Re: Inline SVG images and the need to prefix identifiers

From 3b20b17533883d7f8e9181ae336e6103948d7293 Mon Sep 17 00:00:00 2001
From: Christian von Schultz <[email protected]>
Date: Fri, 23 Oct 2015 15:05:29 +0200
Subject: [PATCH] cairo-svg: Added cairo_svg_surface_set_id_attribute_prefix()
 and related code.

Inserts document->idprefix in every id attribute of the generated SVG file.
This is useful if several SVG files will be merged in a single
XML document (e.g. XHTML with inline SVG): You can prevent otherwise
inevitable id clashes by giving the different SVG files different
idprefix values.
---
 src/cairo-svg-surface.c | 134 ++++++++++++++++++++++++++++++++++++------------
 src/cairo-svg.h         |   4 ++
 2 files changed, 106 insertions(+), 32 deletions(-)

diff --git a/src/cairo-svg-surface.c b/src/cairo-svg-surface.c
index 2e023b3..06a5248 100644
--- a/src/cairo-svg-surface.c
+++ b/src/cairo-svg-surface.c
@@ -139,6 +139,8 @@ struct cairo_svg_document {
     cairo_output_stream_t *xml_node_defs;
     cairo_output_stream_t *xml_node_glyphs;
 
+    char *idprefix;
+
     unsigned int linear_pattern_id;
     unsigned int radial_pattern_id;
     unsigned int pattern_id;
@@ -330,6 +332,36 @@ _extract_svg_surface (cairo_surface_t		 *surface,
 }
 
 /**
+ * cairo_svg_surface_set_id_attribute_prefix:
+ * @surface: a SVG #cairo_surface_t
+ * @prefix:  a char*
+ *
+ * Inserts @prefix in every id attribute of the generated SVG file.
+ * This is useful if several SVG files will be merged in a single
+ * XML document (e.g. XHTML with inline SVG): You can prevent otherwise
+ * inevitable id clashes by giving the different SVG files different
+ * @prefix values.
+ **/
+cairo_status_t
+cairo_svg_surface_set_id_attribute_prefix (cairo_surface_t	*abstract_surface,
+					   const char		*prefix)
+{
+    cairo_svg_surface_t *surface = NULL; /* hide compiler warning */
+    size_t size;
+
+    if (! _extract_svg_surface (abstract_surface, &surface))
+	return CAIRO_STATUS_SURFACE_TYPE_MISMATCH;
+
+    size = strlen(prefix) + 1;
+    surface->document->idprefix = realloc (surface->document->idprefix, size);
+    if (unlikely (surface->document->idprefix == NULL))
+	return _cairo_error (CAIRO_STATUS_NO_MEMORY);
+    strncpy(surface->document->idprefix, prefix, size);
+
+    return CAIRO_STATUS_SUCCESS;
+}
+
+/**
  * cairo_svg_surface_restrict_to_version:
  * @surface: a SVG #cairo_surface_t
  * @version: SVG version
@@ -444,8 +476,9 @@ _cairo_svg_surface_clipper_intersect_clip_path (cairo_surface_clipper_t *clipper
 	return CAIRO_STATUS_SUCCESS;
 
     _cairo_output_stream_printf (document->xml_node_defs,
-				 "<clipPath id=\"clip%d\">\n"
+				 "<clipPath id=\"%sclip%d\">\n"
 				 "  <path ",
+				 document->idprefix,
 				 document->clip_id);
     _cairo_svg_surface_emit_path (document->xml_node_defs, path, NULL);
 
@@ -454,8 +487,9 @@ _cairo_svg_surface_clipper_intersect_clip_path (cairo_surface_clipper_t *clipper
 				 "</clipPath>\n");
 
     _cairo_output_stream_printf (surface->xml_node,
-				 "<g clip-path=\"url(#clip%d)\" "
+				 "<g clip-path=\"url(#%sclip%d)\" "
 				 "clip-rule=\"%s\">\n",
+				 document->idprefix,
 				 document->clip_id,
 				 fill_rule == CAIRO_FILL_RULE_EVEN_ODD ?
 				 "evenodd" : "nonzero");
@@ -840,7 +874,8 @@ _cairo_svg_document_emit_glyph (cairo_svg_document_t	*document,
     cairo_int_status_t	     status;
 
     _cairo_output_stream_printf (document->xml_node_glyphs,
-				 "<symbol overflow=\"visible\" id=\"glyph%d-%d\">\n",
+				 "<symbol overflow=\"visible\" id=\"%sglyph%d-%d\">\n",
+				 document->idprefix,
 				 font_id,
 				 subset_glyph_index);
 
@@ -1026,14 +1061,15 @@ _cairo_svg_surface_emit_alpha_filter (cairo_svg_document_t *document)
 	return;
 
