Fix matrix3d transform under page zoom

third_party/WebKit/Source/core/css/resolver/TransformBuilder.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 278 matching lines @@
             toCSSPrimitiveValue(transformValue->item(5)).getDoubleValue();
         operations.operations().append(
             MatrixTransformOperation::create(a, b, c, d, e, f));
         break;
       }
       case TransformOperation::Matrix3D: {
         TransformationMatrix matrix(
             toCSSPrimitiveValue(transformValue->item(0)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(1)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(2)).getDoubleValue(),
-            toCSSPrimitiveValue(transformValue->item(3)).getDoubleValue(),
+            toCSSPrimitiveValue(transformValue->item(3)).getDoubleValue() /
+                zoomFactor,
             toCSSPrimitiveValue(transformValue->item(4)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(5)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(6)).getDoubleValue(),
-            toCSSPrimitiveValue(transformValue->item(7)).getDoubleValue(),
+            toCSSPrimitiveValue(transformValue->item(7)).getDoubleValue() /
+                zoomFactor,
             toCSSPrimitiveValue(transformValue->item(8)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(9)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(10)).getDoubleValue(),
-            toCSSPrimitiveValue(transformValue->item(11)).getDoubleValue(),
+            toCSSPrimitiveValue(transformValue->item(11)).getDoubleValue() /
+                zoomFactor,
             zoomFactor *
                 toCSSPrimitiveValue(transformValue->item(12)).getDoubleValue(),
             zoomFactor *
                 toCSSPrimitiveValue(transformValue->item(13)).getDoubleValue(),
-            toCSSPrimitiveValue(transformValue->item(14)).getDoubleValue(),
+            zoomFactor *

[pdr., 2016/11/08 07:04:08]

WDYT of extracting this out of the loop and only applying it at the end?

Something like:
for (auto& value : toCSSValueList(inValue)) {
   ... (case stmts)
}

float zoomFactor = conversionData.zoom();
if (zoomFactor != 1)
    operations = operations.zoom(zoomFactor);
return operations;

[Franklin Ta, 2016/11/08 07:52:18]

You also have to refactor the zoom adjustment in the other cases(perspective and
translate) if you want to move all of that logic into operations.zoom so it
might end up being a messier change. For example in the perspective case I think
I might need to unzoom the value from computeLength just so it can be zoomed
again later.

Can I leave this for someone a bit more experienced with the code base? I was
hoping this CL can just be for correctness and alancutter can do the refactor
(or assign it to someone) since he added the zoom method in operations.

[Franklin Ta, 2016/11/08 16:47:02]

Btw @alancutter if you're not the owner for this, don't worry about it. I was
assuming that you dealt with the same problem elsewhere when you added that zoom
method so you would know how to best refactor this. I just took another look at
where TransformOperations::zoom is used inside AnimationStyleBuilder and it
doesn't look like it uses similar code for handling zoom at all.

The main complexity here is in the perspective and translate cases where you
need to calculate them using unzoomed lengths. The call hierarchy for
convertToFloatLength is pretty deep (to me) to figure out when exactly
zoomFactor got multiplied in to see how to remove it.

For example: it goes convertToFloatLength -> convertToLength -> computeLength ->
computeLengthDouble -> zoomedComputedPixels but not when it's
em/rem/percentage/calc/etc. I think it might just a multiply by the zoomFactor
at some point for all cases so you can just divide the existing code by the
zoomFactor to undo the zoom but this has to be verified and tested.

Anyway, if there's a refactor necessary here I might not be the best person to
help out with this. =(

+                toCSSPrimitiveValue(transformValue->item(14)).getDoubleValue(),
             toCSSPrimitiveValue(transformValue->item(15)).getDoubleValue());
         operations.operations().append(
             Matrix3DTransformOperation::create(matrix));
         break;
       }
       case TransformOperation::Perspective: {
         double p = firstValue.computeLength<double>(conversionData);
         ASSERT(p >= 0);
         operations.operations().append(
             PerspectiveTransformOperation::create(p));
         break;
       }
       default:
         ASSERT_NOT_REACHED();
         break;
     }
   }
   return operations;
 }
 
 }  // namespace blink