Add a rendering parameter to ag_chart_create_svg()

Based upon this parameter a <rect> is included in the resulting SVG
document, providing a background color, and so is the chart CSS.

src/ag-chart.c

@@ -1393,7 +1393,11 @@ ag_chart_sort_planets_by_position(GswePlanetData *planet1,
 }
 
 gchar *
-ag_chart_create_svg(AgChart *chart, gsize *length, GError **err)
+ag_chart_create_svg(
+        AgChart  *chart,
+        gsize    *length,
+        gboolean rendering,
+        GError   **err)
 {
     xmlDocPtr         doc = create_save_doc(chart),
                       xslt_doc,
@@ -1406,7 +1410,8 @@ ag_chart_create_svg(AgChart *chart, gsize *length, GError **err)
                       antiscia_node = NULL,
                       node          = NULL;
     gchar             *value,
-                      *save_content = NULL;
+                      *save_content = NULL,
+                      **params;
     const gchar       *xslt_content;
     GList             *houses,
                       *house,
@@ -1710,15 +1715,22 @@ ag_chart_create_svg(AgChart *chart, gsize *length, GError **err)
         return NULL;
     }
 
+    params = g_new0(gchar *, 3);
+    params[0] = "rendering";
+    params[1] = (rendering) ? "'yes'" : "'no'";
+
     // libxml2 messes up the output, as it prints decimal floating point
     // numbers in a localized format. It is not good in locales that use a
     // character for decimal separator other than a dot. So let's just use the
     // C locale until the SVG is generated.
     current_locale = uselocale(newlocale(LC_ALL, "C", 0));
-    svg_doc        = xsltApplyStylesheet(xslt_proc, doc, NULL);
+
+    svg_doc        = xsltApplyStylesheet(xslt_proc, doc, (const char **)params);
+
     uselocale(current_locale);
     xsltFreeStylesheet(xslt_proc);
     xmlFreeDoc(doc);
+    g_free(params);
 
     // Now, svg_doc contains the generated SVG file
 
@@ -1752,7 +1764,7 @@ ag_chart_export_svg_to_file(AgChart *chart, GFile *file, GError **err)
     gchar *svg;
     gsize length;
 
-    if ((svg = ag_chart_create_svg(chart, &length, err)) == NULL) {
+    if ((svg = ag_chart_create_svg(chart, &length, TRUE, err)) == NULL) {
         return;
     }
 

src/ag-chart.h

@@ -86,6 +86,7 @@ const gchar *ag_chart_get_city(AgChart *chart);
 
 gchar *ag_chart_create_svg(AgChart  *chart,
                            gsize    *length,
+                           gboolean rendering,
                            GError   **err);
 
 GList *ag_chart_get_planets(AgChart *chart);

src/ag-window.c

@@ -496,6 +496,7 @@ ag_window_redraw_chart(AgWindow *window)
     gchar           *svg_content = ag_chart_create_svg(
             priv->chart,
             &length,
+            FALSE,
             &err
         );
 

src/resources/ui/chart-default.css

@@ -134,3 +134,7 @@ line.antiscion {
     stroke: #000000;
     stroke-dasharray: 20,10;
 }
+
+#background {
+    fill: #ffffff;
+}

src/resources/ui/chart-default.xsl

@@ -69,6 +69,15 @@
             version="1.0">
             <xsl:attribute name="width"><xsl:value-of select="$image_size"/></xsl:attribute>
             <xsl:attribute name="height"><xsl:value-of select="$image_size"/></xsl:attribute>
+
+            <xsl:choose>
+              <xsl:when test="$rendering='yes'">
+                <style type="text/css">
+                  <xi:include href="gres://ui/chart-default.css" parse="text"/>
+                </style>
+              </xsl:when>
+            </xsl:choose>
+
             <title>
                 <xsl:value-of select="concat(
                     'Natal chart of ',
@@ -116,6 +125,16 @@
                     <polygon points="0.0,0.0 7.0,-2.0 5.0,0.0 7.0,2.0" />
                 </marker>
             </defs>
+
+            <xsl:choose>
+              <xsl:when test="$rendering='yes'">
+                <rect id="background" x="0" y="0">
+                  <xsl:attribute name="width"><xsl:value-of select="$image_size"/></xsl:attribute>
+                  <xsl:attribute name="height"><xsl:value-of select="$image_size"/></xsl:attribute>
+                </rect>
+              </xsl:when>
+            </xsl:choose>
+
             <g id="chart">
                 <xsl:attribute name="transform"><xsl:value-of select="concat('translate(', $image_size div 2, ',', $image_size div 2, ')')" /></xsl:attribute>
                 <g id="moonless_chart">