Update to trunk r13580

(bzr r13341.1.255)

12 files changed, 220 insertions, 36 deletions

diff --git a/src/extension/extension.cpp b/src/extension/extension.cpp
index 06e35ff3e..6a22eb585 100644
--- a/src/extension/extension.cpp
+++ b/src/extension/extension.cpp
@@ -112,8 +112,13 @@ Extension::Extension (Inkscape::XML::Node * in_repr, Implementation::Implementat
                 _deps.push_back(new Dependency(child_repr));
             } /* dependency */
             if (!strcmp(chname, "script")) {
-                _deps.push_back(new Dependency(child_repr->firstChild()));
-            } /* check command as a dependency (see LP #505920)  */
+                for (Inkscape::XML::Node *child = child_repr->firstChild(); child != NULL ; child = child->next()) {
+                    if (child->type() == Inkscape::XML::ELEMENT_NODE) {
+                        _deps.push_back(new Dependency(child));
+                        break;
+                    } /* skip non-element nodes (see LP #1372200) */
+                }
+            } /* check command as a dependency (see LP #505920) */
             if (!strcmp(chname, "options")) {
                 silent = !strcmp( child_repr->attribute("silent"), "true" );
             }
diff --git a/src/extension/internal/emf-inout.cpp b/src/extension/internal/emf-inout.cpp
index 9a5a78a34..4b070cbaa 100644
--- a/src/extension/internal/emf-inout.cpp
+++ b/src/extension/internal/emf-inout.cpp
@@ -63,6 +63,7 @@ namespace Internal {
 
 static uint32_t ICMmode = 0;  // not used yet, but code to read it from EMF implemented
 static uint32_t BLTmode = 0;
+float           faraway = 10000000; // used in "exclude" clips, hopefully well outside any real drawing!
 
 Emf::Emf (void) // The null constructor
 {
@@ -1040,13 +1041,30 @@ Emf::pix_to_abs_size(PEMF_CALLBACK_DATA d, double px)
     return ppx;
 }
 
-/* returns "x,y" (without the quotes) in inkscape coordinates for a pair of EMF x,y coordinates
+/* snaps coordinate pairs made up of values near +/-faraway, +/-faraway to exactly faraway.
+   This eliminates coordinate drift on repeated clipping cycles which use exclude.  
+   It should not affect internals of normal drawings because the value of faraway is so large.
+*/
+void
+Emf::snap_to_faraway_pair(double *x, double *y)
+{
+    if((abs(abs(*x) - faraway)/faraway <= 1e-4) && (abs(abs(*y) - faraway)/faraway <= 1e-4)){
+        *x = (*x > 0 ? faraway : -faraway);
+        *y = (*y > 0 ? faraway : -faraway);
+    }
+}
+
+/* returns "x,y" (without the quotes) in inkscape coordinates for a pair of EMF x,y coordinates.
+   Since exclude clip can go through here, it calls snap_to_faraway_pair for numerical stability.
 */
 std::string Emf::pix_to_xy(PEMF_CALLBACK_DATA d, double x, double y){
     std::stringstream cxform;
-    cxform << pix_to_x_point(d,x,y);
+    double tx = pix_to_x_point(d,x,y);
+    double ty = pix_to_y_point(d,x,y);
+    snap_to_faraway_pair(&tx,&ty);
+    cxform << tx;
     cxform << ",";
-    cxform << pix_to_y_point(d,x,y);
+    cxform << ty;
     return(cxform.str());
 }
 
@@ -2221,7 +2239,6 @@ std::cout << "BEFORE DRAW"
             U_RECTL rc = pEmr->rclClip;
 
             SVGOStringStream tmp_path;
-            float faraway = 10000000; // hopefully well outside any real drawing!
             //outer rect, clockwise 
             tmp_path << "M " <<  faraway << "," <<  faraway << " ";
             tmp_path << "L " <<  faraway << "," << -faraway << " ";
@@ -3466,6 +3483,8 @@ Emf::open( Inkscape::Extension::Input * /*mod*/, const gchar *uri )
         return NULL;
     }
 
+    d.dc[0].font_name = strdup("Arial"); // Default font, set only on lowest level, it copies up from there EMF spec says device can pick whatever it wants
+
     // set up the size default for patterns in defs.  This might not be referenced if there are no patterns defined in the drawing.
 
