Recognize specific materials in Unity shader? (E.g. for heat vision) - unity3d

Question

If I have a Unity shader which is acting as a basic screenwide image filter, would there be any way (outside of making a material glowing/ unshaded) to "recognize" specific pixels of a material? Let's say I want a heat vision filter, and allow specific objects to be considered "hot". How could the pixel color shader check their color or anything else and understand "this is hot"? (If I made it glowing/ unshaded, I could encode specific properties into subtle rgb changes, e.g. maybe if all of rgb end in *.***5 it would mean hot, but that wouldn't work with shading applied.) Thanks!

Answer 1

First you should convert your Image to grayscale then apply a color spectrum to It.If you look at below Image,
the closer to the white Is warmer and the closer to black Is colder.
then you can add this effect by using Replacement Shader.
Shader"Hidden/HeatMap"{
Properties{
_MainTex("_MainTex", 2D) = "white"{}
_Amount("Amount",Float) = 1
[Toggle]_Enable("Enable",Float) = 1
}
SubShader{
Pass{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma fragmentoption ARB_precision_hint_fastest
#include "UnityCG.cginc"
struct appdata{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
};
sampler2D _MainTex;
float _Amount,_Enable;
struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
};
v2f vert(appdata v)
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.uv = v.uv;
return o;
}
fixed greyScale(fixed3 rgb) {
return dot(rgb, fixed3(0.29, 0.60, 0.11));
}
fixed3 heatMap(fixed greyValue) {
fixed3 heat = fixed3(0,0,0);
heat.r = smoothstep(0.4, 0.8, greyValue);
half OutColorGreen = smoothstep(0.0, 0.7, greyValue);
half InColorGreen = smoothstep(1.0, 0.7, greyValue);
heat.g = min(InColorGreen,OutColorGreen);
float OutColorBlue = smoothstep(1.0, 0.0, greyValue);
float InColorBlue = smoothstep(0.0, 0.25, greyValue);
heat.b = min(OutColorBlue,InColorBlue);
return heat;
}
fixed4 frag(v2f i) : COLOR{
fixed2 uv = i.uv;
fixed3 mainTex = tex2D(_MainTex, uv).rgb;
fixed grayValueA = greyScale(mainTex);
fixed3 rgbOut;
rgbOut = heatMap(uv.y);
rgbOut = heatMap(grayValueA * _Amount);
return fixed4(lerp(mainTex,rgbOut,_Enable),1);
}ENDCG
}
}
}
Let's check it out once more:
First you should convert your Image to grayscale.
then try to recolorize It by a method:
Using ZBuffer
In computer graphics, z-buffering, also known as depth buffering, is the management of image depth coordinates in 3D graphics, usually done in hardware, sometimes in software.
https://en.wikipedia.org/wiki/Z-buffering
using UnityEngine;
[ExecuteInEditMode]
public class CameraScript : MonoBehaviour {
public Material mat;
void Start()
{
GetComponent<Camera>().depthTextureMode = DepthTextureMode.Depth;
}
void OnRenderImage(RenderTexture source, RenderTexture destination)
{
Graphics.Blit(source, destination, mat);
}
}
Shader "Custom/HeatVision"
{
SubShader
{
Tags { "RenderType"="Opaque" }
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
struct v2f
{
float4 pos : SV_POSITION;
float4 screenuv : TEXCOORD1;
};
v2f vert (appdata_base v)
{
v2f o;
o.pos = UnityObjectToClipPos(v.vertex);
o.screenuv = ComputeScreenPos(o.pos);
return o;
}
sampler2D _CameraDepthTexture;
fixed greyScale(fixed3 rgb) {
return dot(rgb, fixed3(0.29, 0.60, 0.11));
}
fixed3 heatMap(fixed greyValue) {
fixed3 heat = fixed3(0,0,0);
heat.r = smoothstep(0.4, 0.8, greyValue);
half OutColorGreen = smoothstep(0.0, 0.7, greyValue);
half InColorGreen = smoothstep(1.0, 0.7, greyValue);
heat.g = min(InColorGreen,OutColorGreen);
float OutColorBlue = smoothstep(1.0, 0.0, greyValue);
float InColorBlue = smoothstep(0.0, 0.25, greyValue);
heat.b = min(OutColorBlue,InColorBlue);
return heat;
}
fixed4 frag (v2f i) : SV_Target
{
float2 uv = i.screenuv.xy / i.screenuv.w;
fixed3 mainTex = tex2D(_CameraDepthTexture, uv).rgb;
fixed grayValueA = greyScale(mainTex);
fixed3 rgbOut;
float Intensity = 15;
float depth = SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, uv)*Intensity;
rgbOut = heatMap(uv.y);
rgbOut = heatMap(depth);
return float4(rgbOut.rgb,1);
}
ENDCG
}
}
}