EM Font Size Performance

[David Grieve]

Resolving the relative size involves a lot of lookup. You have to go up 
the scene-graph from the child to find a font style. If you get to the 
root and haven't found a font style, then use the default font. 
Performance in this area could be vastly improved by passing the size 
from either a font style or the default font down the scene-graph as 
styles are evaluated. There are other style lookups that could benefit 
from this as well, resolving looked-up colors for example. I believe I 
created a bug for this a long time ago.


On 4/19/18 5:57 AM, Dean Wookey wrote:
> Hi All,
>
> In our application we add and remove a lot of nodes to the scene graph
> regularly, and also make use of em font sizes to scale certain parts of our
> application. We've noticed performance issues when adding nodes to the
> scene, and it seems to be related to em sizes in our css.
>
> As a test we added a chain of 20 stackpanes to a root stackpane. On the
> root, we set a font size of 8pt via inline css. We then added and removed a
> new tableview from the deepest stackpane 500 times, waiting for the node to
> render after each add and remove.
>
> In each of the experiments, we compared adding tableviews without css and
> adding tableviews with an inline css font size of 8pt. We then tried
> setting different font sizes in the stackpane chain.
>
> I've attached sample code for these experiments.
>
> The results (on jdk 9.0.4 - jdk 10 was similar) are as follows:
>
> Setting a 1em font size on all stackpanes except the root.
> With font on tableview: 14707ms
> Without font on tableview: 27725ms
>
> Setting a 1em font size on the first child of the root only.
> With font on tableview: 14221ms
> Without font on tableview: 19187ms
>
> Using the original setup with no additional fonts.
> With font on tableview: 13990ms
> Without font on tableview: 13847ms
>
> It looks like using a relative font size has a large effect performance
> wise on descendant nodes. I would expect some amount of font size caching
> in the chain of stackpanes since I'm reusing the same chain and
> adding/removing nodes from that chain repeatedly.
>
> I'm not sure how valid my test is, or how much of an issue this really is
> in practice?
>
> Dean