Right now, ImageLib provides very general support for multipart/x-mixed-replace images. Each part may contain a different image format (we may even switch between raster and vector images from one part to the next), individual parts may be animated, and each part may have a different size.
This has major costs for us. Supporting existing images changing their size requires that layout and content code be aware of multipart/x-mixed-replace images, and requires us to use a design that’s suboptimal for the common case of MJPEG webcam content. Because these changes in size, type, and animation state prevent many invariants we’d like to have in ImageLib from holding, we either can’t assert some things we’d like to assert, or the assertions are quite tricky to write, which leads to more bugs and more maintenance headaches. There’s also just more and uglier code to maintain: over time hacks to multipart/x-mixed-replace have popped up in many places in Gecko, inside and outside ImageLib, and I’d like to remove them. And despite all of this effort, it’s not clear to me that our support is actually very robust, because outside of our limited test suite as far as I can tell nobody uses multipart/x-mixed-replace images for anything except MJPEG! I’ve had to change how multipart/x-mixed-replace is implemented in ImageLib to support other, more important, features. As part of this refactoring, I plan to pare down our support to the minimum required for MJPEG webcams: (1) The individual parts may only be JPEG images. Other formats will not be supported. (2) All of the parts must have the same intrinsic size as the first part - in other words, size changes will not be supported. In case it’s not clear, there’ll be no effect on other uses of multipart/x-mixed-replace elsewhere in the browser. These changes are specific to images and ImageLib. Making these changes will allow me to totally encapsulate MJPEG support inside ImageLib. Other code will see an MJPEG as just another type of animated image. Virtually all of the ugly consequences of our current multipart/x-mixed-replace image support will fall away. If anyone has any concerns about this change, please let me know. We should be fairly safe in doing this since non-MJPEG multipart/x-mixed-replace images are essentially never used, and multipart/x-mixed-replace itself is not universally supported anyway - IE does not even support MJPEG, much less the more general features that we provide. There also does not seem to be any specification that requires support for multipart/x-mixed-replace images at all, although HTML5 does specify multipart/x-mixed-replace support for documents. Thanks, - Seth _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
