为什么使用pixelshader之后alpha无效了？

[corganhejijun]

没有贴图，只指定颜色的三角形都变成了黑色，贴图的透明度无效，求解

shader如下

/// <summary>The brightness offset.</summary>
/// <minValue>-1</minValue>
/// <maxValue>1</maxValue>
/// <defaultValue>0</defaultValue>
float Brightness : register(c1);

/// <summary>The contrast multiplier.</summary>
/// <minValue>0</minValue>
/// <maxValue>2</maxValue>
/// <defaultValue>1.5</defaultValue>
float Contrast : register(c2);

float top : register(c4);
float left : register(c5);
float bottom : register(c6);
float right : register(c7);

struct PS_INPUT
{
    float4 Position   : POSITION;
    float2 Texture    : TEXCOORD;
};

sampler2D Samp : register(S0);

float4 ApplyAdjustments(float4 color)
{
    color.rgb /= color.a;
    
    // Apply contrast.
    color.rgb =((color.rgb - 0.5f) * max(Contrast, 0)) + 0.5f;
    
    // Apply brightness.
    color.rgb += Brightness;
    
    // Return final pixel color.
    color.rgb *= color.a;
    
    return color;
}

//float4 main(float2 uv : TEXCOORD) : COLOR
float4 ps_main( in PS_INPUT In ) : COLOR0
{
	float2 samplePoint;
	samplePoint = In.Texture.xy;
	
	float4 color = tex2D(Samp, samplePoint);
    
    if (samplePoint.y < top)
    {
        return color;
    }
    if (samplePoint.x < left)
    {
        return color;
    }
    if (samplePoint.y > bottom)
    {
        return color;
    }
    if (samplePoint.x > right)
    {
        return color;
    }
    
    color = ApplyAdjustments(color);
    
    return color;
}

[corganhejijun]

搞定，原来是再次绘制的时候shader忘记设为NULL了。
result = m_pd3dDevice->SetPixelShader(NULL);