+
+void
+ev_document_misc_invert_surface (cairo_surface_t *surface) {
+#if CAIRO_VERSION > CAIRO_VERSION_ENCODE(1, 9, 2)
+ cairo_t *cr;
+
+ cr = cairo_create (surface);
+
+ /* white + DIFFERENCE -> invert */
+ cairo_set_operator (cr, CAIRO_OPERATOR_DIFFERENCE);
+ cairo_set_source_rgb (cr, 1., 1., 1.);
+ cairo_paint(cr);
+ cairo_destroy (cr);
+#else
+ guchar *data;
+ gint rowstride;
+ gint width, height;
+ gint x, y;
+
+ data = cairo_image_surface_get_data (surface);
+ rowstride = cairo_image_surface_get_stride (surface);
+ width = cairo_image_surface_get_width (surface);
+ height = cairo_image_surface_get_height (surface);
+
+ for (y = 0; y < height; y++) {
+ guchar *p = data + y * rowstride;
+
+ for (x = 0; x < width; x++) {
+ p[0] = 255 - p[0];
+ p[1] = 255 - p[1];
+ p[2] = 255 - p[2];
+ p += 4;
+ }
+ }
+
+ cairo_surface_mark_dirty (surface);
+#endif
+}
+
+void
+ev_document_misc_invert_pixbuf (GdkPixbuf *pixbuf)
+{
+ guchar *data, *p;
+ guint width, height, x, y, rowstride, n_channels;
+
+ n_channels = gdk_pixbuf_get_n_channels (pixbuf);
+ g_assert (gdk_pixbuf_get_colorspace (pixbuf) == GDK_COLORSPACE_RGB);
+ g_assert (gdk_pixbuf_get_bits_per_sample (pixbuf) == 8);
+
+ /* First grab a pointer to the raw pixel data. */
+ data = gdk_pixbuf_get_pixels (pixbuf);
+
+ /* Find the number of bytes per row (could be padded). */
+ rowstride = gdk_pixbuf_get_rowstride (pixbuf);
+
+ width = gdk_pixbuf_get_width (pixbuf);
+ height = gdk_pixbuf_get_height (pixbuf);
+ for (x = 0; x < width; x++) {
+ for (y = 0; y < height; y++) {
+ /* Calculate pixel's offset into the data array. */
+ p = data + x * n_channels + y * rowstride;
+ /* Change the RGB values*/
+ p[0] = 255 - p[0];
+ p[1] = 255 - p[1];
+ p[2] = 255 - p[2];
+ }
+ }
+}
+
+gdouble
+ev_document_misc_get_screen_dpi (GdkScreen *screen)
+{
+ gdouble dp, di;
+
+ /*diagonal in pixels*/
+ dp = hypot (gdk_screen_get_width (screen), gdk_screen_get_height (screen));
+
+ /*diagonal in inches*/
+ di = hypot (gdk_screen_get_width_mm(screen), gdk_screen_get_height_mm (screen)) / 25.4;
+
+ return (dp / di);
+}