Support subpixel values for text-shadow and box-shadow

Source/core/rendering/RenderBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 2464 matching lines @@
     bool hasOpaqueBackground = s->visitedDependentColor(CSSPropertyBackgroundColor).isValid() && s->visitedDependentColor(CSSPropertyBackgroundColor).alpha() == 255;
 
     GraphicsContextStateSaver stateSaver(*context, false);
 
     const ShadowList* shadowList = s->boxShadow();
     for (size_t i = shadowList->shadows().size(); i--; ) {
         const ShadowData& shadow = shadowList->shadows()[i];
         if (shadow.style() != shadowStyle)
             continue;
 
-        IntSize shadowOffset(shadow.x(), shadow.y());
-        int shadowBlur = shadow.blur();
-        int shadowSpread = shadow.spread();
+        LayoutSize shadowOffset(shadow.x(), shadow.y());
+        LayoutUnit shadowBlur = shadow.blur();
+        LayoutUnit shadowSpread = shadow.spread();
 
         if (shadowOffset.isZero() && !shadowBlur && !shadowSpread)
             continue;
 
         const Color& shadowColor = resolveColor(shadow.color());
 
         if (shadow.style() == Normal) {
-            RoundedRect fillRect = border;
+            FloatRect fillRect = border.rect();
             fillRect.inflate(shadowSpread);
             if (fillRect.isEmpty())
                 continue;
 
-            IntRect shadowRect(border.rect());
+            LayoutRect shadowRect(border.rect());
             shadowRect.inflate(shadowBlur + shadowSpread);
             shadowRect.move(shadowOffset);
 
             // Save the state and clip, if not already done.
             // The clip does not depend on any shadow-specific properties.
             if (!stateSaver.saved()) {
                 stateSaver.save();
                 if (hasBorderRadius) {
                     RoundedRect rectToClipOut = border;
 
                     // If the box is opaque, it is unnecessary to clip it out. However, doing so saves time
                     // when painting the shadow. On the other hand, it introduces subpixel gaps along the
                     // corners. Those are avoided by insetting the clipping path by one pixel.
                     if (hasOpaqueBackground)
                         rectToClipOut.inflateWithRadii(-1);
 
                     if (!rectToClipOut.isEmpty()) {
                         context->clipOutRoundedRect(rectToClipOut);
                     }
                 } else {
+                    // This IntRect is correct even with fractional shadows, because it is used for the rectangle
+                    // of the box itself, which is always pixel-aligned.
                     IntRect rectToClipOut = border.rect();
 
                     // If the box is opaque, it is unnecessary to clip it out. However, doing so saves time
                     // when painting the shadow. On the other hand, it introduces subpixel gaps along the
                     // edges if they are not pixel-aligned. Those are avoided by insetting the clipping path
                     // by one pixel.
                     if (hasOpaqueBackground) {
                         // FIXME: The function to decide on the policy based on the transform should be a named function.
                         // FIXME: It's not clear if this check is right. What about integral scale factors?
                         AffineTransform transform = context->getCTM();
                         if (transform.a() != 1 || (transform.d() != 1 && transform.d() != -1) || transform.b() || transform.c())
                             rectToClipOut.inflate(-1);
                     }
 
                     if (!rectToClipOut.isEmpty()) {
                         context->clipOut(rectToClipOut);
                     }
                 }
             }
 
             // Draw only the shadow.
             DrawLooper drawLooper;
             drawLooper.addShadow(shadowOffset, shadowBlur, shadowColor,
                 DrawLooper::ShadowRespectsTransforms, DrawLooper::ShadowIgnoresAlpha);
             context->setDrawLooper(drawLooper);
 
             if (hasBorderRadius) {
-                RoundedRect influenceRect(shadowRect, border.radii());
+                // XXX is this IntRect conversion correct?

[eae, 2013/11/27 23:45:27]

Why not use pixelSnappedIntRect instead?

[cbiesinger, 2013/12/18 02:09:12]

Good idea, thanks.

+                RoundedRect influenceRect(IntRect(shadowRect.pixelSnappedLocation(), shadowRect.pixelSnappedSize()), border.radii());
                 influenceRect.expandRadii(2 * shadowBlur + shadowSpread);
                 if (allCornersClippedOut(influenceRect, info.rect))
-                    context->fillRect(fillRect.rect(), Color::black);
+                    context->fillRect(fillRect, Color::black);
                 else {
-                    fillRect.expandRadii(shadowSpread);
-                    if (!fillRect.isRenderable())
-                        fillRect.adjustRadii();
-                    context->fillRoundedRect(fillRect, Color::black);
+                    RoundedRect roundedFillRect = border;
+                    roundedFillRect.inflate(shadowSpread);
+
+                    roundedFillRect.expandRadii(shadowSpread);
+                    if (!roundedFillRect.isRenderable())
+                        roundedFillRect.adjustRadii();
+                    context->fillRoundedRect(roundedFillRect, Color::black);
                 }
             } else {
-                context->fillRect(fillRect.rect(), Color::black);
+                context->fillRect(fillRect, Color::black);
             }
         } else {
+            // inset shadow

[eae, 2013/11/27 23:45:27]

Update comment to be more descriptive or remove it.

[cbiesinger, 2013/12/18 02:09:12]

Done.

             GraphicsContext::Edges clippedEdges = GraphicsContext::NoEdge;
             if (!includeLogicalLeftEdge) {
                 if (isHorizontal)
                     clippedEdges |= GraphicsContext::LeftEdge;
                 else
                     clippedEdges |= GraphicsContext::TopEdge;
             }
             if (!includeLogicalRightEdge) {
                 if (isHorizontal)
                     clippedEdges |= GraphicsContext::RightEdge;
                 else
                     clippedEdges |= GraphicsContext::BottomEdge;
             }
-            context->drawInnerShadow(border, shadowColor, shadowOffset, shadowBlur, shadowSpread, clippedEdges);
+            // TODO: support non-integer shadows
+            context->drawInnerShadow(border, shadowColor, IntSize(shadowOffset.width(), shadowOffset.height()), shadowBlur, shadowSpread, clippedEdges);

[eae, 2013/11/27 23:45:27]

do you want to floor or round the offset here? Use flooredIntSize or
roundedIntSize to be explicit.

[cbiesinger, 2013/12/18 02:09:12]

Ah, thanks - done. Switched to floored because that's what we used to do.

         }
     }
 }
 
 LayoutUnit RenderBoxModelObject::containingBlockLogicalWidthForContent() const
 {
     return containingBlock()->availableLogicalWidth();
 }
 
 RenderBoxModelObject* RenderBoxModelObject::continuation() const
@@ skipping 227 matching lines @@
     ASSERT(!beforeChild || toBoxModelObject == beforeChild->parent());
     for (RenderObject* child = startChild; child && child != endChild; ) {
         // Save our next sibling as moveChildTo will clear it.
         RenderObject* nextSibling = child->nextSibling();
         moveChildTo(toBoxModelObject, child, beforeChild, fullRemoveInsert);
         child = nextSibling;
     }
 }
 
 } // namespace WebCore