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creating normals from alpha/heightmap inside a shader

http://www.polycount.com/forum/showthread.php?t=117185

 

I am making some custom terrain shaders with strumpy‘s editor and I want to be able to create normals based on my blend mask. Does anyone know how I can turn grayscale data into basic normal mapping info? I have seen someone do this in unreal but I can‘t remember where.

 

You probably want to get the difference of the values pixel-by-pixel using ddx, I think.

Off the top of my head... for CG/HLSL;

float heightmap = your height map value;
float3 normal;
normal.x = ddx(heightmap);
normal.y = ddy(heightmap);
normal.z = sqrt(1 - normal.x*normal.x - normal.y * normal.y); // Reconstruct z component to get a unit normal.

For OpenGL, I think the functions are dFdx and dFdy.

DirectX11 has ddx_fine and ddy_fine which I think give more accurate results.


That‘ll give you the normal in, ehr... screen space I think?

Otherwise you can sample the heightmap multiple times, offsetting it by a pixel and working out the difference from those values. That should get you it in whatever space the base normal is in.

Nicked frm here; http://www.gamedev.net/topic/594781-...mal-algorithm/

float me = tex2D(heightMapSampler,IN.tex).x;float n = tex2D(heightMapSampler,float2(IN.tex.x,IN.tex.y+1.0/heightMapSizeY)).x;float s = tex2D(heightMapSampler,float2(IN.tex.x,IN.tex.y-1.0/heightMapSizeY)).x;float e = tex2D(heightMapSampler,float2(IN.tex.x+1.0/heightMapSizeX,IN.tex.y)).x;float w = tex2D(heightMapSampler,float2(IN.tex.x-1.0/heightMapSizeX,IN.tex.y)).x;                //find perpendicular vector to norm:        float3 temp = norm; //a temporary vector that is not parallel to normif(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(norm,temp));float3 perp2 = normalize(cross(norm,perp1));//use the basis to move the normal in its own space by the offset        float3 normalOffset = -bumpHeightScale*(((n-me)-(s-me))*perp1 + ((e-me)-(w-me))*perp2);norm += normalOffset;norm = normalize(norm);

 

Gave it a try out of curiosity.

Here‘s the multi-sample method in a stripped-down surface shader.

I had to change the handedness from the code above to match Unity (changing the sign of the operation when sampling the e and w values from + to - and vice versa).

 

Shader "Debug/Normal Map From Height" {    Properties {        _Color ("Main Color", Color) = (1,1,1,1)        _MainTex ("Diffuse (RGB) Alpha (A)", 2D) = "white" {}        _BumpMap ("Normal (Normal)", 2D) = "bump" {}        _HeightMap ("Heightmap (R)", 2D) = "grey" {}        _HeightmapStrength ("Heightmap Strength", Float) = 1.0        _HeightmapDimX ("Heightmap Width", Float) = 2048        _HeightmapDimY ("Heightmap Height", Float) = 2048    }    SubShader{        Tags { "RenderType" = "Opaque" }        CGPROGRAM            #pragma surface surf NormalsHeight            #pragma target 3.0            struct Input            {                float2 uv_MainTex;            };            sampler2D _MainTex, _BumpMap, _HeightMap;            float _HeightmapStrength, _HeightmapDimX, _HeightmapDimY;            void surf (Input IN, inout SurfaceOutput o)            {                o.Albedo = fixed3(0.5);                float3 normal = UnpackNormal(tex2D(_BumpMap, IN.uv_MainTex));                float me = tex2D(_HeightMap,IN.uv_MainTex).x;                float n = tex2D(_HeightMap,float2(IN.uv_MainTex.x,IN.uv_MainTex.y+1.0/_HeightmapDimY)).x;                float s = tex2D(_HeightMap,float2(IN.uv_MainTex.x,IN.uv_MainTex.y-1.0/_HeightmapDimY)).x;                float e = tex2D(_HeightMap,float2(IN.uv_MainTex.x-1.0/_HeightmapDimX,IN.uv_MainTex.y)).x;                float w = tex2D(_HeightMap,float2(IN.uv_MainTex.x+1.0/_HeightmapDimX,IN.uv_MainTex.y)).x;                float3 norm = normal;                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(norm,temp));                float3 perp2 = normalize(cross(norm,perp1));                //use the basis to move the normal in its own space by the offset                float3 normalOffset = -_HeightmapStrength * ( ( (n-me) - (s-me) ) * perp1 + ( ( e - me ) - ( w - me ) ) * perp2 );                norm += normalOffset;                norm = normalize(norm);                o.Normal = norm;            }            inline fixed4 LightingNormalsHeight (SurfaceOutput s, fixed3 lightDir, fixed3 viewDir, fixed atten)            {                viewDir = normalize(viewDir);                lightDir = normalize(lightDir);                s.Normal = normalize(s.Normal);                float NdotL = dot(s.Normal, lightDir);                _LightColor0.rgb = _LightColor0.rgb;                fixed4 c;                c.rgb = float3(0.5) * saturate ( NdotL ) * _LightColor0.rgb * atten;                c.a = 1.0;                return c;            }        ENDCG    }    FallBack "VertexLit"}

 

Derivative method works, but it‘s fucking ugly ‘cause it‘s in screen space - really noisy.

ddx_fine might give better results in DX11, but it looks like crap in DX9.