我的后处理着色器在XNA中的偏移怎么样？

Question

我正在XNA 4.0中实现一个后处理着色器。我意识到原始图片（场景渲染器的输出）移动了一小段距离。当我尝试实现MotionBlur效果时，它变得非常明显。看图像。场景渲染器的输出在中心是一个清晰的黄色十字。应用MotionBlur后，图像变得模糊（我没有在场景中移动任何东西，因此黄色十字应该像原始十字一样清晰）。我很困惑。谁能帮我？感谢。

（好吧，我到目前为止无法上传图片......）

以下是MotionBlur计划的代码片段：

protected void CreateQuad() {
        m_vertex = new VertexPositionTexture[4];
        m_vertex[0] = new VertexPositionTexture(
            new Vector3(1, 1, 1), new Vector2(1, 0));
        m_vertex[1] = new VertexPositionTexture(
            new Vector3(1, -1, 1), new Vector2(1, 1));
        m_vertex[2] = new VertexPositionTexture(
            new Vector3(-1, 1, 1), new Vector2(0, 0));
        m_vertex[3] = new VertexPositionTexture(
            new Vector3(-1, -1, 1), new Vector2(0, 1));
        m_vertexBuffer = new VertexBuffer(
            m_game.GraphicsDevice, 
            typeof(VertexPositionTexture), 
            4, 
            BufferUsage.None);
        m_vertexBuffer.SetData<VertexPositionTexture>(m_vertex);
    }
    protected void CreateRenderTarget() {
        m_color = new RenderTarget2D(m_game.GraphicsDevice,
            m_game.GraphicsDevice.PresentationParameters.BackBufferWidth,
            m_game.GraphicsDevice.PresentationParameters.BackBufferHeight);
        m_accColorRead = new RenderTarget2D(
            m_game.GraphicsDevice,
            m_game.GraphicsDevice.PresentationParameters.BackBufferWidth,
            m_game.GraphicsDevice.PresentationParameters.BackBufferHeight);
        ClearRenderTargetContent(m_accColorRead);
        m_accColorWrite = new RenderTarget2D(
            m_game.GraphicsDevice,
            m_game.GraphicsDevice.PresentationParameters.BackBufferWidth,
            m_game.GraphicsDevice.PresentationParameters.BackBufferHeight);
    }
    public void DoRender(GameTime _gameTime, DebugScene _debugScene) {
        m_game.GraphicsDevice.SetRenderTarget(m_color);
        m_game.GraphicsDevice.Clear(Color.Blue);
        _debugScene.DoRender(_gameTime);
        m_game.GraphicsDevice.SetRenderTarget(null);
        m_effect.CurrentTechnique = m_effect.Techniques["Main"];
        // write to acc
        m_game.GraphicsDevice.SetRenderTarget(m_accColorWrite);
        m_effect.Parameters["ColorMap"].SetValue((Texture2D)m_color);
        m_effect.Parameters["AccColorMap"].SetValue((Texture2D)m_accColorRead);
        m_effect.Parameters["gBlurIntensity"].SetValue(0.9f);
        m_effect.CurrentTechnique.Passes["Blur"].Apply();
        m_game.GraphicsDevice.Clear(Color.Black);
        DrawQuad();
        m_game.GraphicsDevice.SetRenderTarget(null);
        // output
        m_game.GraphicsDevice.Clear(Color.Black);
        m_effect.Parameters["ColorMap"].SetValue((Texture2D)m_accColorWrite);
        m_effect.CurrentTechnique.Passes["Final"].Apply();
        DrawQuad();
        // swap
        RenderTarget2D tmp = m_accColorRead;
        m_accColorRead = m_accColorWrite;
        m_accColorWrite = tmp;
    }

以下是MotionBlur着色器的代码：

texture ColorMap;
sampler ColorMapSampler = sampler_state
{
   Texture = <ColorMap>;
   MinFilter = Linear;
   MagFilter = Linear;
   MipFilter = Linear; 
   AddressU = Clamp;
   AddressV = Clamp;
};

texture AccColorMap;
sampler AccColorMapSampler = sampler_state
{
   Texture = <AccColorMap>;
   MinFilter = Linear;
   MagFilter = Linear;
   MipFilter = Linear;
   AddressU = Clamp;
   AddressV = Clamp;
};

float gBlurIntensity;
struct VS_OUT
{
    float4 Pos : POSITION;
    float2 Tex : TEXCOORD0;
};

VS_OUT VS(float4 pos : POSITION, float2 tex : TEXCOORD0)
{
    VS_OUT Out = (VS_OUT)0;
    Out.Pos = pos;     
    return Out;
}

float4 PS(VS_OUT IN) : COLOR
{
    float4 color = tex2D(ColorMapSampler, IN.Tex);
    float4 accColor = tex2D(AccColorMapSampler, IN.Tex);
    return lerp(color, accColor, gBlurIntensity);
}

float4 PS_Final(VS_OUT IN) : COLOR
{
    return tex2D(ColorMapSampler, IN.Tex);
}
technique Main
{
pass Blur
{
        VertexShader = compile vs_2_0 VS();
        ZEnable = false;
        ZWriteEnable = false;
        AlphaBlendEnable = false;
        CullMode = None;
        PixelShader = compile ps_2_0 PS();
}
    pass Final
    {
        VertexShader = compile vs_2_0 VS();
        ZEnable = false;
        ZWriteEnable = false;
        AlphaBlendEnable = false;
        CullMode = None;
        PixelShader = compile ps_2_0 PS_Final();
    }
}