I am drawing a mesh of triangles using glDrawElements and would like to be able to pick/select a triangle using the mouse click. The mesh of triangles can be very big.
In fixed-function OpenGL there is the possibility of using GL_SELECT: http://content.gpwiki.org/index.php/OpenGL:Tutorials:Picking .. However I am only interested in using OpenGL core profile.
Another possibility would be to use 'color coding':
http://www.lighthouse3d.com/opengl/picking/index.php?color1
http://www.opengl.org/resources/faq/technical/selection.htm
.. but as far as I know its not possible to indicate per triangle information yet when using glDrawElements?
Finally I could do CPU based picking by shooting a pick ray through the mouse location, but this would be quite slow since I guess I would have to transform the triangles on the CPU, so I would prefer a GPU based solution.
Does anyone have a suggestion on what is the best way do picking when using glDrawElements in OpenGL core profile?
About the 'color coding' approach, you could use gl_PrimitiveID to fill the color coded buffer(s) using a proper fragment shader, this would basically give you the index of the drawn triangle.
About the CPU based picking, you could use an existing library that handles the acceleration structures, and ray-mesh intersection, such as Bullet or Opcode.
The 'best' option for you depends of your use case, hard to tell.