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 norm
if(norm.x==)
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) = (,,,)
_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) =
_HeightmapDimY ("Heightmap Height", Float) =
} 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==)
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.
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