     d.defs += "\n";
@@ -3513,7 +3532,7 @@ Emf::open( Inkscape::Extension::Input * /*mod*/, const gchar *uri )
 
     d.dc[0].style.stroke_dasharray.values.clear();
 
-    for(int i=0; i<=d.level;i++){
+    for(int i=0; i<=EMF_MAX_DC; i++){
       if(d.dc[i].font_name)free(d.dc[i].font_name);
     }
 
diff --git a/src/extension/internal/emf-inout.h b/src/extension/internal/emf-inout.h
index 302d5c474..c64299093 100644
--- a/src/extension/internal/emf-inout.h
+++ b/src/extension/internal/emf-inout.h
@@ -65,7 +65,7 @@ typedef struct emf_device_context {
         textAlign(0)
         // worldTransform, cur
     {
-        font_name = strdup("Arial"); // Default font, EMF spec says device can pick whatever it wants
+        font_name = NULL;
         sizeWnd  = sizel_set( 0.0, 0.0 );
         sizeView = sizel_set( 0.0, 0.0 );
         winorg  = point32_set( 0.0, 0.0 );
@@ -218,6 +218,7 @@ protected:
     static double      pix_to_x_point(PEMF_CALLBACK_DATA d, double px, double py);
     static double      pix_to_y_point(PEMF_CALLBACK_DATA d, double px, double py);
     static double      pix_to_abs_size(PEMF_CALLBACK_DATA d, double px);
+    static void        snap_to_faraway_pair(double *x, double *y);
     static std::string pix_to_xy(PEMF_CALLBACK_DATA d, double x, double y);
     static void        select_pen(PEMF_CALLBACK_DATA d, int index);
     static void        select_extpen(PEMF_CALLBACK_DATA d, int index);
diff --git a/src/extension/internal/emf-print.cpp b/src/extension/internal/emf-print.cpp
index e054829b5..0f43fbca1 100644
--- a/src/extension/internal/emf-print.cpp
+++ b/src/extension/internal/emf-print.cpp
@@ -55,6 +55,7 @@
 #include "sp-radial-gradient.h"
 #include "sp-linear-gradient.h"
 #include "display/cairo-utils.h"
+#include "sp-shape.h"
 
 #include "splivarot.h"             // pieces for union on shapes
 #include "2geom/svg-path-parser.h" // to get from SVG text to Geom::Path
@@ -143,6 +144,7 @@ unsigned int PrintEmf::begin(Inkscape::Extension::Print *mod, SPDocument *doc)
     // width and height in px
     _width  = doc->getWidth().value("px");
     _height = doc->getHeight().value("px");
+    _doc_unit_scale = Inkscape::Util::Quantity::convert(1, (doc->getDefaultUnit()), "px");
 
     // initialize a few global variables
     hbrush = hbrushOld = hpen = 0;
@@ -298,6 +300,7 @@ unsigned int PrintEmf::begin(Inkscape::Extension::Print *mod, SPDocument *doc)
 
 unsigned int PrintEmf::finish(Inkscape::Extension::Print * /*mod*/)
 {
+    do_clip_if_present(NULL);  // Terminate any open clip.
     char *rec;
     if (!et) {
         return 0;
@@ -969,19 +972,145 @@ U_TRIVERTEX PrintEmf::make_trivertex(Geom::Point Pt, U_COLORREF uc){
     return(tv);
 }
 