     _cairo_output_stream_printf (document->xml_node_defs,
-				 "<filter id=\"alpha\" "
+				 "<filter id=\"%salpha\" "
 				 "filterUnits=\"objectBoundingBox\" "
 				 "x=\"0%%\" y=\"0%%\" "
 				 "width=\"100%%\" height=\"100%%\">\n"
 				 "  <feColorMatrix type=\"matrix\" "
 				 "in=\"SourceGraphic\" "
 				 "values=\"0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0\"/>\n"
-				 "</filter>\n");
+				 "</filter>\n",
+				 document->idprefix);
 
     document->alpha_filter = TRUE;
 }
@@ -1300,7 +1336,8 @@ _cairo_svg_surface_emit_surface (cairo_svg_document_t *document,
     assert (is_bounded);
 
     _cairo_output_stream_printf (document->xml_node_defs,
-				 "<image id=\"image%d\" width=\"%d\" height=\"%d\"",
+				 "<image id=\"%simage%d\" width=\"%d\" height=\"%d\"",
+				 document->idprefix,
 				 surface->unique_id,
 				 extents.width, extents.height);
 
@@ -1356,9 +1393,10 @@ _cairo_svg_surface_emit_composite_surface_pattern (cairo_output_stream_t   *outp
 	assert (is_bounded);
 
 	_cairo_output_stream_printf (output,
-				     "<pattern id=\"pattern%d\" "
+				     "<pattern id=\"%spattern%d\" "
 				     "patternUnits=\"userSpaceOnUse\" "
 				     "width=\"%d\" height=\"%d\" ",
+				     svg_surface->document->idprefix,
 				     pattern_id,
 				     extents.width, extents.height);
 	_cairo_svg_surface_emit_transform (output,
@@ -1368,7 +1406,8 @@ _cairo_svg_surface_emit_composite_surface_pattern (cairo_output_stream_t   *outp
     }
 
     _cairo_output_stream_printf (output,
-				 "<use xlink:href=\"#image%d\"",
+				 "<use xlink:href=\"#%simage%d\"",
+				 svg_surface->document->idprefix,
 				 pattern->surface->unique_id);
     if (extra_attributes)
 	_cairo_output_stream_printf (output, " %s", extra_attributes);
@@ -1437,9 +1476,10 @@ _cairo_svg_surface_emit_recording_surface (cairo_svg_document_t      *document,
     if (! svg_surface->is_base_clip_emitted) {
 	svg_surface->is_base_clip_emitted = TRUE;
 	_cairo_output_stream_printf (document->xml_node_defs,
-				     "<clipPath id=\"clip%d\">\n"
+				     "<clipPath id=\"%sclip%d\">\n"
 				     "  <rect width=\"%f\" height=\"%f\"/>\n"
 				     "</clipPath>\n",
+				     document->idprefix,
 				     svg_surface->base_clip,
 				     svg_surface->width,
 				     svg_surface->height);
@@ -1448,16 +1488,21 @@ _cairo_svg_surface_emit_recording_surface (cairo_svg_document_t      *document,
     if (source->base.content == CAIRO_CONTENT_ALPHA) {
 	_cairo_svg_surface_emit_alpha_filter (document);
 	_cairo_output_stream_printf (document->xml_node_defs,
-				     "<g id=\"surface%d\" "
-				     "clip-path=\"url(#clip%d)\" "
-				     "filter=\"url(#alpha)\">\n",
+				     "<g id=\"%ssurface%d\" "
+				     "clip-path=\"url(#%sclip%d)\" "
+				     "filter=\"url(#%salpha)\">\n",
+				     document->idprefix,
 				     source->base.unique_id,
-				     svg_surface->base_clip);
+				     document->idprefix,
+				     svg_surface->base_clip,
+				     document->idprefix);
     } else {
 	_cairo_output_stream_printf (document->xml_node_defs,
-				     "<g id=\"surface%d\" "
-				     "clip-path=\"url(#clip%d)\">\n",
+				     "<g id=\"%ssurface%d\" "
+				     "clip-path=\"url(#%sclip%d)\">\n",
+				     document->idprefix,
 				     source->base.unique_id,
+				     document->idprefix,
 				     svg_surface->base_clip);
     }
 
@@ -1529,9 +1574,10 @@ _cairo_svg_surface_emit_composite_recording_pattern (cairo_output_stream_t	*outp
 
     if (pattern_id != invalid_pattern_id) {
 	_cairo_output_stream_printf (output,
-				     "<pattern id=\"pattern%d\" "
+				     "<pattern id=\"%spattern%d\" "
 				     "patternUnits=\"userSpaceOnUse\" "
 				     "width=\"%d\" height=\"%d\"",
+				     document->idprefix,
 				     pattern_id,
 				     recording_surface->extents.width,
 				     recording_surface->extents.height);
@@ -1540,7 +1586,8 @@ _cairo_svg_surface_emit_composite_recording_pattern (cairo_output_stream_t	*outp
     }
 
