CSS Properties and Values API: Implement computation / computational independence

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

Index: third_party/WebKit/Source/core/css/resolver/StyleBuilderConverter.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleBuilderConverter.cpp b/third_party/WebKit/Source/core/css/resolver/StyleBuilderConverter.cpp
index 1bc0a649f87fa512c378d544cfd6871b4eb3d722..a3156a8baf3764c0670be10540ace3ac32d1a1b2 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleBuilderConverter.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleBuilderConverter.cpp
@@ -1103,7 +1103,21 @@ PassRefPtr<StylePath> StyleBuilderConverter::convertPathOrNone(StyleResolverStat
 
 const CSSValue& StyleBuilderConverter::convertRegisteredPropertyValue(const StyleResolverState& state, const CSSValue& value)
 {
-    // TODO(timloh): Resolve ems, etc.
+    // TODO(timloh): Images and transform-function values can also contain lengths.
+    if (value.isValueList()) {
+        CSSValueList* newList = CSSValueList::createSpaceSeparated();
+        for (const CSSValue* innerValue : toCSSValueList(value))
+            newList->append(convertRegisteredPropertyValue(state, *innerValue));
+        return *newList;
+    }
+
+    if (value.isPrimitiveValue()) {
+        const CSSPrimitiveValue& primitiveValue = toCSSPrimitiveValue(value);
+        if (primitiveValue.isCalculated() || CSSPrimitiveValue::isRelativeUnit(primitiveValue.typeWithCalcResolved())) {
+            Length length = primitiveValue.convertToLength(state.cssToLengthConversionData().copyWithAdjustedZoom(1));

[sashab, 2016/09/22 00:29:22]

I think we should really use the actual zoom here. If a user zooms in the page
their custom properties should change values, otherwise we'll get
inconsistencies and bugs.

Alternatively you could add a comment like:
// To not have any chance of values changing slightly due to rounding at
different zoom levels, ignore the zoom here.
But that just sounds like it's incorrect behavior, doesn't it?

[Timothy Loh, 2016/09/22 02:42:48]

I'm not sure what you're getting at here. If I specify left: 10px, I don't
expect it to end up as 20px. Similarly, if I specify --left: 10px, I also don't
expect it to end up as 20px.

[sashab, 2016/09/22 06:02:35]

Ok, add this comment then :)

[alancutter (OOO until 2018), 2016/09/22 07:58:41]

Agreed, at the very least add the comment.
I think any rounding errors here would be too negligible to worry about though.

[Timothy Loh, 2016/09/22 08:18:58]

Comment added. Probably negligible, but I prefer it this way. Since typed om
will return lengths as floats and not 6sf strings, maybe it matters more... I
dunno :/

+            return *CSSPrimitiveValue::create(length, 1);
+        }
+    }
     return value;
 }