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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.