+/*  Examine clip.  If there is a (new) one then apply it.  If there is one and it is the
+    same as the preceding one, leave the preceding one active.  If style is NULL
+    terminate the current clip, if any, and return.
+*/
+void  PrintEmf::do_clip_if_present(SPStyle const *style){
+    char *rec;
+    static SPClipPath *scpActive = NULL;
+    if(!style){
+        if(scpActive){  // clear the existing clip
+            rec = U_EMRRESTOREDC_set(-1);
+            if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
+                g_error("Fatal programming error in PrintEmf::fill at U_EMRRESTOREDC_set");
+            }
+            scpActive=NULL;
+        }
+    } else {
+        /* The current implementation converts only one level of clipping.  If there were more
+           clips further up the stack they should be combined with the pathvector using "and".  Since this
+           comes up rarely, and would involve a lot of searching (all the way up the stack for every
+           draw operation), it has not yet been implemented.  
+
+           Note, to debug this section of code use print statements on sp_svg_write_path(combined_pathvector).
+        */
+        /*  find the first clip_ref at object or up the stack.  There may not be one. */
+        SPClipPath *scp = NULL;
+        SPItem *item = SP_ITEM(style->object);
+        while(1) {
+            scp = (item->clip_ref ? item->clip_ref->getObject() : NULL);
+            if(scp)break;
+            item = SP_ITEM(item->parent);
+            if(!item || SP_IS_ROOT(item))break; // this will never be a clipping path
+        }
+        
+        if(scp != scpActive){  // change or remove the clipping
+            if(scpActive){  // clear the existing clip
+                rec = U_EMRRESTOREDC_set(-1);
+                if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
+                    g_error("Fatal programming error in PrintEmf::fill at U_EMRRESTOREDC_set");
+                }
+                scpActive = NULL;
+            }
+
+            if (scp) {  // set the new clip
+                /* because of units and who knows what other transforms that might be applied above we
+                   need the full transform all the way to the root.
+                */
+                Geom::Affine tf = item->transform;
+                SPItem *scan_item = item;
+                while(1) {
+                   scan_item = SP_ITEM(scan_item->parent);
+                   if(!scan_item)break;
+                   tf *= scan_item->transform;
+                }
+                tf *= Geom::Scale(_doc_unit_scale);;  // Transform must be in PIXELS, no matter what the document unit is.
+
+                /* find the clipping path */
+                Geom::PathVector combined_pathvector;
+                Geom::Affine tfc;   // clipping transform, generally not the same as item transform
+                for(item = SP_ITEM(scp->firstChild()); item; item=SP_ITEM(item->getNext())){
+                    if (SP_IS_GROUP(item)) {      // not implemented 
+                        // return sp_group_render(item);
+                        combined_pathvector = merge_PathVector_with_group(combined_pathvector, item, tfc);
+                    } else if (SP_IS_SHAPE(item)) {                
+                        combined_pathvector = merge_PathVector_with_shape(combined_pathvector, item, tfc);
+                    } else {        // not implemented           
+                    }                                              
+                }
+
+                if (!combined_pathvector.empty()) { // if clipping path isn't empty, define EMF clipping record
+                    scpActive = scp;    // remember for next time
+                    // the sole purpose of this SAVEDC is to let us clear the clipping region later.
+                    rec = U_EMRSAVEDC_set();
+                    if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
+                        g_error("Fatal programming error in PrintEmf::image at U_EMRSAVEDC_set");
+                    }
+                    (void) draw_pathv_to_EMF(combined_pathvector, tf);
+                    rec = U_EMRSELECTCLIPPATH_set(U_RGN_OR);
+                    if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
+                        g_error("Fatal programming error in PrintEmf::do_clip_if_present at U_EMRSELECTCLIPPATH_set");
+                    }
+                }
+                else {
+                    scpActive = NULL; // no valid path available to draw, so no DC was saved, so no signal to restore
+                }
+            } // change or remove clipping
+        } // scp exists
+    } // style exists
+}
+
+Geom::PathVector PrintEmf::merge_PathVector_with_group(Geom::PathVector const &combined_pathvector, SPItem const *item, const Geom::Affine &transform)
+{
+    Geom::PathVector new_combined_pathvector;
+    if(!SP_IS_GROUP(item))return(new_combined_pathvector);  // sanity test, only a group should be passed in, return empty if something else happens
+
+    new_combined_pathvector = combined_pathvector;
+    SPGroup *group = SP_GROUP(item);
+    Geom::Affine tfc = item->transform * transform;
+    for(SPItem *item = SP_ITEM(group->firstChild()); item; item=SP_ITEM(item->getNext())){
+        if (SP_IS_GROUP(item)) {
+            new_combined_pathvector = merge_PathVector_with_group(new_combined_pathvector, item, tfc); // could be endlessly recursive on a badly formed SVG
+        } else if (SP_IS_SHAPE(item)) {                
+            new_combined_pathvector = merge_PathVector_with_shape(new_combined_pathvector, item, tfc);
+        } else {        // not implemented           
+        }                                              
+    }
+    return new_combined_pathvector;
+}
+
+Geom::PathVector PrintEmf::merge_PathVector_with_shape(Geom::PathVector const &combined_pathvector, SPItem const *item, const Geom::Affine &transform)
+{
+    Geom::PathVector new_combined_pathvector;
+    if(!SP_IS_SHAPE(item))return(new_combined_pathvector);  // sanity test, only a shape should be passed in, return empty if something else happens
+
+    Geom::Affine tfc = item->transform * transform;
+    SPShape *shape = SP_SHAPE(item);
+    if (shape->_curve) {
+        Geom::PathVector const & new_vect = shape->_curve->get_pathvector();
+        if(combined_pathvector.empty()){
+            new_combined_pathvector = new_vect * tfc;
+        }
+        else {
+            new_combined_pathvector = sp_pathvector_boolop(new_vect * tfc, combined_pathvector, bool_op_union , (FillRule) fill_oddEven, (FillRule) fill_oddEven);
+        }
+    }
+    return new_combined_pathvector;
+}
+
 unsigned int PrintEmf::fill(
     Inkscape::Extension::Print * /*mod*/,
     Geom::PathVector const &pathv, Geom::Affine const & /*transform*/, SPStyle const *style,
     Geom::OptRect const &/*pbox*/, Geom::OptRect const &/*dbox*/, Geom::OptRect const &/*bbox*/)
 {
+    char *rec;
     using Geom::X;
     using Geom::Y;
-    
-    //SPItem *item = SP_ITEM(style->object);
-    //SPClipPath *scp = (item->clip_ref ? item->clip_ref->getObject() : NULL);
-
     Geom::Affine tf = m_tr_stack.top();
 