     _cairo_output_stream_printf (output,
-				 "<use xlink:href=\"#surface%d\"",
+				 "<use xlink:href=\"#%ssurface%d\"",
+				 document->idprefix,
 				 recording_surface->base.unique_id);
 
     if (pattern_id == invalid_pattern_id) {
@@ -1620,8 +1667,9 @@ _cairo_svg_surface_emit_surface_pattern (cairo_svg_surface_t	 *surface,
 	return status;
 
     _cairo_output_stream_printf (style,
-				 "%s:url(#pattern%d);",
+				 "%s:url(#%spattern%d);",
 				 is_stroke ? "stroke" : "fill",
+				 document->idprefix,
 				 pattern_id);
 
     return CAIRO_STATUS_SUCCESS;
@@ -1824,9 +1872,10 @@ _cairo_svg_surface_emit_linear_pattern (cairo_svg_surface_t    *surface,
     assert (status == CAIRO_STATUS_SUCCESS);
 
     _cairo_output_stream_printf (document->xml_node_defs,
-				 "<linearGradient id=\"linear%d\" "
+				 "<linearGradient id=\"%slinear%d\" "
 				 "gradientUnits=\"userSpaceOnUse\" "
 				 "x1=\"%f\" y1=\"%f\" x2=\"%f\" y2=\"%f\" ",
+				 document->idprefix,
 				 document->linear_pattern_id,
 				 pattern->pd1.x, pattern->pd1.y,
 				 pattern->pd2.x, pattern->pd2.y);
@@ -1845,8 +1894,9 @@ _cairo_svg_surface_emit_linear_pattern (cairo_svg_surface_t    *surface,
 				 "</linearGradient>\n");
 
     _cairo_output_stream_printf (style,
-				 "%s:url(#linear%d);",
+				 "%s:url(#%slinear%d);",
 				 is_stroke ? "stroke" : "fill",
+				 document->idprefix,
 				 document->linear_pattern_id);
 
     document->linear_pattern_id++;
@@ -1898,10 +1948,11 @@ _cairo_svg_surface_emit_radial_pattern (cairo_svg_surface_t    *surface,
 	unsigned int n_stops = pattern->base.n_stops;
 
 	_cairo_output_stream_printf (document->xml_node_defs,
-				     "<radialGradient id=\"radial%d\" "
+				     "<radialGradient id=\"%sradial%d\" "
 				     "gradientUnits=\"userSpaceOnUse\" "
 				     "cx=\"%f\" cy=\"%f\" "
 				     "fx=\"%f\" fy=\"%f\" r=\"%f\" ",
+				     document->idprefix,
 				     document->radial_pattern_id,
 				     x1, y1,
 				     x1, y1, r1);
@@ -1979,10 +2030,11 @@ _cairo_svg_surface_emit_radial_pattern (cairo_svg_surface_t    *surface,
 	}
 
 	_cairo_output_stream_printf (document->xml_node_defs,
-				     "<radialGradient id=\"radial%d\" "
+				     "<radialGradient id=\"%sradial%d\" "
 				     "gradientUnits=\"userSpaceOnUse\" "
 				     "cx=\"%f\" cy=\"%f\" "
 				     "fx=\"%f\" fy=\"%f\" r=\"%f\" ",
+				     document->idprefix,
 				     document->radial_pattern_id,
 				     x1, y1,
 				     fx, fy, r1);
@@ -2027,8 +2079,9 @@ _cairo_svg_surface_emit_radial_pattern (cairo_svg_surface_t    *surface,
 				 "</radialGradient>\n");
 
     _cairo_output_stream_printf (style,
-				 "%s:url(#radial%d);",
+				 "%s:url(#%sradial%d);",
 				 is_stroke ? "stroke" : "fill",
+				 document->idprefix,
 				 document->radial_pattern_id);
 
     document->radial_pattern_id++;
@@ -2427,10 +2480,14 @@ _cairo_svg_surface_mask (void		    *abstract_surface,
     mask_id = _cairo_svg_document_allocate_mask_id (document);
 
     _cairo_output_stream_printf (mask_stream,
-				 "<mask id=\"mask%d\">\n"
-				 "%s",
-				 mask_id,
-				 discard_filter ? "" : "  <g filter=\"url(#alpha)\">\n");
+				 "<mask id=\"%smask%d\">\n",
+				 document->idprefix,
+				 mask_id);
+    if (!discard_filter) {
+	_cairo_output_stream_printf (mask_stream,
+				     "  <g filter=\"url(#%salpha)\">\n",
+				     document->idprefix);
+    }
     status = _cairo_svg_surface_emit_paint (mask_stream, surface, CAIRO_OPERATOR_OVER, mask, source, NULL);
     if (unlikely (status)) {
 	cairo_status_t ignore = _cairo_output_stream_destroy (mask_stream);
@@ -2448,7 +2505,8 @@ _cairo_svg_surface_mask (void		    *abstract_surface,
     if (unlikely (status))
 	return status;
 
