Working out more image_url stuff. Have a reasonably simple solution.

context.cpp

@@ -51,7 +51,7 @@ namespace Sass {
     color_names_to_values(map<string, Node>()),
     color_values_to_names(map<Node, string>()),
     new_Node(Node_Factory()),
-    image_path(""),
+    image_path(0),
     ref_count(0),
     has_extensions(false)
   {

context.hpp

@@ -50,7 +50,7 @@ namespace Sass {
     map<string, Node> color_names_to_values;
     map<Node, string> color_values_to_names;
     Node_Factory new_Node;
-    string image_path;
+    char* image_path;
     size_t ref_count;
     // string sass_path;
     // string css_path;

document_parser.cpp

@@ -827,6 +827,7 @@ namespace Sass {
       if (!lex< exactly<')'> >()) throw_syntax_error("call to image-url is missing ')'");
       Node the_call(context.new_Node(Node::image_url, path, line, 1));
       the_call << url;
+      the_call.should_eval() = true;
       return the_call;
     }
 

eval_apply.cpp

@@ -290,8 +290,11 @@ namespace Sass {
       } break;
 
       case Node::image_url: {
-        expr[0] = eval(expr[0], prefix, env, f_env, new_Node, ctx);
-        return expr;
+        Node base(eval(expr[0], prefix, env, f_env, new_Node, ctx));
+        Node prefix(new_Node(Node::identifier, base.path(), base.line(), Token::make(ctx.image_path)));
+        Node fullpath(new_Node(Node::concatenation, base.path(), base.line(), 2));
+        fullpath << prefix << base;
+        return fullpath;
       } break;
       
       case Node::function_call: {

sass_interface.cpp

@@ -59,6 +59,7 @@ extern "C" {
     using namespace Sass;
     try {
       Context cpp_ctx(c_ctx->options.include_paths);
+      cpp_ctx.image_path = c_ctx->options.image_path;
       // Document doc(0, c_ctx->input_string, cpp_ctx);
       Document doc(Document::make_from_source_chars(cpp_ctx, c_ctx->source_string));
       c_ctx->output_string = process_document(doc, c_ctx->options.output_style);
@@ -95,6 +96,7 @@ extern "C" {
     try {
       Context cpp_ctx(c_ctx->options.include_paths);
       // Document doc(c_ctx->input_path, 0, cpp_ctx);
+      cpp_ctx.image_path = c_ctx->options.image_path;
       Document doc(Document::make_from_file(cpp_ctx, string(c_ctx->input_path)));
       // cerr << "MADE A DOC AND CONTEXT OBJ" << endl;
       // cerr << "REGISTRY: " << doc.context.registry.size() << endl;

sass_interface.h

@@ -10,6 +10,7 @@ extern "C" {
 struct sass_options {
   int output_style;
   char* include_paths;
+  char* image_path;
 };
 
 struct sass_context {