'm using the following code to produce tangents for GL_TRIANGLES, but how do I do it for GL_TRIANGLE_STRIP? Is it possible? It's for a terrain height mesh. I could do it out of triangles but would be inefficient.
for (unsigned int i = 0; i<getNumVertices(); i += 3)
{
// Shortcuts for vertices
glm::vec3 & v0 = getVertice(i + 0);
glm::vec3 & v1 = getVertice(i + 1);
glm::vec3 & v2 = getVertice(i + 2);
// Shortcuts for UVs
glm::vec2 & uv0 = getUV(i + 0);
glm::vec2 & uv1 = getUV(i + 1);
glm::vec2 & uv2 = getUV(i + 2);
// Get normals of the polygon
glm::vec3 &n0 = getNormal(i + 0);
glm::vec3 &n1 = getNormal(i + 1);
glm::vec3 &n2 = getNormal(i + 2);
glm::vec2 deltaUV1 = uv1 - uv0;
glm::vec2 deltaUV2 = uv2 - uv0;
// Edges of the triangle : postion delta
glm::vec3 deltaPos1 = v1 - v0;
glm::vec3 deltaPos2 = v2 - v0;
// Calculate tangent and bitangent
float r = 1.0f / (deltaUV1.x * deltaUV2.y - deltaUV1.y * deltaUV2.x);
glm::vec3 tangent = (deltaPos1 * deltaUV2.y - deltaPos2 * deltaUV1.y) * r;
glm::vec3 bitangent = (deltaPos2 * deltaUV1.x - deltaPos1 * deltaUV2.x) * r;
// Set the same tangent for all three vertices of the triangle.
getTangents()->push_back(glm::normalize(tangent - n0 * glm::dot(n0, tangent)));
getTangents()->push_back(glm::normalize(tangent - n1 * glm::dot(n1, tangent)));
getTangents()->push_back(glm::normalize(tangent - n2 * glm::dot(n2, tangent)));
// Same thing for binormals
getBitangents()->push_back(glm::normalize(bitangent - n0 * glm::dot(n0, bitangent)));
getBitangents()->push_back(glm::normalize(bitangent - n1 * glm::dot(n1, bitangent)));
getBitangents()->push_back(glm::normalize(bitangent - n2 * glm::dot(n2, bitangent)));
}
