On 23-06-11 14:28, Krzysztof Kosiński wrote:
W dniu 23 czerwca 2011 14:10 użytkownik Chris Morgan <chris.morganiser@...400...> napisał:
It is even as I feared and expected. This Cairo renderer breaks filters which use the BackgroundImage source even more than they were already
I didn't put much effort into implementing correct BackgroundImage handling yet. The semantics of BackgroundImage make absolutely no sense for meat the moment. For example, background accumulation has to be explicitly enabled (there seems to be no UI for setting this besides the XML editor), and objects are rendered onto the background without filters. I got it only to the point where blend modes and other per-pixel filters worked correctly.
I was going to write: "As far as I can tell objects on the background image should be filtered. The spec does say something about filters and masking and such, but this just means ..." But I must confess that the explanation is a bit fuzzy to say the least, I'll ask for clarification on the svg mailing list.
As for enable-background, I think the main use case is that by explicitly setting it on an element you can avoid also taking its background into account. I can imagine this might be useful, especially when you want to make a kind of "reusable" element. That it is not enabled by default on the root element is probably to make sure that mobile applications and such don't need to invest in extra bookkeeping when it's not necessary.
I can also say that "average quality" rendering of Gaussian blurs with high levels of blur looks far worse than it used to (though it's definitely faster).
I would be interested in getting a screenshot comparison. It might be related to the fact that Cairo does not properly downscale images at the moment (no supersampling).
Is this just a flag or a limitation of Cairo?