spatnav: Allow focus move to a close-by not-fully-aligned node over a distant but fully-aligned nod…

Source/core/page/SpatialNavigation.cpp

Index: Source/core/page/SpatialNavigation.cpp
diff --git a/Source/core/page/SpatialNavigation.cpp b/Source/core/page/SpatialNavigation.cpp
index e9ea56911a233c090ba660d29a03419265d2e80c..852b27ebbbc203a7ffa0c4184d8c48eda1aa370a 100644
--- a/Source/core/page/SpatialNavigation.cpp
+++ b/Source/core/page/SpatialNavigation.cpp
@@ -59,7 +59,6 @@ FocusCandidate::FocusCandidate(Node* node, FocusType type)
     , focusableNode(nullptr)
     , enclosingScrollableBox(nullptr)
     , distance(maxDistance())
-    , alignment(None)
     , isOffscreen(true)
     , isOffscreenAfterScrolling(true)
 {
@@ -644,7 +643,6 @@ void distanceDataForNode(FocusType type, const FocusCandidate& current, FocusCan
     if (areElementsOnSameLine(current, candidate)) {
         if ((type == FocusTypeUp && current.rect.y() > candidate.rect.y()) || (type == FocusTypeDown && candidate.rect.y() > current.rect.y())) {
             candidate.distance = 0;
-            candidate.alignment = Full;
             return;
         }
     }
@@ -690,7 +688,18 @@ void distanceDataForNode(FocusType type, const FocusCandidate& current, FocusCan
     candidate.distance = sqrt(euclidianDistancePow2) + navigationAxisDistance+ orthogonalAxisDistance * 2 - sqrt(overlap);
 
     LayoutSize viewSize = LayoutSize(candidate.visibleNode->document().page()->deprecatedLocalMainFrame()->view()->visibleContentRect().size());
-    candidate.alignment = alignmentForRects(type, currentRect, nodeRect, viewSize);
+    RectsAlignment alignment = alignmentForRects(type, currentRect, nodeRect, viewSize);

[fs, 2014/12/15 11:36:09]

Should the weights be applied to (one of) the components of the distance
calculation (above) rather than to the "compound expression"?

[c.shu, 2014/12/15 18:17:37]

The distance calculation at L688 is based on the spec. Then I did the hack based
on alignment result. The weights are determined by some experimental tests. It
will be great if we can come up a better algorithm and integrate with the
calculation above.

[fs, 2014/12/16 13:15:42]

The link at L687 does not lead to a spec - it leads to a note =) (see red box
just at the top of it.) That being said, it doesn't hurt to read the section
about the distance calculation to see the motivation for the different parts -
it could probably even help in this case.

I.e you may change this calculation any way you want - we're after all pretty
far into heuristics-land here.
The WICD distance calculation includes a weight already as I understand - the
'2' that's applied to |orthogonalAxisDistance|, so it feels like that could be a
good starting point for further tweaking.

+    if (alignment == None) {
+        if (type == FocusTypeLeft || type == FocusTypeRight)
+            candidate.distance *= 4;
+        else
+            candidate.distance *= 1.5;
+    } else if (alignment == Partial) {
+        if (type == FocusTypeLeft || type == FocusTypeRight)
+            candidate.distance *= 2;
+        else
+            candidate.distance *= 1.2;
+    }
 }
 
 bool canBeScrolledIntoView(FocusType type, const FocusCandidate& candidate)