QGAL: Do not create sizeHint constraints for dependent anchors

Some anchors have their sizes linked directly to the size of
others. That is the case for instance with center anchors where
one half must have exactly the same size as the other.

To make that more clear, adding "dependency" info to AnchorData
and setting it accordingly. This is future proof in the sense
that if someday we are allowed to anchor to other items in terms
of percentages, like, anchor to 70% of an items' width, we would
also need this notion.

Knowing that, we no longer need to create size hint constraints for
the slave anchors, only for the master ones. The size of slave anchors
is enforced by the dependency constraint (sizeSlave = X * sizeMaster).

Signed-off-by: Eduardo M. Fleury <eduardo.fleury@openbossa.org>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@openbossa.org>

2 files changed, 25 insertions, 10 deletions

diff --git a/src/gui/graphicsview/qgraphicsanchorlayout_p.cpp b/src/gui/graphicsview/qgraphicsanchorlayout_p.cpp
index dbfce74159..ad7d6578f5 100644
--- a/src/gui/graphicsview/qgraphicsanchorlayout_p.cpp
+++ b/src/gui/graphicsview/qgraphicsanchorlayout_p.cpp
@@ -1080,12 +1080,14 @@ void QGraphicsAnchorLayoutPrivate::createCenterAnchors(
     c->variables.insert(data, 1.0);
     addAnchor_helper(item, firstEdge, item, centerEdge, data);
     data->isCenterAnchor = true;
+    data->dependency = AnchorData::Master;
     data->refreshSizeHints(0);
 
     data = new AnchorData;
     c->variables.insert(data, -1.0);
     addAnchor_helper(item, centerEdge, item, lastEdge, data);
     data->isCenterAnchor = true;
+    data->dependency = AnchorData::Slave;
     data->refreshSizeHints(0);
 
     itemCenterConstraints[orientation].append(c);
@@ -2075,19 +2077,18 @@ QList<QSimplexConstraint *> QGraphicsAnchorLayoutPrivate::constraintsFromSizeHin
     // Look for the layout edge. That can be either the first half in case the
     // layout is split in two, or the whole layout anchor.
     Orientation orient = Orientation(anchors.first()->orientation);
-    AnchorData *layoutEdge1 = NULL;
-    AnchorData *layoutEdge2 = NULL;
+    AnchorData *layoutEdge = NULL;
     if (layoutCentralVertex[orient]) {
-        layoutEdge1 = graph[orient].edgeData(layoutFirstVertex[orient], layoutCentralVertex[orient]);
-        layoutEdge2 = graph[orient].edgeData(layoutCentralVertex[orient], layoutLastVertex[orient]);
+        layoutEdge = graph[orient].edgeData(layoutFirstVertex[orient], layoutCentralVertex[orient]);
     } else {
-        layoutEdge1 = graph[orient].edgeData(layoutFirstVertex[orient], layoutLastVertex[orient]);
+        layoutEdge = graph[orient].edgeData(layoutFirstVertex[orient], layoutLastVertex[orient]);
+
         // If maxSize is less then "infinite", that means there are other anchors
         // grouped together with this one. We can't ignore its maximum value so we
         // set back the variable to NULL to prevent the continue condition from being
         // satisfied in the loop below.
-        if (layoutEdge1->maxSize < QWIDGETSIZE_MAX)
-            layoutEdge1 = NULL;
+        if (layoutEdge->maxSize < QWIDGETSIZE_MAX)
+            layoutEdge = NULL;
     }
 
     // For each variable, create constraints based on size hints
@@ -2096,6 +2097,12 @@ QList<QSimplexConstraint *> QGraphicsAnchorLayoutPrivate::constraintsFromSizeHin
     for (int i = 0; i < anchors.size(); ++i) {
         AnchorData *ad = anchors[i];
 
+        // Anchors that have their size directly linked to another one don't need constraints
+        // For exammple, the second half of an item has exactly the same size as the first half
+        // thus constraining the latter is enough.
+        if (ad->dependency == AnchorData::Slave)
+            continue;
+
         if ((ad->minSize == ad->maxSize) || qFuzzyCompare(ad->minSize, ad->maxSize)) {
             QSimplexConstraint *c = new QSimplexConstraint;
             c->variables.insert(ad, 1.0);
@@ -2113,7 +2120,7 @@ QList<QSimplexConstraint *> QGraphicsAnchorLayoutPrivate::constraintsFromSizeHin
             // We avoid adding restrictions to the layout internal anchors. That's
             // to prevent unnecessary fair distribution from happening due to this
             // artificial restriction.
-            if ((ad == layoutEdge1) || (ad == layoutEdge2))
+            if (ad == layoutEdge)
                 continue;
 
             c = new QSimplexConstraint;
@@ -2128,7 +2135,7 @@ QList<QSimplexConstraint *> QGraphicsAnchorLayoutPrivate::constraintsFromSizeHin
     // If no upper boundary restriction was added, add one to avoid unbounded problem
     if (unboundedProblem) {
         QSimplexConstraint *c = new QSimplexConstraint;
-        c->variables.insert(layoutEdge1, 1.0);
+        c->variables.insert(layoutEdge, 1.0);
         c->constant = QWIDGETSIZE_MAX;
         c->ratio = QSimplexConstraint::LessOrEqual;
         anchorConstraints += c;
diff --git a/src/gui/graphicsview/qgraphicsanchorlayout_p.h b/src/gui/graphicsview/qgraphicsanchorlayout_p.h
index 7d7bdb6d32..2f0237c263 100644
--- a/src/gui/graphicsview/qgraphicsanchorlayout_p.h
+++ b/src/gui/graphicsview/qgraphicsanchorlayout_p.h
@@ -150,6 +150,12 @@ struct AnchorData : public QSimplexVariable {
         Parallel
     };
 
+    enum Dependency {
+        Independent = 0,
+        Master,
+        Slave
+    };
+
     AnchorData()
         : QSimplexVariable(), item(0), from(0), to(0),
           minSize(0), prefSize(0), expSize(0), maxSize(0),
@@ -157,7 +163,8 @@ struct AnchorData : public QSimplexVariable {
           sizeAtExpanding(0), sizeAtMaximum(0),
           graphicsAnchor(0), skipInPreferred(0),
           type(Normal), hasSize(true), isLayoutAnchor(false),
-          isCenterAnchor(false), orientation(0) {}
+          isCenterAnchor(false), orientation(0),
+          dependency(Independent) {}
 
     virtual void updateChildrenSizes() {}
     virtual bool refreshSizeHints(const QLayoutStyleInfo *styleInfo);
@@ -212,6 +219,7 @@ struct AnchorData : public QSimplexVariable {
     uint isLayoutAnchor : 1;  // if this anchor is an internal layout anchor
     uint isCenterAnchor : 1;
     uint orientation : 1;
+    uint dependency : 2;      // either Independent, Master or Slave
 };
 
 #ifdef QT_DEBUG