中级Shader教程24 水专题01:两种雨实现方式

float2 ruv = uv / float2(_ScreenParams.x/_ScreenParams.y,1.0);//原始uv
//宽高比正常uv
uv = (ruv * 2.0 - 1.0) *  float2(_ScreenParams.x/_ScreenParams.y,1.0);
float2 st =  uv * float2(.5+(ruv.y+1.0)*0.5, .03)+float2(ftime*.2-ruv.y*.1, ftime*.2);
//拉伸实现
float f = tex2D(_NoiseTex, st).y * tex2D(_NoiseTex, st*.773).x * 1.55;
f = clamp(pow(abs(f), 23.0) * 13.0, 0.0, (ruv.y-.2)*.14);
col += float3(f,f,f); 

float3 hitPos = RayCastScene();
float dis = 1.;
 for (int i = 0; i < LayerNum; i++)
{
    float3 plane = vCameraPos + originalRayDir * dis;
    //判定是否被雨阻挡
    if (plane.z < hitPos.z)
    {
        //根据z值缩小雨滴  透视模拟
        float f = pow(dis, .45)+.25;
        float2 st =  f * (uv * float2(1.5, .05)+float2(-ftime*.1+uv.y*.5, ftime*.12));
        // 拉伸uv后采集NoiseTex
        f = (tex2D(_NoiseTex, st * .5, -99.0).x + tex2D(_NoiseTex, st*.284, -99.0).y);
        // 让雨在离地面的地方变得透明
        f = clamp(pow(abs(f)*.5, 29.0) * 140.0, 0.00, uv.y*.4+.05);
        float3 bri = float3(.25);
        //光照处理
        for (int t = 0; t < NUM_LIGHTS; t++){
            float3 v3 = lightArray[t].xyz - plane.xyz;
            float l = dot(v3, v3);
            l = max(3.0-(l*l * .02), 0.0);
            bri += l * lightColours[t];
        }
        col += bri*f;
    }
    dis += 3.5;
}
col = clamp(col, 0.0, 1.0);