Implement support for the 'transform-box' property

third_party/WebKit/Source/core/svg/SVGElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Nikolas Zimmermann
  * <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Alp Toker <alp@atoker.com>
  * Copyright (C) 2009 Cameron McCormack <cam@mcc.id.au>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 298 matching lines @@
     return true;
   if (style.transform().dependsOnBoxSize())
     return true;
   if (style.translate() && style.translate()->dependsOnBoxSize())
     return true;
   if (style.hasOffset())
     return true;
   return false;
 }
 
+static FloatRect computeTransformReferenceBox(const SVGElement& element) {
+  const LayoutObject& layoutObject = *element.layoutObject();
+  const ComputedStyle& style = layoutObject.styleRef();
+  if (!RuntimeEnabledFeatures::cssTransformBoxEnabled()) {
+    FloatRect referenceBox = layoutObject.objectBoundingBox();
+    // Set the reference origin to zero when transform-origin (x/y) has a
+    // non-percentage unit.
+    const TransformOrigin& transformOrigin = style.transformOrigin();
+    if (transformOrigin.x().type() != Percent)
+      referenceBox.setX(0);
+    if (transformOrigin.y().type() != Percent)
+      referenceBox.setY(0);
+    return referenceBox;
+  }
+  if (style.transformBox() == ETransformBox::kFillBox)

[pdr., 2017/04/04 22:47:13]

I was looking at Gecko's implementation and they also just have two cases:
fill-box and not-fill-box:
https://bug923193.bmoattachments.org/attachment.cgi?id=8607931. Do you know why
the spec has both kBorderBox and kViewBox?

[fs, 2017/04/05 08:48:17]

I've not managed to find any relevant minutes about this ([1] hints there was
discussion), so I can only guess. Maybe because 'border-box' is a weird
(non-obvious) value for what it does (for SVG), so the "alias" 'view-box' is
better suited?

[1] https://lists.w3.org/Archives/Public/www-style/2014Nov/0000.html

+    return layoutObject.objectBoundingBox();
+  DCHECK(style.transformBox() == ETransformBox::kBorderBox ||
+         style.transformBox() == ETransformBox::kViewBox);
+  SVGLengthContext lengthContext(&element);
+  FloatSize viewportSize;
+  lengthContext.determineViewport(viewportSize);
+  return FloatRect(FloatPoint(), viewportSize);
+}
+
 AffineTransform SVGElement::calculateTransform(
     ApplyMotionTransform applyMotionTransform) const {
   const ComputedStyle* style =
       layoutObject() ? layoutObject()->style() : nullptr;
 
   // If CSS property was set, use that, otherwise fallback to attribute (if
   // set).
   AffineTransform matrix;
   if (style && style->hasTransform()) {
-    TransformationMatrix transform;
-    float zoom = style->effectiveZoom();
-
-    FloatRect boundingBox = layoutObject()->objectBoundingBox();
+    FloatRect referenceBox = computeTransformReferenceBox(*this);
     ComputedStyle::ApplyTransformOrigin applyTransformOrigin =
         ComputedStyle::IncludeTransformOrigin;
     // SVGTextElements need special handling for the text positioning code.
     if (isSVGTextElement(this)) {
       // Do not take into account transform-origin, or percentage values.
-      boundingBox = FloatRect();
+      referenceBox = FloatRect();
       applyTransformOrigin = ComputedStyle::ExcludeTransformOrigin;
     }
 
     if (transformUsesBoxSize(*style, applyTransformOrigin))
       UseCounter::count(document(), UseCounter::TransformUsesBoxSizeOnSVG);
 
     // CSS transforms operate with pre-scaled lengths. To make this work with
     // SVG (which applies the zoom factor globally, at the root level) we
     //
-    //   * pre-scale the bounding box (to bring it into the same space as the
+    //   * pre-scale the reference box (to bring it into the same space as the
     //     other CSS values)
     //   * invert the zoom factor (to effectively compute the CSS transform
     //     under a 1.0 zoom)
     //
     // Note: objectBoundingBox is an emptyRect for elements like pattern or
     // clipPath. See the "Object bounding box units" section of
     // http://dev.w3.org/csswg/css3-transforms/
+    float zoom = style->effectiveZoom();
+    TransformationMatrix transform;
     if (zoom != 1) {
-      boundingBox.scale(zoom);
+      referenceBox.scale(zoom);
       transform.scale(1 / zoom);
       style->applyTransform(
-          transform, boundingBox, applyTransformOrigin,
+          transform, referenceBox, applyTransformOrigin,
           ComputedStyle::IncludeMotionPath,
           ComputedStyle::IncludeIndependentTransformProperties);
       transform.scale(zoom);
     } else {
       style->applyTransform(
-          transform, boundingBox, applyTransformOrigin,
+          transform, referenceBox, applyTransformOrigin,
           ComputedStyle::IncludeMotionPath,
           ComputedStyle::IncludeIndependentTransformProperties);
     }
     // Flatten any 3D transform.
     matrix = transform.toAffineTransform();
   }
 
   // Apply any "motion transform" contribution if requested (and existing.)
   if (applyMotionTransform == IncludeMotionTransform && hasSVGRareData())
     matrix.preMultiply(*svgRareData()->animateMotionTransform());
@@ skipping 924 matching lines @@
   visitor->trace(m_className);
   Element::trace(visitor);
 }
 
 const AtomicString& SVGElement::eventParameterName() {
   DEFINE_STATIC_LOCAL(const AtomicString, evtString, ("evt"));
   return evtString;
 }
 
 }  // namespace blink