+    do_clip_if_present(style);  // If clipping is needed set it up
+
     use_fill   = true;
     use_stroke = false;
 
@@ -1095,7 +1224,6 @@ unsigned int PrintEmf::fill(
             }
         } else if (gv.mode == DRAW_LINEAR_GRADIENT) {
             if(is_Rect){
-                char *rec;
                 int gMode;
                 Geom::Point ul, ur, lr;
                 Geom::Point outUL, outLR; // UL,LR corners of a stop rectangle, in OUTPUT coordinates
@@ -1284,6 +1412,7 @@ unsigned int PrintEmf::stroke(
 
     char *rec = NULL;
     Geom::Affine tf = m_tr_stack.top();
+    do_clip_if_present(style);  // If clipping is needed set it up
 
     use_stroke = true;
     //  use_fill was set in ::fill, if it is needed
@@ -1568,12 +1697,14 @@ unsigned int PrintEmf::image(
     unsigned int h,      /** height of bitmap */
     unsigned int rs,     /** row stride (normally w*4) */
     Geom::Affine const &tf_rect,  /** affine transform only used for defining location and size of rect, for all other tranforms, use the one from m_tr_stack */
-    SPStyle const * /*style*/)  /** provides indirect link to image object */
+    SPStyle const *style)  /** provides indirect link to image object */
 {
     double x1, y1, dw, dh;
     char *rec = NULL;
     Geom::Affine tf = m_tr_stack.top();
 
+    do_clip_if_present(style);  // If clipping is needed set it up
+
     rec = U_EMRSETSTRETCHBLTMODE_set(U_COLORONCOLOR);
     if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
         g_error("Fatal programming error in PrintEmf::image at EMRHEADER");
@@ -1658,28 +1789,14 @@ unsigned int PrintEmf::image(
     return 0;
 }
 
-// may also be called with a simple_shape or an empty path, whereupon it just returns without doing anything
-unsigned int PrintEmf::print_pathv(Geom::PathVector const &pathv, const Geom::Affine &transform)
-{
-    Geom::Affine tf = transform;
-    char *rec = NULL;
-
-    simple_shape = print_simple_shape(pathv, tf);
-    if (simple_shape || pathv.empty()) {
-        if (use_fill) {
-            destroy_brush();    // these must be cleared even if nothing is drawn or hbrush,hpen fill up
-        }
-        if (use_stroke) {
-            destroy_pen();
-        }
-        return TRUE;
-    }
+unsigned int PrintEmf::draw_pathv_to_EMF(Geom::PathVector const &pathv, const Geom::Affine &transform) {
+    char *rec;
 
