Don't paint a border after the last frame on any axis in a frameset

Source/core/paint/FrameSetPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/FrameSetPainter.h"
 
 #include "core/html/HTMLFrameSetElement.h"
 #include "core/layout/LayoutFrameSet.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
@@ skipping 44 matching lines @@
     context->fillRect(borderRect, m_layoutFrameSet.frameSet()->hasBorderColor() ? m_layoutFrameSet.resolveColor(CSSPropertyBorderLeftColor) : borderFillColor());
 
     // Now stroke the edges but only if we have enough room to paint both edges with a little
     // bit of the fill color showing through.
     if (borderRect.height() >= 3) {
         context->fillRect(IntRect(borderRect.location(), IntSize(m_layoutFrameSet.size().width(), 1)), borderStartEdgeColor());
         context->fillRect(IntRect(IntPoint(borderRect.x(), borderRect.maxY() - 1), IntSize(m_layoutFrameSet.size().width(), 1)), borderEndEdgeColor());
     }
 }
 
+static bool shouldPaintBorderAfter(const LayoutFrameSet::GridAxis& axis, size_t index)
+{
+    // Should not paint a border after the last frame along the axis.
+    return index + 1 < axis.m_sizes.size() && axis.m_allowBorder[index + 1];

[chrishtr, 2015/06/05 18:57:27]

Why index + 1 < axis.m_sizes.size() and not index < .m_sizes.size() ?

[fs, 2015/06/05 19:18:46]

index is in [0, size()-1], so the latter will always be true. Essentially reject
the last index. An equivalent expression would be:

index < axis.m_sizes.size() - 1 (or even "index != axis.m_sizes.size() - 1" if
one allows oneself)

Maybe that is more clear? (Didn't fancy the subtraction very much myself.)

+}
+
 void FrameSetPainter::paintBorders(const PaintInfo& paintInfo, const LayoutPoint& adjustedPaintOffset)
 {
     LayoutRect adjustedFrameRect(adjustedPaintOffset, m_layoutFrameSet.size());
     LayoutObjectDrawingRecorder recorder(*paintInfo.context, m_layoutFrameSet, paintInfo.phase, adjustedFrameRect);
     if (recorder.canUseCachedDrawing())
         return;
 
+    LayoutUnit borderThickness = m_layoutFrameSet.frameSet()->border();
+    if (!borderThickness)
+        return;
+
     LayoutObject* child = m_layoutFrameSet.firstChild();
     size_t rows = m_layoutFrameSet.rows().m_sizes.size();
     size_t cols = m_layoutFrameSet.columns().m_sizes.size();
-    LayoutUnit borderThickness = m_layoutFrameSet.frameSet()->border();
     LayoutUnit yPos = 0;
     for (size_t r = 0; r < rows; r++) {
         LayoutUnit xPos = 0;
         for (size_t c = 0; c < cols; c++) {
             xPos += m_layoutFrameSet.columns().m_sizes[c];
-            if (borderThickness && m_layoutFrameSet.columns().m_allowBorder[c + 1]) {
+            if (shouldPaintBorderAfter(m_layoutFrameSet.columns(), c)) {
                 paintColumnBorder(paintInfo, pixelSnappedIntRect(
                     LayoutRect(adjustedPaintOffset.x() + xPos, adjustedPaintOffset.y() + yPos, borderThickness, m_layoutFrameSet.size().height())));
                 xPos += borderThickness;
             }
             child = child->nextSibling();
             if (!child)
                 return;
         }
         yPos += m_layoutFrameSet.rows().m_sizes[r];
-        if (borderThickness && m_layoutFrameSet.rows().m_allowBorder[r + 1]) {
+        if (shouldPaintBorderAfter(m_layoutFrameSet.rows(), r)) {
             paintRowBorder(paintInfo, pixelSnappedIntRect(
                 LayoutRect(adjustedPaintOffset.x(), adjustedPaintOffset.y() + yPos, m_layoutFrameSet.size().width(), borderThickness)));
             yPos += borderThickness;
         }
     }
 }
 
 void FrameSetPainter::paintChildren(const PaintInfo& paintInfo, const LayoutPoint& adjustedPaintOffset)
 {
     // Paint only those children that fit in the grid.
@@ skipping 20 matching lines @@
     LayoutObject* child = m_layoutFrameSet.firstChild();
     if (!child)
         return;
 
     LayoutPoint adjustedPaintOffset = paintOffset + m_layoutFrameSet.location();
     paintChildren(paintInfo, adjustedPaintOffset);
     paintBorders(paintInfo, adjustedPaintOffset);
 }
 
 } // namespace blink