Update

resources/terrain/README.md

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+Textures are CC0 from https://cc0textures.com/ adapted for Ogre

resources/terrain/TerrainSurface.glsl

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+void transformToTS(in vec3 TSnormal, in mat3 normalMatrix, inout vec3 normal)
+{
+    // derive the tangent space basis
+    // we do this in the pixel shader because we don't have per-vertex normals
+    // because of the LOD, we use a normal map
+    // tangent is always +x or -z in object space depending on alignment
+#ifdef TERRAIN_ALIGN_Y_Z
+    vec3 tangent = vec3(0, 0, -1);
+#else
+    vec3 tangent = vec3(1, 0, 0);
+#endif
+    normal = normalize(normal);
+    tangent = normalize(mul(normalMatrix, tangent));
+    vec3 binormal = cross(tangent, normal);
+    // note, now we need to re-cross to derive tangent again because it wasn't orthonormal
+    tangent = cross(normal, binormal);
+    // derive final matrix
+    mat3 TBN = mtxFromCols(tangent, binormal, normal);
+
+    normal = mul(TBN, TSnormal);
+}
+
+void getShadowFactor(in sampler2D lightmap, in vec2 uv, inout float shadowFactor)
+{
+    float lmShadow = texture2D(lightmap, uv).x;
+    shadowFactor = min(shadowFactor, lmShadow);
+}
+
+#define MIN_BLEND_WEIGHT 0.0039 // 1/255
+
+void blendTerrainLayer(in float blendWeight, in f32vec2 uv0, in float uvMul,
+#ifdef TERRAIN_PARALLAX_MAPPING
+                    in vec3 viewPos, in float scaleBias, in mat3 TBN,
+#endif
+#ifdef TERRAIN_NORMAL_MAPPING
+                    in sampler2D normtex, inout vec3 normal,
+#endif
+                    in sampler2D difftex, inout vec4 diffuseSpec)
+{
+    if(blendWeight < MIN_BLEND_WEIGHT)
+        return;
+
+    // generate UV
+    vec2 uv = mod(uv0 * uvMul, 1.0);
+
+#ifdef TERRAIN_PARALLAX_MAPPING
+    SGX_Generate_Parallax_Texcoord(normtex, uv, viewPos, scaleBias, TBN, uv);
+#endif
+
+    // sample diffuse texture
+    vec4 diffuseSpecTex = texture2D(difftex, uv);
+    // apply to common
+    diffuseSpec = mix(diffuseSpec, diffuseSpecTex, blendWeight);
+
+#ifdef TERRAIN_NORMAL_MAPPING
+    vec3 TSnormal;
+    // access TS normal map
+    SGX_FetchNormal(normtex, uv, TSnormal);
+    // Partial Derivative Blending https://blog.selfshadow.com/publications/blending-in-detail/
+    normal = normalize(vec3(mix(normal.xy*TSnormal.z, TSnormal.xy*normal.z, blendWeight), TSnormal.z*normal.z));
+#endif
+}
+
+//-----------------------------------------------------------------------------
+void SGX_CalculateTerrainTBN(in vec3 normal, in mat3 normalMatrix, out mat3 TBN)
+{
+    // derive the tangent space basis
+    // we do this in the pixel shader because we don't have per-vertex normals
+    // because of the LOD, we use a normal map
+    // tangent is always +x or -z in object space depending on alignment
+	#ifdef TERRAIN_ALIGN_Y_Z
+		vec3 tangent = vec3(0, 0, -1);
+	#else
+		vec3 tangent = vec3(1, 0, 0);
+	#endif
+    normal = normalize(normal);
+    tangent = normalize(mul(normalMatrix, tangent));
+    vec3 binormal = cross(tangent, normal);
+    // note, now we need to re-cross to derive tangent again because it wasn't orthonormal
+    tangent = cross(normal, binormal);
+    // derive final matrix
+    TBN = mtxFromCols(tangent, binormal, normal);
+}

resources/terrain/TerrainTransforms.glsl

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+/**
+ * @param delta: lodDelta, lodThreshold (vertex attribute)
+ * @param lodMorph: morph amount, morph targetLOD (uniform)
+ */
+void applyLODMorph(vec2 delta, vec2 lodMorph, inout float height
+#ifdef TERRAIN_DEBUG
+, out vec2 lodInfo
+#endif
+)
+{
+    // determine whether to apply the LOD morph to this vertex
+    // we store the deltas against all vertices so we only want to apply
+    // the morph to the ones which would disappear.
+    // If we subtract
+    // the lodThreshold from the targetLOD, and arrange to only morph if the
+    // result is negative (it will only be -1 in fact, since after that
+    // the vertex will never be indexed), we will achieve our aim.
+    // sign(lodThreshold - targetLOD) == -1 is to morph
+
+    // this will either be 1 (morph) or 0 (don't morph)
+    float toMorph = -min(0.0, sign(delta.y - lodMorph.y));
+    height += delta.x * toMorph * lodMorph.x;
+
+#ifdef TERRAIN_DEBUG
+    // LOD level (-1 since value is target level, we want to display actual)
+    lodInfo.x = (lodMorph.y - 1) / NUM_LODS;
+    // LOD morph
+    lodInfo.y = toMorph * lodMorph.x;
+#endif
+}
+
+void expandVertex(mat4 idxToObjectSpace, float baseUVScale, vec2 idx, float height, out vec4 position, out vec2 uv)
+{
+    position = mul(idxToObjectSpace, vec4(idx, height, 1));
+    uv = vec2(idx.x * baseUVScale, 1.0 - idx.y * baseUVScale);
+}