[SOLVED!] Darken Shadows over distance - Deferred Shading question

Hi everyone,

I am trying to adjust shadow strength over distance. This is because I want cave entrances and shadows in general to be full strength when they are far away -and I can hide all interior geometry inside such caves until the player comes close enough for shadow strength to be greater than 0,0,0 black. For this particular project it would give a very big performance boost without resorting to dithered LOD fading or other unity techniques (which I have given a fair bit of testing already).

I have already identified the right part of the Internal-ScreenSpaceShadows code that needs to be changed.

The problem is finding the distance from the camera to the target pixel. I want to avoid reading the camera depth texture again, but I can't seem to make it work.

     float someDistanceNumber = 100;
     float shadowDarken = smoothstep( 0, someDistanceNumber, distance( vpos, i.pos ));

These lines of code (specifically the shadowDarken float) right at the end of the shader seems to be returning either 1 or 0 no matter what I do. What am I doing wrong here?

The full frag shader from Internal-ScreenSpaceShadows is pasted here for convenience (just the pcf5x5 is relevant to me):

 fixed4 frag_pcf5x5(v2f i) : SV_Target
 {
     UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i); // required for sampling the correct slice of the shadow map render texture array
 
     float3 vpos = computeCameraSpacePosFromDepth(i);
 
     // sample the cascade the pixel belongs to
     float4 wpos = mul(unity_CameraToWorld, float4(vpos,1));
     fixed4 cascadeWeights = GET_CASCADE_WEIGHTS(wpos, vpos.z);
     float4 coord = GET_SHADOW_COORDINATES(wpos, cascadeWeights);
 
     float2 receiverPlaneDepthBiasCascade0 = 0.0;
     float2 receiverPlaneDepthBias = 0.0;
 #if UNITY_USE_RECEIVER_PLANE_BIAS
     // Reveiver plane depth bias: need to calculate it based on shadow coordinate
     // as it would be in first cascade; otherwise derivatives
     // at cascade boundaries will be all wrong. So compute
     // it from cascade 0 UV, and scale based on which cascade we're in.
     // 
     float3 coordCascade0 = getShadowCoord_SingleCascade(wpos);
     receiverPlaneDepthBiasCascade0 = getReceiverPlaneDepthBias(coordCascade0.xyz);
     float biasMultiply = dot(cascadeWeights,unity_ShadowCascadeScales);
 
     receiverPlaneDepthBias = receiverPlaneDepthBiasCascade0 * biasMultiply;
 
     // Static depth biasing to make up for incorrect fractional
     // sampling on the shadow map grid; from "A Sampling of Shadow Techniques"
     // (http://mynameismjp.wordpress.com/2013/09/10/shadow-maps/)
     float fractionalSamplingError = 2 * dot(_ShadowMapTexture_TexelSize.xy, abs(receiverPlaneDepthBias));
     coord.z -= min(fractionalSamplingError, UNITY_RECEIVER_PLANE_MIN_FRACTIONAL_ERROR);
 #endif
 
 
     half shadow = sampleShadowmap_PCF5x5(coord, receiverPlaneDepthBias);
 
 
     // Blend between shadow cascades if enabled
     //
     // Not working yet with split spheres, and no need when 1 cascade
 #if UNITY_USE_CASCADE_BLENDING && !defined(SHADOWS_SPLIT_SPHERES) && !defined(SHADOWS_SINGLE_CASCADE)
     half4 z4 = (float4(vpos.z,vpos.z,vpos.z,vpos.z) - _LightSplitsNear) / (_LightSplitsFar - _LightSplitsNear);
     half alpha = dot(z4 * cascadeWeights, half4(1,1,1,1));
 
     UNITY_BRANCH
         if (alpha > 1 - UNITY_CASCADE_BLEND_DISTANCE)
         {
             // get alpha to 0..1 range over the blend distance
             alpha = (alpha - (1 - UNITY_CASCADE_BLEND_DISTANCE)) / UNITY_CASCADE_BLEND_DISTANCE;
 
             // sample next cascade
             cascadeWeights = fixed4(0, cascadeWeights.xyz);
             coord = GET_SHADOW_COORDINATES(wpos, cascadeWeights);
 
 #if UNITY_USE_RECEIVER_PLANE_BIAS
             biasMultiply = dot(cascadeWeights,unity_ShadowCascadeScales);
             receiverPlaneDepthBias = receiverPlaneDepthBiasCascade0 * biasMultiply;
             fractionalSamplingError = 2 * dot(_ShadowMapTexture_TexelSize.xy, abs(receiverPlaneDepthBias));
             coord.z -= min(fractionalSamplingError, UNITY_RECEIVER_PLANE_MIN_FRACTIONAL_ERROR);
 #endif
 
             half shadowNextCascade = sampleShadowmap_PCF3x3(coord, receiverPlaneDepthBias);
 
             shadow = lerp(shadow, shadowNextCascade, alpha);
         }
 #endif

     float someDistanceNumber = 100;
     float shadowDarken = smoothstep( 0, someDistanceNumber, distance( vpos, i.pos ));
     shadow = lerp(shadow, 0.5 + 0.5 * shadow, shadowDarken);
 
     return shadow;
 }

It may be of interest that passing the fade/distance as a TEXCOORD from the vertex shader also seems to not be working, and I'm not sure why this is happening either.