diff --git a/TODO b/TODO
index 0184f18..d670acb 100644
--- a/TODO
+++ b/TODO
@@ -1,3 +1,5 @@
+check fontforge with pkg-config first
+
 bug found in baidu & github & mail
 
 argument auto-completion
diff --git a/src/HTMLRenderer/LineBuffer.cc b/src/HTMLRenderer/LineBuffer.cc
index 10f8816..a999a07 100644
--- a/src/HTMLRenderer/LineBuffer.cc
+++ b/src/HTMLRenderer/LineBuffer.cc
@@ -17,14 +17,30 @@ using std::max;
 using std::vector;
 using std::ostream;
 
+// debug
+GfxFont * debug_font;
+double debug_width;
+
 void HTMLRenderer::LineBuffer::reset(GfxState * state)
 {
+    //debug
+    debug_font = state->getFont();
+
     state->transform(state->getCurX(), state->getCurY(), &x, &y);
     tm_id = renderer->cur_tm_id;
 }
 
 void HTMLRenderer::LineBuffer::append_unicodes(const Unicode * u, int l)
 {
+    //debug
+    if(text.size() == 0)
+    {
+        if(debug_font->isCIDFont())
+            debug_width = 0;
+        else
+            debug_width = dynamic_cast<Gfx8BitFont*>(debug_font)->getWidth(u[0]);
+    }
+
     text.insert(text.end(), u, u+l);
 }
 
@@ -150,6 +166,12 @@ void HTMLRenderer::LineBuffer::flush(void)
 
         size_t next_text_idx = min(cur_state_iter->start_idx, cur_offset_iter->start_idx);
 
+        {
+            double w;
+            auto wid = renderer->install_whitespace(debug_width, w);
+            out << "<span class=\"_ _" << wid << "\">"  << "</span>";
+        }
+
         outputUnicodes(out, (&text.front()) + cur_text_idx, next_text_idx - cur_text_idx);
         cur_text_idx = next_text_idx;
     }