[LayaAir 2.0]Shader中如何计算每个projCoord对应的screenCoord，归一化为[0,1]

之前网上中的一些实现方法如下：
vec4 computeScreenPos(vec4 projPos)
            {
                vec3 ndc = projPos.xyz / projPos.w;
                vec4 screenPos;
                screenPos.x = (ndc.x * 0.5 + 0.5);
                screenPos.y = u_ProjectionParams.z * (ndc.y * 0.5 + 0.5);
                screenPos.zw = projPos.zw;
                return screenPos;
            }
 
实际应用采样深度纹理的时候，好像是错误的