     /*  inkscape to EMF scaling is done below, but NOT the rotation/translation transform,
         that is handled by the EMF MODIFYWORLDTRANSFORM record
     */
-
-    Geom::PathVector pv = pathv_to_linear_and_cubic_beziers(pathv * tf);
+    
+    Geom::PathVector pv = pathv_to_linear_and_cubic_beziers(pathv * transform);
 
     rec = U_EMRBEGINPATH_set();
     if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
@@ -1781,6 +1898,27 @@ unsigned int PrintEmf::print_pathv(Geom::PathVector const &pathv, const Geom::Af
     if (!rec || emf_append((PU_ENHMETARECORD)rec, et, U_REC_FREE)) {
         g_error("Fatal programming error in PrintEmf::print_pathv at U_EMRENDPATH_set");
     }
+    return(0);
+}
+
+// may also be called with a simple_shape or an empty path, whereupon it just returns without doing anything
+unsigned int PrintEmf::print_pathv(Geom::PathVector const &pathv, const Geom::Affine &transform)
+{
+    Geom::Affine tf = transform;
+    char *rec = NULL;
+
+    simple_shape = print_simple_shape(pathv, tf);
+    if (simple_shape || pathv.empty()) {
+        if (use_fill) {
+            destroy_brush();    // these must be cleared even if nothing is drawn or hbrush,hpen fill up
+        }
+        if (use_stroke) {
+            destroy_pen();
+        }
+        return TRUE;
+    }
+
+    (void) draw_pathv_to_EMF(pathv, tf);
 
     // explicit FILL/STROKE commands are needed for each sub section of the path
     if (use_fill && !use_stroke) {
@@ -1819,6 +1957,7 @@ unsigned int PrintEmf::text(Inkscape::Extension::Print * /*mod*/, char const *te
         return 0;
     }
 
+    do_clip_if_present(style);  // If clipping is needed set it up
     char *rec = NULL;
     int ccount, newfont;
     int fix90n = 0;
diff --git a/src/extension/internal/emf-print.h b/src/extension/internal/emf-print.h
index 9a1251b38..5bad48de5 100644
--- a/src/extension/internal/emf-print.h
+++ b/src/extension/internal/emf-print.h
@@ -69,6 +69,10 @@ public:
 protected:
     static void  smuggle_adxkyrtl_out(const char *string, uint32_t **adx, double *ky, int *rtl, int *ndx, float scale);
 
+    void        do_clip_if_present(SPStyle const *style);
+    Geom::PathVector merge_PathVector_with_group(Geom::PathVector const &combined_pathvector, SPItem const *item, const Geom::Affine &transform);
+    Geom::PathVector merge_PathVector_with_shape(Geom::PathVector const &combined_pathvector, SPItem const *item, const Geom::Affine &transform);
+    unsigned int draw_pathv_to_EMF(Geom::PathVector const &pathv, const Geom::Affine &transform);
     Geom::Path  pathv_to_simple_polygon(Geom::PathVector const &pathv, int *vertices);
     Geom::Path  pathv_to_rect(Geom::PathVector const &pathv, bool *is_rect, double *angle);
     Geom::Point get_pathrect_corner(Geom::Path pathRect, double angle, int corner);
diff --git a/src/extension/internal/image-resolution.cpp b/src/extension/internal/image-resolution.cpp
index f092b21ef..e96fd6437 100644
--- a/src/extension/internal/image-resolution.cpp
+++ b/src/extension/internal/image-resolution.cpp
@@ -354,8 +354,15 @@ void ImageResolution::readmagick(char const *fn) {
         return;
     }
 
+    std::string const type = image.magick();
     x_ = image.xResolution();
     y_ = image.yResolution();
+
+// TODO: find out why the hell the following convertion is necessary
+    if (type == "BMP") {
+        x_ = Inkscape::Util::Quantity::convert(x_, "in", "cm");
+        y_ = Inkscape::Util::Quantity::convert(y_, "in", "cm");
+    }
     
     if (x_ != 0 && y_ != 0) {
         ok_ = true;
diff --git a/src/extension/internal/metafile-inout.cpp b/src/extension/internal/metafile-inout.cpp
index 534b33a30..824934b3e 100644
--- a/src/extension/internal/metafile-inout.cpp
+++ b/src/extension/internal/metafile-inout.cpp
@@ -222,7 +222,7 @@ void Metafile::setViewBoxIfMissing(SPDocument *doc) {
         prefs->setBool("/options/transform/pattern", true);
         prefs->setBool("/options/transform/gradient", true);
         