-    snprintf (buffer, sizeof buffer, "mask=\"url(#mask%d)\"",
+    snprintf (buffer, sizeof buffer, "mask=\"url(#%smask%d)\"",
+	      document->idprefix,
 	      mask_id);
     status = _cairo_svg_surface_emit_paint (surface->xml_node, surface, op, source, 0, buffer);
     if (unlikely (status))
@@ -2558,8 +2616,9 @@ _cairo_svg_surface_show_glyphs (void			*abstract_surface,
 	    return status;
 
 	_cairo_output_stream_printf (surface->xml_node,
-				     "  <use xlink:href=\"#glyph%d-%d\" "
+				     "  <use xlink:href=\"#%sglyph%d-%d\" "
 				     "x=\"%f\" y=\"%f\"/>\n",
+				     document->idprefix,
 				     subset_glyph.font_id,
                                      subset_glyph.subset_glyph_index,
 				     glyphs[i].x, glyphs[i].y);
@@ -2663,11 +2722,17 @@ _cairo_svg_document_create (cairo_output_stream_t	 *output_stream,
     if (unlikely (document == NULL))
 	return _cairo_error (CAIRO_STATUS_NO_MEMORY);
 
+    document->idprefix = strdup("");
+    if (unlikely (document->idprefix == NULL)) {
+	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
+	goto CLEANUP_DOCUMENT;
+    }
+
     /* The use of defs for font glyphs imposes no per-subset limit. */
     document->font_subsets = _cairo_scaled_font_subsets_create_scaled ();
     if (unlikely (document->font_subsets == NULL)) {
 	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
-	goto CLEANUP_DOCUMENT;
+	goto CLEANUP_IDPREFIX;
     }
 
     document->output_stream = output_stream;
@@ -2706,6 +2771,8 @@ _cairo_svg_document_create (cairo_output_stream_t	 *output_stream,
   CLEANUP_NODE_DEFS:
     status_ignored = _cairo_output_stream_destroy (document->xml_node_defs);
     _cairo_scaled_font_subsets_destroy (document->font_subsets);
+  CLEANUP_IDPREFIX:
+    free (document->idprefix);
   CLEANUP_DOCUMENT:
     free (document);
     return status;
@@ -2736,6 +2803,7 @@ _cairo_svg_document_destroy (cairo_svg_document_t *document)
 
     status = _cairo_svg_document_finish (document);
 
+    free (document->idprefix);
     free (document);
 
     return status;
@@ -2817,7 +2885,8 @@ _cairo_svg_document_finish (cairo_svg_document_t *document)
 		page = _cairo_array_index (&surface->page_set, i);
 		_cairo_output_stream_printf (output, "<page>\n");
 		_cairo_output_stream_printf (output,
-					     "<g id=\"surface%d\">\n",
+					     "<g id=\"%ssurface%d\">\n",
+					     document->idprefix,
 					     page->surface_id);
 		_cairo_memory_stream_copy (page->xml_node, output);
 		_cairo_output_stream_printf (output, "</g>\n</page>\n");
@@ -2826,7 +2895,8 @@ _cairo_svg_document_finish (cairo_svg_document_t *document)
 	} else if (surface->page_set.num_elements > 0) {
 	    page = _cairo_array_index (&surface->page_set, surface->page_set.num_elements - 1);
 	    _cairo_output_stream_printf (output,
-					 "<g id=\"surface%d\">\n",
+					 "<g id=\"%ssurface%d\">\n",
+					 document->idprefix,
 					 page->surface_id);
 	    _cairo_memory_stream_copy (page->xml_node, output);
 	    _cairo_output_stream_printf (output, "</g>\n");
diff --git a/src/cairo-svg.h b/src/cairo-svg.h
index 592c645..71ac4f5 100644
--- a/src/cairo-svg.h
+++ b/src/cairo-svg.h
@@ -64,6 +64,10 @@ cairo_svg_surface_create_for_stream (cairo_write_func_t	write_func,
 				     double		width_in_points,
 				     double		height_in_points);
 
+cairo_public cairo_status_t
+cairo_svg_surface_set_id_attribute_prefix (cairo_surface_t	*abstract_surface,
+					   const char		*prefix);
+
 cairo_public void
 cairo_svg_surface_restrict_to_version (cairo_surface_t 		*surface,
 				       cairo_svg_version_t  	 version);
-- 
2.4.10