Shader works just fine in Unity Editor, but became black in WebGL build - unity3d

Question

I am working on a project which encodes sensor values at different positions into a 3d heatmap of a building. I use a vertex shader for this purpose and this works just fine in Editor:example, but after I built the scene in WebGL, this turned out to be black.
I has tried using constant loop indices or always include this shader in project settings etc., but none of these works. Here are some of the code:
v2f vert(appdata v)
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.worldPos = mul(unity_ObjectToWorld, v.vertex);
o.screenPos = ComputeScreenPos(o.vertex);
UNITY_TRANSFER_FOG(o,o.vertex);
return o;
}
//...
float2 boxIntersection(in float3 ro, in float3 rd, in float3 rad)
{
float3 m = 1.0 / rd;
float3 n = m * ro;
float3 k = abs(m) * rad;
float3 t1 = -n - k;
float3 t2 = -n + k;
float tN = max(max(t1.x, t1.y), t1.z);
float tF = min(min(t2.x, t2.y), t2.z);
if (tN > tF || tF < 0.0) return float2(-1.0, -1.0); // no intersection
return float2(tN, tF);
}
//p in object space
float SampleValue(float3 p) {
float totalValue = 0.0;
float denom = 0.0;
for (int i = 0; i < 34; ++i) { // _DataSize
float4 sd = _SensorData[i];
float dist = length(p - sd.xyz);
totalValue += sd.w / (dist * dist);
denom += 1.0 / (dist * dist);
}
if (denom == 0.0) {
return 0.0;
}
return totalValue / denom;
}
float4 transferFunction(float value) {
float tv = (value - _DataScale.x) / (_DataScale.y - _DataScale.x); // _DataScale.x, _DataScale.y
float4 col = tex2D(_TransferTexture, float2(0.5, tv));
col.w *= _Strength; // _Strength
return float4(col.xyz * col.w, col.w);
}
float4 rayMarch(float3 ro, float3 rd, float dp) {
float3 ro1 = mul(unity_WorldToObject, float4(ro, 1.0));
float3 rd1 = mul(unity_WorldToObject, rd);
float2 t = boxIntersection(ro1, rd1, float3(1, 1, 1) * 0.5);
t.x = length(mul(unity_ObjectToWorld, float4(ro1 + rd1 * max(t.x, 0.0), 1.0)) - ro);
t.y = length(mul(unity_ObjectToWorld, float4(ro1 + rd1 * t.y, 1.0)) - ro);
t.y = min(t.y, dp);
float4 acc = float4(0.0, 0.0, 0.0, 1.0);
float totalDelta = (t.y - t.x);
float delta = totalDelta / float(_RM_Samples - 1.0);
float3 p = ro + t.x * rd;
for (int i = 0; i < 34; ++i) { // _RM_Samples
float v = SampleValue(p);
float4 tf = transferFunction(v);
float tr = exp(-tf.w * delta);
acc.xyz += tf.xyz * acc.w * delta;
acc.w *= tr;
p += delta * rd;
}
return float4(acc.xyz, (1.0 - acc.w) * step(t.x, t.y));
}
fixed4 frag(v2f i) : SV_Target
{
float2 tc = i.screenPos.xy / i.screenPos.w;
float depth = UNITY_SAMPLE_DEPTH(tex2D(_CameraDepthTexture, tc));
float eD = LinearEyeDepth(depth);
float3 ro = _WorldSpaceCameraPos;
float3 rd = normalize(i.worldPos - ro);
float4 col = rayMarch(ro, rd, eD);
//if (col.w < 1) col = float4(1, 0, 0, 1);
//else col = float4(0, 1, 0, 1);
if (wingCullPlaneValue(i.worldPos.xyz) == 0 || cullPlaneValue(i.worldPos.xyz) == 0) {
discard;
}
UNITY_APPLY_FOG(i.fogCoord, col);
return col;
}
Since this works fine in Editor, I don't think there is any error in boxIntersection or rayMarching functions. I wonder if there is anything special in WebGl that it processes the pixels differently, and I has to tweak some codes accordingly. I am new to WebGL and Shader, and would appreciate any help or advice, thanks in advance.

Answer 1

that's because of the step function.
Approximate it with your own sigmoid function (might be expensive)
float emulated_step(float a, float x){
return 1.0/(1+pow(1000, -(x-a)*8192));
}