WPF is Microsoft’s new API for graphics and user interface work. Its object-oriented all the way down, is architected to efficiently work across remote desktop, and is to a certain extent hardware accelerated.
To the developer, the API appears as a “scene graph” or strongly typed DOM tree called the “Visual Tree”, and changing what is displayed on screen is effected by making changes to the “Visual Tree”.
Theres really two parts to this API, one of which is hidden from the user. Manipulations to the “Visual Tree” are asynchronously sent across to the hidden API as deltas. Presumably, the hidden API maintains a copy of the “Visual Tree”, which it then uses for rendering. The advantage of this approach is in enabling remote-desktop capabilities. The “Visual Tree” can exists on one machine, while the rendering of that tree can happen on another computer, the deltas being sent across the net.
When writing high-performance code for WPF, its important to recognise that this asynchronous communications channel exists, and comes with a price. Optimisation now spans not only considerations of what is being displayed, but also the volume of changes being made to the Visual Tree (and therefore the aggregate quantity, size, and complexity of the deltas being sent across to the hidden API).
A prime example of the impact of this architecture is animation. In WPF, a number of animation classes are provided, for example, for animating an object along a path. Using these animation classes is a huge win, because the parameters for the path are fairly compact and need only be sent across to the hidden API once (and there are possibly other rendering optimisations the hidden API can make by knowing the animation path ahead of time). If you attempt to animate an object along a path by sending it new coordinates N times per second, performance suffers.
Another example of the impact of this communications channel is that it is often more efficient to make one large change to the visual tree rather than many small changes. In practice, this will entail taking a clone of a subtree, making the required changes, and then swapping this modified subtree into place. This last technique is a very important one to be aware of.
Whilst what I know about this communications channel is limited mostly to educated guesswork, I would say that there is some kind of serialization involved, with the tree deltas being serialized to something like BAML (a Binary-XML-like serialization format) before being sent across the wire. Even when the visual tree and the renderer exist on the same machine, the communications channel still exists and is relatively expensive. It is quite possible to saturate the channel (i.e. go to 100% CPU usage), by trying to push too many deltas through it.
Optimisation for WPF is in some ways a data compression problem. If you can get your data “over to the other side” once, and then send compact control parameters over to manipulate or select that data, you get a net win. For rich-media applications, this stuff isn’t too much of a problem, but for applications with volumes of unanticipated data, such as real-time visualisations, grids of ticking stock data, and so forth, its a bit of a problem.
What would be interesting is if the communications channel was in some way programmable, such that the programmer could push code over the channel “to the other side”, and then push a stream of data to be interpreted by that code.
Again, my understanding of this communications channel comes mostly from seeing the shadows it casts, rather than having dragged the beast out into the harsh light of day and beating the life out of it. If anyone can correct me on anything I have said, or help me understand this better, I would greatly appreciate it.america first creditalmondnet adverse credit remortgage httpprograms accredited nurse anethesiaaccreditation abft costunion abnb creditaccreditation ct acr phantomcredit card processingcom merchant washington accountcredit union alcona alpena Map