference to
the image data, we break the read_from_png(); draw(); write_to_png()
cycle.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/cairo-png.c b/src/cairo-png.c
index b4aeb0813..a130ba25d 100644
--- a/src/cairo-png.c
+++ b/src/cairo-png.c
@@ -148,6 +148,8 @@ write_png (cairo_surface_t	*surface,
     png_info *info;
     png_byte **volatile rows = NULL;
     png_color_16 white;
+    const unsigned char *mime_data;
+    unsigned int mime_data_length;
     int png_color_type;
     int depth;
 
@@ -196,6 +198,18 @@ write_png (cairo_surface_t	*surface,
 
     png_set_write_fn (png, closure, write_func, png_simple_output_flush_fn);
 
+    /* XXX This is very questionable.
+     * This breaks the read_from_png(); draw(); write_to_png(); cycle, but
+     * that is affected by mime-data in general. OTOH, by using mime-data
+     * here we are consistent with the other backends.
+     */
+    cairo_surface_get_mime_data (surface, CAIRO_MIME_TYPE_PNG,
+				 &mime_data, &mime_data_length);
+    if (mime_data != NULL) {
+	write_func (png, (png_bytep) mime_data, mime_data_length);
+	goto BAIL3;
+    }
+
     switch (image->format) {
     case CAIRO_FORMAT_ARGB32:
 	depth = 8;