Fix resizing problems with DashDocDisplay

- Handle non-uniform child heights properly - use a constant
  grid size as the maximum of all child heights; with the
  previous code, the children might not line up in the two
  columns and the last item could be lost if the second column
  was taller than the first column.

- Call set_skip_paint(child, false) on children that we do
  want visible to override any previous hiding of that child.

- Correctly handle the DashDocDisplay not being allocated at 0, 0;
  children should be allocated starting at 0, 0, not at origin
  of the allocation box passed in.

- Remove an unused skipPaint variable.

https://bugzilla.gnome.org/show_bug.cgi?id=608801

js/ui/docDisplay.js

@@ -357,34 +357,37 @@ DashDocDisplay.prototype = {
     _getPreferredHeight: function(actor, forWidth, alloc) {
         let children = actor.get_children();
 
-        // Two columns, where we go vertically down first.  So just take
+        // The width of an item is our allocated width, minus spacing, divided in half.
-        // the height of half of the children as our preferred height.
+        this._itemWidth = Math.floor((forWidth - DEFAULT_SPACING) / 2);
+
+        let maxNatural = 0;
+        for (let i = 0; i < children.length; i++) {
+            let child = children[i];
+            let [minSize, naturalSize] = child.get_preferred_height(this._itemWidth);
+            maxNatural = Math.max(maxNatural, naturalSize);
+        }
+
+        this._itemHeight = maxNatural;
 
         let firstColumnChildren = Math.ceil(children.length / 2);
-
+        alloc.natural_size = (firstColumnChildren * maxNatural +
-        let natural = 0;
+                              (firstColumnChildren - 1) * DEFAULT_SPACING);
-        for (let i = 0; i < firstColumnChildren; i++) {
-            let child = children[i];
-            let [minSize, naturalSize] = child.get_preferred_height(-1);
-            natural += naturalSize;
-
-            if (i > 0 && i < children.length - 1) {
-                natural += DEFAULT_SPACING;
-            }
-        }
-        alloc.natural_size = natural;
     },
 
     _allocate: function(actor, box, flags) {
         let width = box.x2 - box.x1;
         let height = box.y2 - box.y1;
 
+        // Make sure this._itemWidth/Height have been computed, even
+        // if the parent actor didn't check our size before allocating.
+        // (Not clear if that is required or not as a Clutter
+        // invariant; this is safe and cheap because of caching.)
+        actor.get_preferred_height(width);
+
         let children = actor.get_children();
 
-        // The width of an item is our allocated width, minus spacing, divided in half.
+        let x = 0;
-        let itemWidth = Math.floor((width - DEFAULT_SPACING) / 2);
+        let y = 0;
-        let x = box.x1;
-        let y = box.y1;
         let columnIndex = 0;
         let i = 0;
         // Loop over the children, going vertically down first.  When we run
@@ -393,9 +396,7 @@ DashDocDisplay.prototype = {
         while (i < children.length) {
             let child = children[i];
 
-            let [minSize, naturalSize] = child.get_preferred_height(-1);
+            if (y + this._itemHeight > box.y2) {
-
-            if (y + naturalSize > box.y2) {
                 // Is this the second column, or we're in
                 // the first column and can't even fit one
                 // item?  In that case, break.
@@ -404,9 +405,9 @@ DashDocDisplay.prototype = {
                 }
                 // Set x to the halfway point.
                 columnIndex += 1;
-                x = x + itemWidth + DEFAULT_SPACING;
+                x = x + this._itemWidth + DEFAULT_SPACING;
                 // And y is back to the top.
-                y = box.y1;
+                y = 0;
                 // Retry this same item, now that we're in the second column.
                 // By looping back to the top here, we re-test the size
                 // again for the second column.
@@ -416,13 +417,13 @@ DashDocDisplay.prototype = {
             let childBox = new Clutter.ActorBox();
             childBox.x1 = x;
             childBox.y1 = y;
-            childBox.x2 = childBox.x1 + itemWidth;
+            childBox.x2 = childBox.x1 + this._itemWidth;
-            childBox.y2 = y + naturalSize;
+            childBox.y2 = y + this._itemHeight;
 
             y = childBox.y2 + DEFAULT_SPACING;
 
-            child.show();
             child.allocate(childBox, flags);
+            this.actor.set_skip_paint(child, false);
 
             i++;
         }
@@ -438,7 +439,6 @@ DashDocDisplay.prototype = {
             this._checkDocExistence = false;
         }
 
-        let skipPaint = [];
         for (; i < children.length; i++)
             this.actor.set_skip_paint(children[i], true);
     },