Fixing the painting of the overlap area between tabs. Not part of the build.

gfx/src/gtk/gtkdrawing.c

@@ -413,22 +413,53 @@ moz_gtk_progress_chunk_paint(GdkWindow* window, GtkStyle* style,
 
 void
 moz_gtk_tab_paint(GdkWindow* window, GtkStyle* style, GdkRectangle* rect,
-                  GdkRectangle* cliprect, GtkTabType type)
+                  GdkRectangle* cliprect, gint flags)
 {
+  /*
+   * In order to get the correct shadows and highlights, GTK paints tabs
+   * right-to-left (end-to-beginning, to be generic), leaving out the
+   * active tab, and then paints the current tab once everything else is
+   * painted.  In addition, GTK uses a 2-pixel overlap between adjacent tabs
+   * (this value is hard-coded in gtknotebook.c).  For purposes of mapping to
+   * gecko's frame positions, we put this overlap on the far edge of the frame
+   * (i.e., for a horizontal/top tab strip, we shift the left side of each tab
+   * 2px to the left, into the neighboring tab's frame rect.  The right 2px
+   * of a tab's frame will be referred to as the "overlap area".
+   *
+   * Since we can't guarantee painting order with gecko, we need to manage
+   * the overlap area manually. There are three types of tab boundaries we need to handle:
+   *
+   *   * two non-active tabs: In this case, we just have both tabs paint normally.
+   *
+   *   * non-active to active tab: Here, we need the tab on the left to paint itself
+   *                               normally, then paint the edge of the active tab
+   *                               in its overlap area.
+   *
+   *   * active to non-active tab: In this case, we just have both tabs paint normally.
+   *
+   * We need to make an exception for the first tab - since there is no tab to the
+   * left to paint the overlap area, we do _not_ shift the tab left by 2px.
+   */
+
+  if (!(flags & MOZ_GTK_TAB_FIRST)) {
+    rect->x -= 2;
+    rect->width += 2;
+  }
+
   gtk_paint_extension(style, window,
-                      (type == kTabSelected ? GTK_STATE_NORMAL : GTK_STATE_ACTIVE),
+                      ((flags & MOZ_GTK_TAB_SELECTED) ? GTK_STATE_NORMAL : GTK_STATE_ACTIVE),
                       GTK_SHADOW_OUT, cliprect, gTabWidget, "tab", rect->x,
                       rect->y, rect->width, rect->height, GTK_POS_BOTTOM);
 
-  /* Here is the sleazy hack for before/after selected tab */
-  if (type == kTabBeforeSelected)
-    gtk_paint_extension(style, window, GTK_STATE_NORMAL, GTK_SHADOW_OUT,
-                        cliprect, gTabWidget, "tab", rect->x + rect->width,
-                        rect->y, rect->width, rect->height, GTK_POS_BOTTOM);
-  else if (type == kTabAfterSelected)
-    gtk_paint_extension(style, window, GTK_STATE_NORMAL, GTK_SHADOW_OUT,
-                        cliprect, gTabWidget, "tab", rect->x - rect->width,
-                        rect->y, rect->width, rect->height, GTK_POS_BOTTOM);
+  if (flags & MOZ_GTK_TAB_BEFORE_SELECTED) {
+    gboolean before_selected = ((flags & MOZ_GTK_TAB_BEFORE_SELECTED) != 0);
+    cliprect->y -= 2;
+    cliprect->height += 2;
+    gtk_paint_extension(style, window, GTK_STATE_NORMAL, GTK_SHADOW_OUT, cliprect,
+                        gTabWidget, "tab", rect->x + rect->width - 2,
+                        rect->y - (2 * before_selected), rect->width,
+                        rect->height + (2 * before_selected), GTK_POS_BOTTOM);
+  }
 }
 
 void

gfx/src/gtk/gtkdrawing.h

@@ -56,12 +56,10 @@ typedef struct {
   PRPackedBool canDefault;
 } GtkWidgetState;
 
-typedef enum {
-  kTabNormal,
-  kTabBeforeSelected,
-  kTabSelected,
-  kTabAfterSelected
-} GtkTabType;
+/* flags for tab state */
+#define MOZ_GTK_TAB_FIRST           (1<<0)
+#define MOZ_GTK_TAB_BEFORE_SELECTED (1<<1)
+#define MOZ_GTK_TAB_SELECTED        (1<<2)
 
 void
 moz_gtk_button_paint(GdkWindow* window, GtkStyle* style, GdkRectangle* rect,
@@ -132,7 +130,7 @@ moz_gtk_progress_chunk_paint(GdkWindow* window, GtkStyle* style,
 
 void
 moz_gtk_tab_paint(GdkWindow* window, GtkStyle* style, GdkRectangle* rect,
-                  GdkRectangle* cliprect, GtkTabType type);
+                  GdkRectangle* cliprect, gint flags);
 
 void
 moz_gtk_tabpanels_paint(GdkWindow* window, GtkStyle* style,

gfx/src/gtk/nsNativeThemeGTK.cpp

@@ -80,6 +80,7 @@ nsNativeThemeGTK::nsNativeThemeGTK()
   mInputCheckedAtom = do_GetAtom("_moz-input-checked");
   mInputAtom = do_GetAtom("input");
   mFocusedAtom = do_GetAtom("focused");
+  mFirstTabAtom = do_GetAtom("first-tab");
 }
 
 nsNativeThemeGTK::~nsNativeThemeGTK() {
@@ -364,24 +365,20 @@ nsNativeThemeGTK::DrawWidgetBackground(nsIRenderingContext* aContext,
   case NS_THEME_TAB_RIGHT_EDGE:
     {
       EnsureTabWidget();
-      GtkTabType tab_type;
-      switch (aWidgetType) {
-        case NS_THEME_TAB:
-          {
-            PRBool isSelected = CheckBooleanAttr(aFrame, mSelectedAtom);
-            tab_type = (isSelected ? kTabSelected : kTabNormal);
-          }
-          break;
-        case NS_THEME_TAB_LEFT_EDGE:
-          tab_type = kTabBeforeSelected;
-          break;
-        case NS_THEME_TAB_RIGHT_EDGE:
-          tab_type = kTabAfterSelected;
-          break;
-      }
+      gint tab_flags = 0;
+
+      if (aWidgetType == NS_THEME_TAB && CheckBooleanAttr(aFrame, mSelectedAtom))
+        tab_flags |= MOZ_GTK_TAB_SELECTED;
+      else if (aWidgetType == NS_THEME_TAB_LEFT_EDGE)
+        tab_flags |= MOZ_GTK_TAB_BEFORE_SELECTED;
+
+      nsCOMPtr<nsIContent> content;
+      aFrame->GetContent(getter_AddRefs(content));
+      if (content->HasAttr(kNameSpaceID_None, mFirstTabAtom))
+        tab_flags |= MOZ_GTK_TAB_FIRST;
 
       moz_gtk_tab_paint(window, gTabWidget->style, &gdk_rect, &gdk_clip,
-                        tab_type);
+                        tab_flags);
       break;
     }
   }

gfx/src/gtk/nsNativeThemeGTK.h

@@ -109,6 +109,7 @@ private:
   nsCOMPtr<nsIAtom> mInputCheckedAtom;
   nsCOMPtr<nsIAtom> mInputAtom;
   nsCOMPtr<nsIAtom> mFocusedAtom;
+  nsCOMPtr<nsIAtom> mFirstTabAtom;
 
   GtkWidget* mProtoLayout;
 };