Why is it more efficient (I know it is, given your
metrics, but want to know why)--aren't you just moving
the values already stored in the PropertyList into
separate fields in the FO objects? Yes, you're
releasing the PropertyList's memory, but the elements
that the PropertyList previously stored are now stored
in the FObj. So if PropertyList can be thought of as a C-like
struct holding the values of its FObj's properties,
what you're doing appears to be just taking that
struct's member variables and moving them to the FObj.

But, obviously, given the performance/memory boost
you're noting, PropertyList *can't* be regarded as a
C-like struct.  Why?  Could PropertyList be made more
efficient instead of this change--make it more like a
C-like struct?


It's a mixed bag, by the look of it.  From the patch, applying to FOText:

+    // The value of properties relevant for character.
+    private CommonFont commonFont;
+    private CommonHyphenation commonHyphenation;
+    private ColorType color;
+    private Property letterSpacing;
+    private SpaceProperty lineHeight;
+    private int whiteSpaceCollapse;
+    private int textTransform;
+    private Property wordSpacing;
+    private int wrapOption;
+    // End of property values

Note the combination of simple fields for whiteSpaceCollapse and more
complex structures like CommonFont.

I really like the combination of CommonXXX structures and simple fields, since it litterally matches the spec. Except that the spec doesn't have a FOText element so it is a bad example for me to use. The fields in FOText was taken from TextInfo and I suspect that eventually more fields will be needed in FOText.

In the rest of the elements, the set of fields matches the spec. The only exception is a bug where the some of the inline LayoutManagers uses "vertical-align" which is a shorthand. The layoutmanagers should instead use the properties that the shorthand sets: alignment-baseline, alignment-adjust, baseline-shift and dominant-baseline. But since only one of these properties has been implemented yet, I choose to keep the use of "vertical-align" for now.

Alt-design just uses a sparse array, constructed at END_ELEMENT.  Space
savings are progressively realized as the depth of the FO Tree reduces.
 Maximum consumption occurs at the points of greatest depth of the
tree, minima at the end of each page-sequence.

IIRC your sparse array does not just contain the relevant properties for an element (those listed in the spec under each fo:element), but the joined set of all properties relevant for all the allowed children. If this is correct, the sparse arrays stores more properties and uses more memory than my proposal does.

Finn has gone a step further, and collapsed the property structures into
local variables, which is good for both memory consumption and speed, at
the cost of some more code.  IIUC.

Correct. In addition I also get a certain level of typesafeness for the properties.


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