3 files changed, 19 insertions, 7 deletions

diff --git a/src/gmdocument.c b/src/gmdocument.c
index b9832f38..6ed628de 100644
--- a/src/gmdocument.c
+++ b/src/gmdocument.c
@@ -82,6 +82,7 @@ struct Impl_GmDocument {
     iString   url;         /* for resolving relative links */
     iString   localHost;
     iInt2     size;
+    int       outsideMargin;
     iArray    layout; /* contents of source, laid out in document space */
     iPtrArray links;
     enum iGmDocumentBanner bannerType;
@@ -896,6 +897,12 @@ static void doLayout_GmDocument_(iGmDocument *d) {
                 pos.y += margin;
                 run.bounds.pos = pos;
                 run.bounds.size.x = d->size.x;
+                /* Extend the image to full width, including outside margin, if the viewport
+                   is narrow enough. */
+                if (d->outsideMargin < 5 * gap_UI) {
+                    run.bounds.size.x += d->outsideMargin * 2;
+                    run.bounds.pos.x  -= d->outsideMargin;
+                }                
                 const float aspect = (float) imgSize.y / (float) imgSize.x;
                 run.bounds.size.y = d->size.x * aspect;
                 run.visBounds = run.bounds;
@@ -990,6 +997,7 @@ void init_GmDocument(iGmDocument *d) {
     init_String(&d->url);
     init_String(&d->localHost);
     d->bannerType = siteDomain_GmDocumentBanner;
+    d->outsideMargin = 0;
     d->size = zero_I2();
     init_Array(&d->layout, sizeof(iGmRun));
     init_PtrArray(&d->links);
@@ -1543,8 +1551,9 @@ void setBanner_GmDocument(iGmDocument *d, enum iGmDocumentBanner type) {
     d->bannerType = type;
 }
 
-void setWidth_GmDocument(iGmDocument *d, int width) {
+void setWidth_GmDocument(iGmDocument *d, int width, int outsideMargin) {
     d->size.x = width;
+    d->outsideMargin = outsideMargin; /* distance to edge of the viewport */
     doLayout_GmDocument_(d); /* TODO: just flag need-layout and do it later */
 }
 
@@ -1698,7 +1707,7 @@ void setUrl_GmDocument(iGmDocument *d, const iString *url) {
     updateIconBasedOnUrl_GmDocument_(d);
 }
 
-void setSource_GmDocument(iGmDocument *d, const iString *source, int width,
+void setSource_GmDocument(iGmDocument *d, const iString *source, int width, int outsideMargin,
                           enum iGmDocumentUpdate updateType) {
 //    printf("[GmDocument] source update (%zu bytes), width:%d, final:%d\n",
 //           size_String(source), width, updateType == final_GmDocumentUpdate);
@@ -1713,7 +1722,7 @@ void setSource_GmDocument(iGmDocument *d, const iString *source, int width,
     if (isNormalized_GmDocument_(d)) {
         normalize_GmDocument(d);
     }
-    setWidth_GmDocument(d, width); /* re-do layout */
+    setWidth_GmDocument(d, width, outsideMargin); /* re-do layout */
 }
 
 void foldPre_GmDocument(iGmDocument *d, uint16_t preId) {
diff --git a/src/gmdocument.h b/src/gmdocument.h
index 9a7a70df..9f8ee2ef 100644
--- a/src/gmdocument.h
+++ b/src/gmdocument.h
@@ -174,11 +174,11 @@ enum iGmDocumentUpdate {
 void    setThemeSeed_GmDocument (iGmDocument *, const iBlock *seed);
 void    setFormat_GmDocument    (iGmDocument *, enum iSourceFormat format);
 void    setBanner_GmDocument    (iGmDocument *, enum iGmDocumentBanner type);
-void    setWidth_GmDocument     (iGmDocument *, int width);
+void    setWidth_GmDocument     (iGmDocument *, int width, int outsideMargin);
 void    redoLayout_GmDocument   (iGmDocument *);
 iBool   updateOpenURLs_GmDocument(iGmDocument *);
 void    setUrl_GmDocument       (iGmDocument *, const iString *url);
-void    setSource_GmDocument    (iGmDocument *, const iString *source, int width,
+void    setSource_GmDocument    (iGmDocument *, const iString *source, int width, int outsideMargin,
                                  enum iGmDocumentUpdate updateType);
 void    foldPre_GmDocument      (iGmDocument *, uint16_t preId);
 
diff --git a/src/ui/documentwidget.c b/src/ui/documentwidget.c
index e1be27c2..8de1162f 100644
--- a/src/ui/documentwidget.c
+++ b/src/ui/documentwidget.c
@@ -1054,9 +1054,12 @@ static void documentWasChanged_DocumentWidget_(iDocumentWidget *d) {
 
 void setSource_DocumentWidget(iDocumentWidget *d, const iString *source) {
     setUrl_GmDocument(d->doc, d->mod.url);
+    const int docWidth      = documentWidth_DocumentWidget_(d);
+    const int outsideMargin = (width_Widget(d) - docWidth) / 2;
     setSource_GmDocument(d->doc,
                          source,
-                         documentWidth_DocumentWidget_(d),
+                         docWidth,
+                         outsideMargin,
                          isFinished_GmRequest(d->request) ? final_GmDocumentUpdate
                                                           : partial_GmDocumentUpdate);
     documentWasChanged_DocumentWidget_(d);
@@ -2249,7 +2252,7 @@ static iBool updateDocumentWidthRetainingScrollPosition_DocumentWidget_(iDocumen
         /* TODO: First *fully* visible run? */
         voffset = visibleRange_DocumentWidget_(d).start - top_Rect(run->visBounds);
     }
-    setWidth_GmDocument(d->doc, newWidth);
+    setWidth_GmDocument(d->doc, newWidth, (width_Widget(d) - newWidth) / 2);
     documentRunsInvalidated_DocumentWidget_(d);
     if (runLoc && !keepCenter) {
         run = findRunAtLoc_GmDocument(d->doc, runLoc);