43 lines
1.3 KiB
Text
43 lines
1.3 KiB
Text
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#version 330 core
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uniform sampler2D normal_tex;
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uniform int normalmap_dds = 0;
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/*
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* Create a cotangent frame without a pre-computed tangent basis.
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* "Normal Mapping Without Precomputed Tangents" by Christian Schüler (2013).
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* http://www.thetenthplanet.de/archives/1180
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*/
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mat3 cotangent_frame(vec3 N, vec3 p, vec2 uv)
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{
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// get edge vectors of the pixel triangle
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vec3 dp1 = dFdx(p);
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vec3 dp2 = dFdy(p);
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vec2 duv1 = dFdx(uv);
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vec2 duv2 = dFdy(uv);
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// solve the linear system
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vec3 dp2perp = cross(dp2, N);
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vec3 dp1perp = cross(N, dp1);
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vec3 T = dp2perp * duv1.x + dp1perp * duv2.x;
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vec3 B = dp2perp * duv1.y + dp1perp * duv2.y;
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// construct a scale-invariant frame
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float invmax = inversesqrt(max(dot(T,T), dot(B,B)));
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return mat3(T * invmax, B * invmax, N);
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}
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/*
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* Perturb the interpolated vertex normal N according to a normal map.
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* V is the view vector (eye to vertex, not normalized). Both N and V must be
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* in the same space.
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*/
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vec3 perturb_normal(vec3 N, vec3 V, vec2 texcoord)
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{
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vec3 normal = texture(normal_tex, texcoord).rgb * 2.0 - 1.0;
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if (normalmap_dds > 0) {
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// DDS has flipped normals
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normal = -normal;
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}
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mat3 TBN = cotangent_frame(N, V, texcoord);
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return normalize(TBN * normal);
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}
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