I’m using OpenGL (Version 4.4) (and C++ if that matters).

I’ve created a terrain renderer, the terrain is stored as a 3D scalar field (isosurface/voxels). It uses a slightly modified version of Marching Cubes, to perform polygonization (converting the scalar field to triangles).

Currently I’m texturing the terrain using a horizontal (grass) texture and a vertical (dirt) texture. Then when applying the texture I simply calculate the amount of the horizontal and vertical texture that is required on the current triangle, depending on the normals of the current triangle. Thereby the more a normal is pointing upwards (or downward) the more dominant the horizontal (grass) texture will be.

Terrain Renderer in Action

Fullscreen Image

Now the question is, what would be the best (or a good) way to perform Multi-Texturing on the terrain? I will give all the values in the scalar field a voxel type value as well. So the main question is how should the rendering be handled. I have a couple of ideas of how this could be done, but I’m not sure which of my ideas would be the best one to do or if there’s even a better way.

First Idea

• Bind all the needed textures, thereby call glActiveTexture(...) for each texture there is.
• Now the mesh can be rendered using a single glDraw*(...) call.
• This of course only works if the Shader knows when and where to use each texture, or
  that the info for using each texture, is stored within the buffer, as some sort of
  value which the Shader uses, to “detect” which texture should be used. As mentioned previously this could be the voxel type value.

Problem: The maximum amount of textures which can be bound simultaneously is very limited, so that could (and probably would) create some problems.

Second Idea

• Bind a single texture and call glDraw*(...) with a specific first and count value, so that only a part of the mesh is rendered. Which of course is the part which uses the bound texture.
• Thereby loop the above until the whole mesh is rendered using all the individual textures.

I don’t see any real problem with this idea, the only extra thing we need to take in mind, is that all the triangles need to be sorted according to their voxel type value.

Though we wouldn’t be able to fade the textures, like in the image above.

Third Idea

• Split the mesh into individual buffers (VBOs and VAOs), so that each buffer only uses a single (or a couple) texture(s). Basically the same as the Second Idea though here the buffer would physically be split according to the textures.

Fourth Idea?

or is there an even better way?

Side Note

• Each texture has it’s own handle, thereby none of them can be used as a Texture Atlas.