On Thu, May 2, 2013 at 12:37 AM, Benoit Jacob <jacob.benoi...@gmail.com>wrote:
> I am not very familiar with the spec. Could you please give an example of > such a filter that would absolutely require multiple passes? > Two GLSL custom filters in a chain, where each filter has its own vertex shader. If I'm not mistaken, doing those in a single pass would require inverting the function expressed by the vertex shader of the first filter, which is infeasible in general. Another example is an SVG filter where the output of one primitive is sampled by many other primitives (and not necessarily at the same pixel coordinates, when <feOffset> is involved). You could duplicate that primitive but in general that could lead to an explosion in the size of the generated program. So if such filters exist in the spec, I would argue for taking them out, at > least for now. You don't want portable-but-with-big-performance-caveats > things in a 1.0 spec. > SVG filters have already been around a long time and we can't break them at this point. The vertex shaders for custom filters are quite powerful and useful. We could prevent custom filters from being chained, but authors would just work around it by nesting elements with one custom filter each, leaving us in no better position. > I realize that we do have intermediate surfaces in our own compositor, but > at least that's (for all I know) just an implementation detail, not > something explicitly required by a spec. > It's hard to implement group opacity without them. We discussed on IRC how one could use custom shaders to eliminate intermediate surfaces, and that's a cool idea, but there are tradeoffs involved if we start generating lots of custom shaders (one per sequence of child layer types at least). Don't want to prematurely optimize. We already do simple optimizations such as a ContainerLayer with opacity and a single ThebesLayer child just pushing its opacity down to the child, avoiding an intermediate surface. So we're only talking about situations like a ContainerLayer with opacity that contains several elements with animated transforms or scrolling, or a ContainerLayer with opacity that contains Web content and a playing video. Rob -- q“qIqfq qyqoquq qlqoqvqeq qtqhqoqsqeq qwqhqoq qlqoqvqeq qyqoquq,q qwqhqaqtq qcqrqeqdqiqtq qiqsq qtqhqaqtq qtqoq qyqoquq?q qEqvqeqnq qsqiqnqnqeqrqsq qlqoqvqeq qtqhqoqsqeq qwqhqoq qlqoqvqeq qtqhqeqmq.q qAqnqdq qiqfq qyqoquq qdqoq qgqoqoqdq qtqoq qtqhqoqsqeq qwqhqoq qaqrqeq qgqoqoqdq qtqoq qyqoquq,q qwqhqaqtq qcqrqeqdqiqtq qiqsq qtqhqaqtq qtqoq qyqoquq?q qEqvqeqnq qsqiqnqnqeqrqsq qdqoq qtqhqaqtq.q" _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
