XNA 4.0 Spritbatch -渲染目标不能在设备上设置

Question

我正在将XNA 3.0的云效果转换为XNA 4.0，但我得到一个错误

"The render target must not be set on the device when it is used as a texture."

发生在本行的第二个循环中:

mover.Parameters["PressureMap"].SetValue(PressureOffsets);

代码:

for (int i = 0; i < 10; i++)
{
   graf.SetRenderTarget(rt5);
   mover.Parameters["PressureMap"].SetValue(PressureOffsets);
   mover.Parameters["DivergenceMap"].SetValue(Divergence);
   mover.CurrentTechnique = mover.Techniques["Jacobi"];
   mover.CurrentTechnique.Passes[0].Apply();
   sp.Begin(SpriteSortMode.Deferred, BlendState.Opaque, SamplerState.PointWrap, DepthStencilState.DepthRead, RasterizerState.CullNone);
   sp.Draw(Velocity, new Vector2(0, 0), Color.White);
   sp.End();
   graf.SetRenderTarget(null);
   PressureOffsets = rt5;
}

似乎我不能在XNA 4.0中设置纹理作为效果参数，如果它已经设置为rendertarget。但我不知道如何将其转换为XNA 4.0中的工作:(

Answer 1

我解决了。有必要用一个新的渲染目标来改变渲染目标。我使用了一个辅助类"RenderTargetState"。

    public RenderTargetState SetToDevice()
    {
        oldState = new RenderTargetState(GraphicsDevice);
        GraphicsDevice.SetRenderTarget(new RenderTarget2D(GraphicsDevice, renderTargetWidth, renderTargetHeight));
        return oldState;
    }
    public RenderTargetState BeginRenderToTexture()
    {
        oldState = SetToDevice();
        return oldState;
    }
    public Texture2D EndRenderGetTexture()
    {
        RenderTargetState renderBuffer = oldState.SetToDevice();
        oldState = null;
        return renderBuffer.RenderTarget;
    }

代码现在是这样的:

for (int i = 0; i < 10; i++)
{
  rt5.BeginRenderToTexture();
  graf.SetRenderTarget(rt5.RenderTarget);    
  mover.Parameters["PressureMap"].SetValue(PressureOffsets);
  mover.Parameters["DivergenceMap"].SetValue(Divergence);
  mover.CurrentTechnique = mover.Techniques["Jacobi"];
  mover.CurrentTechnique.Passes[0].Apply();
  sp.Begin(SpriteSortMode.Deferred, BlendState.Opaque);
  sp.Draw(Velocity, new Vector2(0, 0), Color.White);
  sp.End();
  graf.SetRenderTarget(null);
  PressureOffsets = rt5.EndRenderGetTexture();
}

Answer 2

有一个更简单的方法。

rt5 = PressureOffsets as RenderTarget2D
graf.SetRenderTarget(null);
PressureOffsets = rt5;