Lol, when I saw the number of commit I was thinking "wow, is this using the old history again", but no, it's just your regular crazy PR touching 73 files :p

My only comment regarding the new tutorial so far is: can we do the without the custom shader? Maybe by loading a texture onto the mesh? We could add a function texture_from_colormap to the opengl/ folder (if we don't have one already). Could be like this:

void texture_from_colormap(const Eigen::MatrixXd &rgb, GLuint & id)
{
  int width = 1;
  int height = (int) rgb.rows();

  Eigen::Matrix<unsigned char, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor> cmap;
  if (rgb.maxCoeff() > 1.0) {
    cmap = rgb.cast<unsigned char>();
  } else {
    cmap = (rgb.array() * 255.f).cast<unsigned char>();
  }
  assert(cmap.cols() == 3);
  cmap.conservativeResize(cmap.rows(), 4);
  cmap.col(3).setConstant(255);

  if (id == 0) {
    glGenTextures(1, &id);
  }
  glBindTexture(GL_TEXTURE_2D, id);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexImage2D(
    GL_TEXTURE_2D, 0, GL_RGBA,
    width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, cmap.data());
  glGenerateMipmap(GL_TEXTURE_2D);
  glBindTexture(GL_TEXTURE_2D, 0);
}

I like this idea. We should do it as a separate PR and change all of the tutorials that use scalar field visualization. We should also try to expose it nicely in the viewer with something like set_per_vertex_data.

Which tutorials require scalar field visualization? I don't think there are that many. We could name the function ViewerData::set_scalars to be coherent with set_normals/set_colors/set_uv. It would simply set the v texture coordinate per vertex, with a u=0? I mean we could also reuse set_uv if the matrix has only 1 column.

There are two questions to answer I think:

• What about normalization? I think it should be left to the user to normalize the scalar field, and values are simply clamped to the range [0, 1].
• We can also add support for periodic colormap. Twilight is a perceptually uniform colormap introduced in the latest version of matplotlib. Could be useful too :p

From the tutorial there are quite a few:

• 202_GaussianCurvature
• 203_CurvatureDirections
• 204_Gradient
• 206_GeodesicDistance
• 302_Sort
• 303_LaplaceEquation
• 304_LinearEqualityConstraints
• 305_QuadraticProgramming
• 306_EigenDecomposition
• 403_BoundedBiharmonicWeights
• 702_WindingNumber
• 704_SignedDistance
• 712_DataSmoothing
• 716_HeatGeodesics

I agree about the normalization, though it's easy enough to provide parameters and overloads to control that.

Periodic colormap makes sense to add, too.

Yeah doesn't hurt to have an optional bool normalize argument. I'll put that on my libigl todo list.