XNA 4.0 - 分配渲染目标时的奇怪行为答案

【问题标题】：XNA 4.0 - strange behaviour when assigning render targetXNA 4.0 - 分配渲染目标时的奇怪行为
【发布时间】：2015-01-18 23:44:56
【问题描述】：

我目前面临以下奇怪的问题：下面的代码 sn-p 按预期完美呈现：

private void DoRenderSkybox (GameTime Time) {
  this.Device.SetRenderTarget(this.GridTexture);
  this.Device.SetRenderTarget(null);


  // compute a temporary transformation matrix containing
  // the combined world and projection transfromation
  Matrix WorldViewProjection = this.Camera.View * this.Camera.Projection;

  // set the render target to the back buffer in any case
  this.Device.SetRenderTarget(null);

  // assign the vertex - declaration and the vertex- and the index - buffer
  this.Device.SetVertexBuffer(this.SkyboxVertices);
  this.Device.Indices = this.SkyboxIndices;

  // choose the appropriate technique for the current render pass
  this.SceneEffect.CurrentTechnique = SceneEffect.Techniques["Skybox"];
  this.SceneEffect.CurrentTechnique.Passes[0].Apply();
  this.SceneEffect.Parameters["WorldViewProjection"].SetValue(WorldViewProjection);

  // finally render the sykbox with disabled depth stencil buffering
  this.Device.DepthStencilState = DepthStencilState.None;
  this.Device.DrawIndexedPrimitives( PrimitiveType.TriangleList, 0, 0, 36, 0, 12);
  this.Device.DepthStencilState = DepthStencilState.Default;


  //this.Device.SetRenderTarget(this.GridTexture);
  //this.Device.SetRenderTarget(null);
}

但是，如果我在函数末尾分配（并立即取消分配）渲染目标，如下所示：

private void DoRenderSkybox (GameTime Time) {
  //this.Device.SetRenderTarget(this.GridTexture);
  //this.Device.SetRenderTarget(null);


  // compute a temporary transformation matrix containing
  // the combined world and projection transfromation
  Matrix WorldViewProjection = this.Camera.View * this.Camera.Projection;

  // set the render target to the back buffer in any case
  this.Device.SetRenderTarget(null);

  // assign the vertex - declaration and the vertex- and the index - buffer
  this.Device.SetVertexBuffer(this.SkyboxVertices);
  this.Device.Indices = this.SkyboxIndices;

  // choose the appropriate technique for the current render pass
  this.SceneEffect.CurrentTechnique = SceneEffect.Techniques["Skybox"];
  this.SceneEffect.CurrentTechnique.Passes[0].Apply();
  this.SceneEffect.Parameters["WorldViewProjection"].SetValue(WorldViewProjection);

  // finally render the sykbox with disabled depth stencil buffering
  this.Device.DepthStencilState = DepthStencilState.None;
  this.Device.DrawIndexedPrimitives( PrimitiveType.TriangleList, 0, 0, 36, 0, 12);
  this.Device.DepthStencilState = DepthStencilState.Default;


  this.Device.SetRenderTarget(this.GridTexture);
  this.Device.SetRenderTarget(null);
}

什么都没有被渲染 - 我有一个紫色的屏幕！这对你有意义吗！

附：我知道该示例没有多大意义（例如分配和立即取消分配渲染目标）。这里的实际情况要复杂得多，但我能够将问题的本质缩小到这种奇怪的行为，我可以在这个非常简单的示例中进行演示！

【问题讨论】：

标签： xna direct3d

【解决方案1】：

刚刚通过进一步检查API找到了解决方案：将Params.RenderTargetUsage = RenderTargetUsage.PreserveContents添加到PresentationParameter结构中即可解决问题。

在我看来，后台缓冲区的内容 - 就像渲染目标一样 - 在您切换到另一个渲染目标时被销毁。

【讨论】：