XNA to render 3D video (fixed FPS!)

i have to develop an application in wich the final step is to export a video (or a single frame) of a 3D animation generated by my software calculating the user input parameters.

I want to use XNA and for this. i need that the software can export FIXED FPS video (or also all single frames of the video separately). It's not a matter the LIVE FPS. I don't need to view on the screen the frames at a fixed fps. As the animation could be very complex, i could accept if the software take 1 minute for each frame.

The important is that i can see the frame while it render and that is not skipped any frame. eg. if the video is 1 minute long, it have to export 24 frames at 24fps also if it will take 20secs to render each frame.开发者_运维知识库 After rendered the first frame (so after 20sec) it haven't to render the frame at 21sec. it have to render the frame [2/24 of the first minute]

How can i obtain this?

Thanks!

Here is the method for doing this for XNA 4.0, described in code for your Game class (because it's easy for me):

protected override void Update(GameTime gameTime)
{
    // Do Nothing!
}

void RealUpdate()
{
    const float deltaTime = 1f/60f; // Fixed 60 FPS     
    // Update your scene here
}

RenderTarget2D screenshot;

protected override void LoadContent()
{
    screenshot = new RenderTarget2D(GraphicsDevice, width, height, false, SurfaceFormat.Color, null);
}

protected override void UnloadContent()
{
    screenshot.Dispose();
}

int i = 0;

protected override void Draw(GameTime)
{
    RealUpdate(); // Do the update once before drawing each frame.

    GraphicsDevice.SetRenderTarget(screenshot); // rendering to the render target
    //
    // Render your scene here
    //
    GraphicsDevice.SetRenderTarget(null); // finished with render target

    using(FileStream fs = new FileStream(@"screenshot"+(i++)+@".png", FileMode.OpenOrCreate)
    {
        screenshot.SaveAsPng(fs, width, height); // save render target to disk
    }

    // Optionally you could render your render target to the screen as well so you can see the result!

    if(done)
        Exit();
}

Note: I wrote this without compiling or testing - so there might be a minor error or two.