Question by dtysky · Jun 22, 2019 at 03:33 PM · lighting shaders spotlight

How can I get spot light direction in forward add pass?

Hi everyone, I am writing my own PBR shader that uses physic lights, so it needs range, direction and angle of spot lights. I have get the range and angle by some trick, but has no idea that how to get direction:

 #if defined (SPOT)
     float4 lightCoord = mul(unity_WorldToLight, float4(i.worldPos, 1));
     float range = length(distanceVec) / length(lightCoord.xyz);
     float attenuation = getLightAttenuation(distanceVec, range);
     float cotanHalfSpotAngle = 2. * lightCoord.z / lightCoord.w;
 
     // a trial, but not working
     float3 lightSpaceUnitDir = float3(0., 0., 1.);
     float3 worldLightUnitDir = mul(lightSpaceUnitDir, inverse((float3x3)unity_WorldToLight));
     pbr.L = mul(UNITY_MATRIX_V, worldLightUnitDir);
 
     float outerCutoff = atan(1. / cotanHalfSpotAngle);
     float cutoff = max(outerCutoff - .05, 0.);
     float theta = dot(normalize(distanceVec), pbr.L);
     float epsilon = cos(outerCutoff) - cos(cutoff);
     float intensity = clamp((theta - cos(cutoff)) / epsilon, 0.0, 1.0);
     attenuation *= intensity;
 #endif

How can I get it? Why does not unity give us this information when we need to calculate attenuation ourselves?

Thanks!