Bug 1176619 - [css-grid] Implement the "Maximize Tracks" algorithm. r=dholbert

layout/generic/nsGridContainerFrame.cpp

@@ -494,6 +494,55 @@ struct MOZ_STACK_CLASS nsGridContainerFrame::Tracks
     CopyPlanToLimit(aPlan, aGrowableTracks);
   }
 
+  /**
+   * Distribute aAvailableSize to the tracks.  This implements 12.6 at:
+   * http://dev.w3.org/csswg/css-grid/#algo-grow-tracks
+   */
+  void DistributeFreeSpace(nscoord aAvailableSize)
+  {
+    const uint32_t numTracks = mSizes.Length();
+    if (MOZ_UNLIKELY(numTracks == 0 || aAvailableSize <= 0)) {
+      return;
+    }
+    if (aAvailableSize == NS_UNCONSTRAINEDSIZE) {
+      for (TrackSize& sz : mSizes) {
+        sz.mBase = sz.mLimit;
+      }
+    } else {
+      // Compute free space and count growable tracks.
+      nscoord space = aAvailableSize;
+      uint32_t numGrowable = numTracks;
+      for (const TrackSize& sz : mSizes) {
+        space -= sz.mBase;
+        MOZ_ASSERT(sz.mBase <= sz.mLimit);
+        if (sz.mBase == sz.mLimit) {
+          --numGrowable;
+        }
+      }
+      // Distribute the free space evenly to the growable tracks. If not exactly
+      // divisable the remainder is added to the leading tracks.
+      while (space > 0 && numGrowable) {
+        nscoord spacePerTrack =
+          std::max<nscoord>(space / numGrowable, 1);
+        for (uint32_t i = 0; i < numTracks && space > 0; ++i) {
+          TrackSize& sz = mSizes[i];
+          if (sz.mBase == sz.mLimit) {
+            continue;
+          }
+          nscoord newBase = sz.mBase + spacePerTrack;
+          if (newBase >= sz.mLimit) {
+            space -= sz.mLimit - sz.mBase;
+            sz.mBase = sz.mLimit;
+            --numGrowable;
+          } else {
+            space -= spacePerTrack;
+            sz.mBase = newBase;
+          }
+        }
+      }
+    }
+  }
+
 #ifdef DEBUG
   void Dump() const
   {
@@ -1650,6 +1699,9 @@ nsGridContainerFrame::CalculateTrackSizes(GridReflowState&   aState,
   aState.mCols.ResolveIntrinsicSize(aState, mGridItems, colFunctions,
                                     &GridArea::mCols, colPercentageBasis,
                                     aConstraint);
+  if (aConstraint != nsLayoutUtils::MIN_ISIZE) {
+    aState.mCols.DistributeFreeSpace(aContentBox.ISize(wm));
+  }
 
   aState.mRows.mSizes.SetLength(mGridRowEnd);
   PodZero(aState.mRows.mSizes.Elements(), aState.mRows.mSizes.Length());
@@ -1663,6 +1715,9 @@ nsGridContainerFrame::CalculateTrackSizes(GridReflowState&   aState,
   aState.mRows.ResolveIntrinsicSize(aState, mGridItems, rowFunctions,
                                     &GridArea::mRows, rowPercentageBasis,
                                     aConstraint);
+  if (aConstraint != nsLayoutUtils::MIN_ISIZE) {
+    aState.mRows.DistributeFreeSpace(aContentBox.BSize(wm));
+  }
 }
 
 bool

layout/reftests/css-grid/grid-whitespace-handling-2-ref.xhtml

@@ -14,7 +14,7 @@
     <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com"/>
     <link rel="stylesheet" type="text/css" href="support/ahem.css" />
     <style>
-      div { height: 100px; }
+      div.a, div.b, div.grid { height: 100px; }
       div.grid {
         white-space: pre;
         border: 1px dashed blue;