Unity shader - How to generate normal map based on texture map - unity3d

Question

I'm currently stuck in a shader that i'm writing.
I'm trying to create a rain shader.
I have set up 3 particle system which simulates rain, and a
camera to look at this simulation. The camera view is what I
use as texture. In my shader I am now trying to make a normal map
from that texture map, but I don't know how to do it.
Shader "Unlit/Rain"
{
Properties
{
_MainTex("Albedo (RGB)", 2D) = "white" {}
_Color("Color", Color) = (1,1,1,1)
_NormalIntensity("NormalIntensity",Float) = 1
}
SubShader
{
Tags { "RenderType" = "Opaque" }
LOD 100
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
#include "Lighting.cginc"
#include "AutoLight.cginc"
struct VertexInput {
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
float4 normal : NORMAL;
float3 tangent : TANGENT;
};
struct VertexOutput {
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
float2 uv1 : TEXCOORD1;
float4 normals : NORMAL;
float3 tangentSpaceLight: TANGENT;
};
sampler2D _MainTex;
float4 _MainTex_ST;
half4 _Color;
float _NormalIntensity;
VertexOutput vert(VertexInput v) {
VertexOutput o;
o.normals = v.normal;
o.uv1 = v.uv;
o.vertex = UnityObjectToClipPos( v.vertex );
// o.uv = TRANSFORM_TEX( v.uv, _MainTex ); // used for texture
return o;
}
float4 frag(VertexOutput i) : COLOR{
float4 col2 = tex2D(_MainTex, i.uv1);
return col2 * i.normals * 5;
}
ENDCG
}
}
}
This is what the camera sees. I set the TargetTexture for this camera to be a texture I created.
In my shader I then put that texture as an albedo property
So what I wanna do is now find the normal for that texture to create a bumpmap.

Answer 1

It looks like your "TargetTexture" is giving you back a height map. Here is a post I found about how to turn a height map into a normal map. I've mashed the code you had originally together with the core of that forum post and output the normals as color so you can test and see how this works:
Shader "Unlit/HeightToNormal"
{
Properties
{
_MainTex("Albedo (RGB)", 2D) = "white" {}
_Color("Color", Color) = (1,1,1,1)
_NormalIntensity("NormalIntensity",Float) = 1
_HeightMapSizeX("HeightMapSizeX",Float) = 1024
_HeightMapSizeY("HeightMapSizeY",Float) = 1024
}
SubShader
{
Tags { "RenderType" = "Opaque" }
LOD 100
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
#include "Lighting.cginc"
#include "AutoLight.cginc"
struct VertexInput {
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
float4 normal : NORMAL;
float3 tangent : TANGENT;
};
struct VertexOutput {
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
float2 uv1 : TEXCOORD1;
float4 normals : NORMAL;
//float3 tangentSpaceLight: TANGENT;
};
sampler2D _MainTex;
float4 _MainTex_ST;
half4 _Color;
float _NormalIntensity;
float _HeightMapSizeX;
float _HeightMapSizeY;
VertexOutput vert(VertexInput v) {
VertexOutput o;
o.uv = TRANSFORM_TEX( v.uv, _MainTex ); // used for texture
o.uv1 = v.uv;
o.normals = v.normal;
o.vertex = UnityObjectToClipPos(v.vertex);
return o;
}
float4 frag(VertexOutput i) : COLOR
{
float me = tex2D(_MainTex,i.uv1).x;
float n = tex2D(_MainTex,float2(i.uv1.x, i.uv1.y + 1.0 / _HeightMapSizeY)).x;
float s = tex2D(_MainTex,float2(i.uv1.x, i.uv1.y - 1.0 / _HeightMapSizeY)).x;
float e = tex2D(_MainTex,float2(i.uv1.x + 1.0 / _HeightMapSizeX,i.uv1.y)).x;
float w = tex2D(_MainTex,float2(i.uv1.x - 1.0 / _HeightMapSizeX,i.uv1.y)).x;
// defining starting normal as color has some interesting effects, generally makes this more flexible
float3 norm = _Color;
float3 temp = norm; //a temporary vector that is not parallel to norm
if (norm.x == 1)
temp.y += 0.5;
else
temp.x += 0.5;
//form a basis with norm being one of the axes:
float3 perp1 = normalize(cross(i.normals,temp));
float3 perp2 = normalize(cross(i.normals,perp1));
//use the basis to move the normal i its own space by the offset
float3 normalOffset = -_NormalIntensity * (((n - me) - (s - me)) * perp1 + ((e - me) - (w - me)) * perp2);
norm += normalOffset;
norm = normalize(norm);
// it's also interesting to output temp, perp1, and perp1, or combinations of the float samples.
return float4(norm, 1);
}
ENDCG
}
}
}
To generate a normal map from a height map, you're trying to use the oriented rate of change in your height map to come up with a normal vector which can be represented using 3 float values (or color channels, if it's an image). You can sample the point of image you are on, and then small steps away from that point in four cardinal directions. Using the cross product to guarantee orthogonality you can define a basis. Using your oriented steps on your image, you can scale the two basis vectors and add them together to find a "normal offset", which is the 3D representation approximating the oriented change in value on your heightmap. Basically it's your normal.
You can see the effects of me playing with normal intensity here, and the "normal color" here. When this looks right for your use case, you can try using normals as normals instead of colored output.
Some tweaking of values will probably still be required. Good luck!