2

I'm working on a real-time WPF/Silverlight (and soon WP7) visualization component and I'm looking for the best solution to force a redraw of the entire component in a Game-loop style. Redraw should be on-demand, but I don't want to back up the message pump with re-draw calls. Most of the drawing in my component is done using non-WPF primitives (e.g. Bitmap Interop, Direct2D) so my code does not use InvalidateVisual, and as a result, currently looks like this

// Pseudocode, doesnt compile, just to convey the meaning
public void InvalidateElement()
{
    if (CurrentlyDrawing)
        return;

    Dispatcher.BeginInvoke(() => 
    {
        CurrentlyDrawing = true;

        DoDrawInternal();

        CurrentlyDrawing = false;            
    }
}

Ok so this is great. If I call InvalidateElement lots of times I get good responsiveness. However, what I want to do is ensure I can push data to my visualization component as fast as possible but only draw when the component is able to draw, and not keep drawing to catch up with the data once the input stream completes.

No I can't override OnRender, I'm using non-WPF drawing inside WPF ;-)

Basically what I want is something like the old Invalidate() / OnPaint in WindowsForms, or better yet, a game loop in DirectX.

At the moment I get the situation where if I have an external thread that pushes data to the visualization component at a high rate then if I Stop pushing data I get another 20 seconds worth of refreshes to get through before the component stops drawing. I want to stop drawing as soon as data has gone in.

Another idea I had was to handle CompositionTarget.Rendering in the visualization component then implement some sort of rudimentary Queue to push data to and the Rendering event consumes this data as fast as it can.

In Summary

Given a WPF visualization component, V, and a datasource which pushes it data every 1ms, D, how can I ensure that no matter the datarate of D, V draws data at 30FPS (or whatever it can do) and updates itself in chunks, sort of how a game render loop does in DirectX?

When the data stops, V should redraw everything it has up to now in one go. When the data is too fast, V draws larger chunks at a time to compensate.

If you need more information I'd be happy to share it. Right now I've just posted a synopsis to gauge if there are any quick fixes but a fuller Q with code examples can be provided on request.

Best regards,

4

5 回答 5

3

您可能需要考虑在 CompositionTarget.Rendering 事件上进行渲染并限制无效状态。

Silverlight 游戏循环示例 (F#)：

/// Run game
let runGame () =
    let state = gameState.GetEnumerator()
    let rate = TimeSpan.FromSeconds(1.0/50.0)
    let lastUpdate = ref DateTime.Now
    let residual = ref (TimeSpan())
    CompositionTarget.Rendering.Add (fun x -> 
        let now = DateTime.Now
        residual := !residual + (now - !lastUpdate)
        while !residual > rate do
            state.MoveNext() |> ignore
            residual := !residual - rate
        lastUpdate := now
    )

玩游戏：http ://trelford.com/blog/post/LightCycles.aspx

阅读来源：https ://bitbucket.org/ptrelford/lightcycles

于 2012-01-06T08:07:28.993 回答
1

您是否想过使用以 30FPS 运行的调度计时器，然后对当前数据进行快照并在每个计时器滴答时渲染它？如果您想在没有任何更改的情况下避免重绘，您可以简单地保留 LastChanged 和 LastRendered 的时间戳，仅在 LastChanged > LastRendered 时执行实际重绘。基本上更新数据和渲染数据是相互分离的；主要技巧是确保您可以在渲染线程想要渲染数据时以某种方式获得数据的连贯快照（即您需要某种锁定。）

于 2012-01-05T23:44:41.387 回答
1

我最近正在处理一个需要类似游戏循环风格的项目。尽管我的示例纯粹是在 F# 中，但您也可以弄清楚如何在 C# 中这样做，可能是使用一些互操作代码来初始化计时器并连接事件，如下面的链接中给出的，

http://dl.dropbox.com/u/23500975/Demos/loopstate.zip

该示例没有显示如何重绘，它只是每 500 毫秒更新一次基础股票数据，它应该适用于任何类型的 WPF 绘图机制。核心思想是使用可组合事件，在 F# 中，一个事件是一等公民 + 一个 IObservable（C# 的响应式扩展），因此我们可以轻松组合返回一组事件或单个事件的函数。有一个函数 Observable.await，它接受一个 Observable 并返回一个状态。

            eventSource
            |> Observable.await(fun (t:State.t) e ->
                // return the modified state back on every check or in the end
                match e with
                // start button click
                | Choice1Of3(_) ->
                    {t with start=true}

                // stop button click
                | Choice2Of3(_) ->
                    {t with start=false}

                // timer tick event,
                | Choice3Of3(_) ->
                    if t.start = true then
                        handleStockUpdate(t)
                    else t
            ) (state)

我只是在这里使用了一些 FP 术语，但它应该可以正常使用这里的正常 C# (OO) 做事方式。

希望这可以帮助！

-法赫德

于 2012-01-06T12:56:09.883 回答
1

您可以收听CompositionTarget.Rendering在 WPF 呈现 UI 之前触发的事件，并在其中进行绘图。

另一个花絮.. InvalidateVisuals() 与 Form.Invalidate() 完全不同，因为它还会导致代价高昂的重新布局。如果您想要 Form.Invalidate() 之类的东西，则创建一个 DrawingGroup（或位图图像）“backingStore”，在 OnRender() 期间将其放置在 DrawingContext 中，然后随时更新它。WPF 将自动更新和重绘 UI。

于 2017-06-08T04:21:04.260 回答
0

如果您使用非 WPF 元素进行绘图并且需要 WinForms 提供的 Invalidate() 方法，我不确定您为什么要在前端使用 WPF？你不能切换 UI 来使用 WinForms 吗？

于 2012-01-05T23:43:31.957 回答