-        doc->getRoot()->scaleChildItemsRec(Geom::Scale(scale), Geom::Point(0, dh));
+        doc->getRoot()->scaleChildItemsRec(Geom::Scale(scale), Geom::Point(0, dh), true);
         Inkscape::UI::ShapeEditor::blockSetItem(false);
 
         // restore options
diff --git a/src/extension/internal/metafile-print.h b/src/extension/internal/metafile-print.h
index a21f9de58..d184b72b7 100644
--- a/src/extension/internal/metafile-print.h
+++ b/src/extension/internal/metafile-print.h
@@ -69,6 +69,8 @@ protected:
 
     double  _width;
     double  _height;
+    double  _doc_unit_scale;     // to pixels, regardless of the document units
+    
     U_RECTL  rc;
 
     uint32_t htextalignment;
diff --git a/src/extension/internal/wmf-inout.cpp b/src/extension/internal/wmf-inout.cpp
index c03e7efe0..72c1c8bd3 100644
--- a/src/extension/internal/wmf-inout.cpp
+++ b/src/extension/internal/wmf-inout.cpp
@@ -3063,6 +3063,8 @@ Wmf::open( Inkscape::Extension::Input * /*mod*/, const gchar *uri )
         return NULL;
     }
 
+    d.dc[0].font_name = strdup("Arial"); // Default font, set only on lowest level, it copies up from there WMF spec says device can pick whatever it wants
+
     // set up the size default for patterns in defs.  This might not be referenced if there are no patterns defined in the drawing.
 
     d.defs += "\n";
@@ -3105,7 +3107,7 @@ Wmf::open( Inkscape::Extension::Input * /*mod*/, const gchar *uri )
 
     d.dc[0].style.stroke_dasharray.values.clear();
 
-    for(int i=0; i<=d.level;i++){
+    for(int i=0; i<=WMF_MAX_DC; i++){
       if(d.dc[i].font_name)free(d.dc[i].font_name);
     }
 
diff --git a/src/extension/internal/wmf-inout.h b/src/extension/internal/wmf-inout.h
index 27ec14358..5a0a760dd 100644
--- a/src/extension/internal/wmf-inout.h
+++ b/src/extension/internal/wmf-inout.h
@@ -65,7 +65,7 @@ typedef struct wmf_device_context {
         textAlign(0)
         // worldTransform, cur
     {
-        font_name = strdup("Arial"); // Default font, WMF spec says device can pick whatever it wants
+        font_name = NULL;
         sizeWnd = point16_set( 0.0, 0.0 );
         sizeView = point16_set( 0.0, 0.0 );
         winorg = point16_set( 0.0, 0.0 );
diff --git a/src/extension/prefdialog.cpp b/src/extension/prefdialog.cpp
index af31f32b6..0ea15a5cd 100644
--- a/src/extension/prefdialog.cpp
+++ b/src/extension/prefdialog.cpp
@@ -90,6 +90,10 @@ PrefDialog::PrefDialog (Glib::ustring name, gchar const * help, Gtk::Widget * co
     if (_effect != NULL && !_effect->no_live_preview) {
         if (_param_preview == NULL) {
             XML::Document * doc = sp_repr_read_mem(live_param_xml, strlen(live_param_xml), NULL);
+            if (doc == NULL) {
+                std::cout << "Error encountered loading live parameter XML !!!" << std::endl;
+                return;
+            }
             _param_preview = Parameter::make(doc->root(), _effect);
         }
 
diff --git a/src/extension/system.cpp b/src/extension/system.cpp
index d02d801dc..5225f11ee 100644
--- a/src/extension/system.cpp
+++ b/src/extension/system.cpp
@@ -556,7 +556,7 @@ build_from_file(gchar const *filename)
 }
 
 /**
- * \return   The module created
+ * \return   The module created, or NULL if buffer is invalid
  * \brief    This function creates a module from a buffer holding an
  *           XML description.
  * \param    buffer  The buffer holding the XML description of the module.
@@ -568,6 +568,7 @@ Extension *
 build_from_mem(gchar const *buffer, Implementation::Implementation *in_imp)
 {
     Inkscape::XML::Document *doc = sp_repr_read_mem(buffer, strlen(buffer), INKSCAPE_EXTENSION_URI);
+    g_return_val_if_fail(doc != NULL, NULL);
     Extension *ext = build_from_reprdoc(doc, in_imp);
     Inkscape::GC::release(doc);
     return ext;